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Sump/sewage pump size for run-off ground water discharge questions.

Sump/sewage pump size for run-off ground water discharge questions.

Sump/sewage pump size for run-off ground water discharge questions.

(OP)
Newly found this forum and want to seek some insights on this water problem I've been trying to solve for our recently bought old house (built in 50s).

House we bought a year ago had this strange setup. In order to accommodate the addition of a 2-car garage and the sunroom above at the rear of original house, they extended/carved the driveway into the original backyard, and now the driveway is downward, with the end of it enclosed by the retaining walls. The only route that the run off water from the driveway, and from neighboring lot, backyard is a grated channel with a 4 inch PVC pipe buried under garage floor connected to a sump pit at the corner of the garage. Currently I have a liberty LE50 sewage pump in the pit, which goes 8400 gph at 5ft, but the discharge tube that connects to it is half inch smaller than the pump's 2 inch port. That tubing is partially buried into the cinder block wall then goes underneath/around the house to the street side drain. Pump is hooked up to the backup generator, so the power failure was not too much of a concern. Here is the problem:

The inlet 4inch PVC is at a rather low height of the pit, along with some foundation draintile inlets at similar height. When no rain, the pit is almost dry with not much underground water coming in, the pump is not running. When it rains the pump is cycling at reasonable frequency, if raining more heavily, the pump runs for 10s every 30s, until the incoming water start to back up in the pit and water level rises higher than the inlet pipe, that's when things start to go bad (happens once or twice a year). Water will then backed up at the grated channel and eventually enter the garage. I got some advise from drainage company that because of the water backed up inside the pit first, then backed up at the grated channel, it means that the bottle neck is the discharging capability rather than the inlet 4 inch pipe. What I need is to increase the discharge rate, so that the incoming water can flow freely (without backed up water in the pit blocking) into the pit.

I have got quite a few opinions, which are rather costly to me, from digging another pit at different location with another wiring and pump, to adding another pump in addition to my current setup and replace the entire discharging port with large pipes (including break through the cinder block wall to locate and replace the 1.5inch pipe goes out into the side backyard. A few concerns/questions I have in order to really pick a valid solution

1. From my description, do you feel that the problem is the discharging speed? I understand better solution is to reduce incoming water, for example, repair/waterproof the retaining wall to reduce he water from neighboring yard. My neighbor has already built a french drain system behind the retaining wall which helped a little, but I still see water pouring out from the retaining wall when it rains heavily. All my gutters were discharged through other pipes to the curb side and storm drain, and no visible overflow from the gutter (had guttergaurds) to the driveway run off.

2. How do I know if a pump is enough, for example, this 1/2 hp liberty pump has rate of 8400 GPH at 5ft, but the 1hp pump I got only has 7250 gph at 4ft. (curves from manufacturers attached), but requires much higher current/power than the 1/2 hp pump. The 1hp pump seems to have higher head according to the curves though. How do I compare this two pumps, if the max rate (speed at 0ft head)matters, does it mean that my 1hp pump is not as strong as 1/2 pump i have right now (because of different brands)? I ask this because it looks like the failure prone portion of most pumps are the float switch, I was planning to use a Hydrocheck H6000 high-lo electric switch with the pump until I noticed that the switch is rated at 13.8A while this 1hp pump is 14.2A rated (3/4 hp ones would draw less than 12A which can be used with this switch). I attached the current Liberty pump 's curve and the new pump I just got (circled out the 1hp and 3/4 hp ones). If 3/4hp is what I need, then I would couple it with the electric switch no problem.

3. Another advise is to reduce the 90degree turns in the discharging pipes and use 2 inch pipes until it is connected to the 4inch gutter discharge pipe that is buried and eventually goes to the storm drain curbside. My estimate is that there is not too much 1.5 inch tube after it goes out the wall and joint with the gutter pipe (have a rough idea where the exit from wall is but have not confirmed by digging), would it help my situation if I replace the exposed portion of 1.5inch pipe with 2 inch pipe without breaking the wall? Again I understand it is ideal to replace everything 1.5 inch before it's connected to the gutter drain, just coming from cost-effective angle.

4. If I put a more powerful pump in the pit (say the ihp pump listed above), how do I adjust the float switch to avoid over-cycling, especially when it only rains light to moderately heavy, which was handled alright with current pump) Should I let the pump turn on when water level is right below the inlet pipe since I notice that having water in the pit blocking the inlet seems to be reduce the inlet water speed quite a bit and cause water backup at the channel drain.
5. I'm restless about the pumping going bad for whatever reason, that's where the thoughts of more reliable non-moving electric switch came from. But other than that, do you think I need a secondary pump at all? Any other risk mitigation methods? Cheaper solution might be a utility pump with a flex tube either hooked up with the current discharge pipes somewhere or directly pump to street side? I will need to rewire another dedicated line from subpanel/backup generator for a 2nd pump too.

Sorry about such a lengthy post/repost, I'm trying the provide as complete information as possible for your suggestions. Thanks a lot

RE: Sump/sewage pump size for run-off ground water discharge questions.

1 1/2 inch pipe can handle no more than about 60 - 70 gallons per minute (say about 4,000 gallons per hour). if you want to maximize the flow rate, you will need to upsize your discharge line to at least 2 inch diameter.

the photo seems to show about 50 gallons capacity in your sump which should take about 1 minute to pump out. however you say that the pump only runs for 10 seconds. 10 second run time every 30 seconds seems too short. seems like your sump may not be deep enough and during heavy rainfall, your pump discharge is inadequate.

RE: Sump/sewage pump size for run-off ground water discharge questions.

Hmm, That's some pst alright and maybe not really one for a professional pump forum, but I'll give you a pass for today...

Any way a little more data if I can ask:

1) does your pump have a Non return valve incorporated in it?
2) What is the approx length of pipe before the pipe emerges into the open air?
3) When you get heavy rain does the pump run continuously? You mention 10 seconds every 30 then you start talking about the water level reaching the top of the pit?

Anyway I reckon your issue is the pipe, not the pump. The issue is head loss.
I think you have a static head of at least 8 ft from floor to where the pipe goes out the wall (does it go up any more from that last photo?)
With your current pump you only then have about 10 ft less for losses in the pipework. I reckon you're sitting about 60 gals/min

Those LE50 pumps appear to be very efficient compared to the other pumps you list which have less head and flow for the same input power.

But you're stuck with the issue of a realtively small sump and highly variable in flow which is very difficult to do with only one pump.

I think if you can increase your pipe size to maybe 3" then your existing pump will probably cope with a storm condition. 2" is better but still not great.

those pumps you show would be better because they are higher head but because of lower efficiency I don't think you'll get much more flow.

Or make the sump bigger to absorb the sudden downpour scenario....

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Sump/sewage pump size for run-off ground water discharge questions.

(OP)
@cvg, thanks for your reply.

One of the pix showed the inside of that pit, and as I mentioned in OP, I was a little concerned that the inlets of those pipes (the white pvc is the one catch water from the grated channel) plus the two black draintiles seemed to be low compared to other typical sump pit installation pix I've seen. When the pump cycles 10s every 30-40s, the water level in the pit is not too much over that inlet pipe, and would be discharged after the 10s cycle. If the water came in too fast compared to the discharging, I would start to see the water level rise above the inlet and pump would constantly running, that's when the grated channel area in front of the garage start to have water puddling. So I never really see the water level in that pit rise to over half of the height without having backed up at the channel and water start to enter the garage half way.

If it gets worse, the backed up water would enter the garage entirely, with 1 inch standing water, and the pit water level would maintain at high (rise slowly or maintain), until the rain gets lighter and water recedes. If keep getting worse, the water in pit would overflow and at that point, the standing water in the garage would be 2inch or higher.

My gut feeling of seeing this is that the sump pit's volume was not utilized efficiently (I think you want the inlet pipe higher up in the pit, so that the pump can have enough time to pump out water before it covers/blocks the inlet pipe, coz water flows into air is much faster than moving into a full tube of water) Did I understand the fluid mechanics correctly here?

I feel readjusting the pit seems to be a very costly project since the limited space there. But do you feel that I need to dig the pit deeper so that the relative height of the inlet pipes would be higher in the pit? Is it OK to have the edge of the sump pit/tub lower than the concrete inside that crawl space?

Also is increase the pump capacity (say getting a 1hp pump)+ maybe swap out all the exposed 1.5inch pipes right before it enters the wall, the easiest/cheapeast solution or i still need to pair it with a deeper pit?

RE: Sump/sewage pump size for run-off ground water discharge questions.

(OP)
@littleinch, thanks for bearing with my lengthy posts and all. I've been battling this for the past year after several trials and errors, inherited this problem without the previous owner disclosing it.

To answer your questions, if the non-return valve is a checkvalve I'm not sure the pump has a built-in one, but i think there is one check valve(the black thingy) in the discharge pipe (vertical portion).

For 2), if you are referring to the vertical pipe from the pump till it makes the 90degree horizontal turn, I would say about 3-4 ft. That pit is just a standard size trash can with a lid, so not a big one. And the pipe goes horzontally out from the block wall but not higher. based on the surroundings, my guess is it goes out the wall and tap into the 4inch pvc gutter drain, and outside that wall is the higher point of my side backyard and I belive the gutter drain then use the gravity to carry water into the storm drain curbside.

For 3), when the pump cycles 10s every 30-40s, the water level in the pit is not too much over that inlet pipe, and would be discharged after the 10s cycle. If the water came in too fast compared to the discharging, I would start to see the water level rise above the inlet and pump would constantly running, that's when the grated channel area in front of the garage start to have water puddling. So I never really see the water level in that pit rise to over half of the height without having backed up at the channel and water start to enter the garage half way.

If it gets worse, the backed up water would enter the garage entirely, with 1 inch standing water, and the pit water level would maintain at high (rise slowly or maintain), until the rain gets lighter and water recedes. If keep getting worse, the water in pit would overflow and at that point, the standing water in the garage would be 2inch or higher. During the whole time, pump is running continuously. Also want to clarify, the pump currently in the pit is 1/2 hp LE50 (curve is the 2nd one), the cheap 1hp one I got has the curve in the first graph (I thought the 1hp one has more head than the LE50, but has less max rate,or I'm reading it wrong?). I was trying to trial and error to see if a larger pump would improve the situation, since that maybe the easiest thing to start with, I'm also trying to see which is the key point of the solution (pipe size, pump size or both). So thank you for suggesting the pipe size might be more important than having a larger pump in.

RE: Sump/sewage pump size for run-off ground water discharge questions.

I think you understand clearly, the inlet is too low, the pit and the pump inlet is not very deep and the sump is not being fully utilized. making it deeper will be costly. installing a second sump tied to the first might be cheaper but still costly. Both options also require upsizing the discharge pipe improve the pumping rate. So start by upsizing to at least two inch diameter and cross your fingers that is enough to make the difference.

RE: Sump/sewage pump size for run-off ground water discharge questions.

(OP)
@cvg Is the 1.5inch in/out the wall portion critical to change if I replace all the exposed pipes to 2-3 inch? If my estimate is right, the remaining 1.5 through the wall until getting tapped into the gutter drain, would be 2-3ft or less.

Also, if the pump has 2 inch port, would 3 inch pipe cause the slowdown of water and the deposition/potential clog of the particles in the water?

With the sump pit as is right now , I'm concerned about the cycling issue with larger pump given the volume (water below the inlet pipe from channel drain) that it needs to replenish is relatively small, the big pump may cycle way too often (it may only need to run 4-5s compared to the 10-15s the current pump runs) when it rains moderately. Is that an issue without readjusting the sump? Currently I think the pump was set to kick in not too high above inlet pipe, so when it runs normal, I would hear the water dripping sound fading and then the pump start to run for about 10-15s, until the next time water level covers up the inlet (depending on how fast water comes in). Should that be adjusted to kick in higher? I feel it works when moderately rain, but when incoming water is too much too fast, the pump is not gonna be able to get it out and I would probably see a lot more overflooding from the sump.

RE: Sump/sewage pump size for run-off ground water discharge questions.

What are all those other pipes entering the pit??

More water from somewhere else?

what level does it start and stop at?

Can you sketch out a cross section view of this from the grating with some dimensions?

A larger pump would only help a little bit because you're basically maxing out the practical flow in your 1 1/2" pipe. If you double the flow you need 4 times the pressure loss.

A larger pipe should allow you to flow more so velocity wouldn't be an issue here in terms of sediment. It's going to be going fast enough

Unless your remaining 1 1/2" pipe is less than 10% of the total length then your pipe size upgrade might not see much improvement.Try to do it all - It's much better.

Basically though as you improve that capability your pit will pump out even faster when on low water flows, burning your pump out.

Your pit is simply too small so its up to you as to how to make it bigger. Maybe another two or three of those plastic drums connected together at the base??

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Sump/sewage pump size for run-off ground water discharge questions.

(OP)
@LittleInch

The two black draintiles seem to be some kinda of foundation drain at the house's perimeter, I don't really see too much water from them. There is a smaller pvc seems to be the AC drain which is also minimum, the big PVC pipe is the 4inch tube that's buried under the garage concrete connecting the grated channel in front of garage. I think currently the concrete is grated to make this pvc pipe the lowest point.

Here I drew an illustration of the cross section, the tub is a 20" inner diameter around the top but narrows down a little towards the bottom, 39" deep. The center of that PVC inlet pipe is about 22" above the tub buttom, so roughly at the center height (higher than I thought). I can't tell the pump starting water level right now since it's only raining slightly, but judging from the sound (incoming water flowing down to hit the water inside the sump fading), I'd say it's set at about that inlet pipe level, around 20“-24”,it stops at maybe 2-3" where I can see the float sitting at the bottom out of the water.

The discharging pipe: 38"(from pump up)-elbow-19"(horizontal)-elbow-7"(down to ground level inside crawl space)-33"-elbow-9"-elbow-87"(45degree up)-45degree elbow-11"-right angle elbow (where it exits the cinder block wall), there are two right angles elbow from the pump up then back down to ground level(I think can be eliminated?) to give space for the lid

RE: Sump/sewage pump size for run-off ground water discharge questions.

I estimate about 20 gallons or less is your useable volume, your sump is way too small. Cycling is currently a problem and increasing the pumping flow rate will not improve it. It will however allow your pump to keep up with higher storm flow to prevent flooding. the ultimate solution is to increase the useable volume of your sump

RE: Sump/sewage pump size for run-off ground water discharge questions.

(OP)
@cvg, If the discharging speed improves with larger pipe, can I set the pump starting water level higher to improve the cycling issue? I don't know what normally a sump pump's kick in water level is though, is it higher or lower than inlet pipes? Another question is what a normal sump size is, I checked online and a lot places are listing 30" deep, 18-24" in diameter as a routine basin, for example https://www.radonseal.com/pumps/articles/sizing-su..., this pit I had seems already larger or at least on par, of coz, my application is different than a regular "sump pump", but is it really way too small (if paired with appropriate sized discharging pipes).

The crawl space is really tight to fit another sump, so to increase the usable volume, either dig it deeper and wider or maybe add another sump with/pump at another location? Don't know which one is more costly though, and it will be on top of replacing the discharging pipes.

One landscaper gave an idea to dig a sump inside the garage (the right front corner inside, view from the door), and then extend the channel drain and connect it with the new sump with some underground pipe, then discharging straight up and penetrating the cinder block wall and tap into the gutter drain right outside that wall (which I suppose is the same the drain that goes around the back and connect to the current pump discharging pipe on the other side). Easier way is to have an external sump+pump, but freezing could be an issue, especially if we want to pump straight up to meet the gutter drain.

RE: Sump/sewage pump size for run-off ground water discharge questions.

Quote (ShinDiors)

If the discharging speed improves with larger pipe, can I set the pump starting water level higher to improve the cycling issue?

yes, that might allow the pump to run a little longer



Quote (ShinDiors)

what a normal sump size is

pumps are not normally sized to handle peak rainfall runoff rates for an entire driveway, they are usually for seeping groundwater and nuisance flows.

RE: Sump/sewage pump size for run-off ground water discharge questions.

OK,

Interesting post and issues so here's what I make of this.

You are working with a very large range of flowrates of water here which is nearly impossible to do effectively with a single fixed speed pump and a very small pit relative to the flow rate / pump.

Having looked more at the details of your system as it is now I think you are more likely pumping at around the 90-100 gals/minute mark so have about 15ft of head losses (static and friction) when your pit is full. Even replacing the entire system in say 3" pipe won't get you much more flow ( say 120 gpm).

Without out knowing the fall or relative invert levels of your intake pipe it's not possible to say if you should raise the high level point on your pit or not but I can't see it making more than a couple of seconds difference so I would leave it as it is.

So I would think you should try

1) Replace what you can easily of the 1 1/2" pipe with 2 1/2" or 3" pipe and leave the rest as is. See if this is "good enough" for the 1-2 times/year when you get surface flooding.
2) If not then the next best thing is to install a second pit next to the first with a cross over at a high level (above the inlet level from the drain)so that it only works if the first pump is being overwhelmed or has broken. You might think about moving your current pump into this pit and installing a smaller pump to cope with the more "normal" flows to stop this intense stop/start action which will be reducing the life of your motor as we speak. You probably only need something which does 20-30 GPM at 10 ft head. Just run at least 2" pipe and preferably 3" pipe from this new pump to give it the best you can. Then with the smaller pump you will probably have around double your current flow capacity.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Sump/sewage pump size for run-off ground water discharge questions.

(OP)
@cvg, thanks for the reply
@LittleInch Thanks for the reply and suggestions

You nailed the core of this problem, the wide range of flow rate vs single pump+smaller pit. Currently the 1/2 pump was put in with the mindset to deal with worst case scenario, but its on time each cycle probably was set too short to cope with the fastest incoming rate. I would probably see more flooding (both overflow from pit and water backed up and enter the garage) had I set the trigger level at higher water level.

I did a very coarse measurement, so the inlet 4inch pipe from the grated channel is roughly 23-24 ft, the height drop from entrance (at the channel) to exit (at the pit) is probably 20 inches or slightly less. I would see water pouring out fast when its raining heavily. I think the bottle neck might not be the incoming speed, but more with the water storage capacity and discharging speed.

I think there is some room for a 2nd pit in the crawl space (in front of the current pit) but could be very costly considering the narrow opening and hard to work condition. I would imagine you'd have to stand outside trying to operate a jackhammer then crouch/benddown to dig the hole.


Talked to at least four difference group of contractors (some are general contractors/handyman, some are landscaper/drainage/waterproof company), only a handful of original ideas but not once any measurement of the current capacity. There are currently two different proposed solutions at the table:
1. Adding a 2nd pit and pump, but originally it was brought up as an external pit/pump and discharging either with surface pipe to street side. But freezing could be a concern. This seems to be the least complicated/costly as it does not involve too much concrete breaking. (location is the yellow circle, it is the diagonal from the current pit) Variation of this solution is to put the pit inside the garage (red circled area) to avoid freezing risk, this would discharge straight up and penetrate the cinderblock wall and tap in the gutter drain right outside the wall at about ceiling level(should be the same gutter drain the current pump discharge pipe taps into as well. Shown in this pix).

I would like to have this pit to be the primary if that's the solution to go with, and leave the current sump and discharging pipe as is to save some cost. I have a spare 0.3 hp zoeller sump pump that I can put in the original pit, and use the Liberty 1/2 HP or the other 1hp pump in this new pit. One thing associated with this is how to divert the incoming water to this corner, since the channel drain and the concrete driveway is graded in a way that the PVC pipe in the channel drain is the low point for water to go. So the channel drain may need to be extended and regraded, which could be helpful to the garage door posts (currently both sides garage door posts are water damaged, and water flows along them from both sides, arrows shows the water flows direction).


2. Adding a second pump in the same pit, stack or parallel, with discharging pipes swapped to 3" pipe inside out. Two pumps will use the same 3" pipe (Y connected). There is only one drainage company mentioned dig another pit in the crawl space, simply because they thought the current tub may be too narrow for two pumps, not that they put in calculation of the current volume, pipe location, head loss etc like you guys helped me with here. This this also the company that tries to sell me the plan to spend 45k to replace the retaining wall and waterproof/drained behind the wall. Ultimately they are correct that the wall is failing and water from behind the wall (from neighboring yard) is contributing more than half of the incoming water especially when it's raining crazily heavy. Just don't have the fund to deal with that and also not sure if we would tear down and rebuild in the future (if rebuit, I would not want to have such a hefty retaining wall and lot height difference between mine and neighbor's, and will have space for a front load garage).

With all the additional info, do you guys have more suggestions which solution would be my best compromise? You both pointed out to swap the existing discharging pipes with larger (2 or 3 inch) and leave the rest (including the 1/2 hp pump?) as is and see how it goes. If this is not enough, I will have to use solution 2 right? Otherwise, I will basically spend entire cost of solution 2 plus maybe half of solution 1 (I think the pipe replacement might be more than half, coz it invloves digging and conrete breaking) all together. Also in my case, I'd probably really need a 2nd pump as a backup, although I have backup generator to mitigate power outage, can't help if the pump itself goes bad. A side-note, is it possible to leave a twist open inlet on the discharging pipe that I can drop a pump inside the pit in the case of emergency and discharge it with the existing pipe? Or maybe I should just go ahead put in a 2nd pump while at it? Any thoughts on the two pump configuration (I have a 0.3hp zoeller sump pump at hand (1.5" discharge port), 1/2 hp Liberty, 1hp off brand (both 2" ports). I read that if do parallel, two pumps need to be similar size/power, I then probably want to buy another liberty. What if stack layout, should I put big pump up or down?

Any advice?

P.S: We just confirmed and located the exit out of the brick wall for the 1.5" pipe at the backyard.

RE: Sump/sewage pump size for run-off ground water discharge questions.

Yeh, a world of pain and cost you're in there.

What's under that concrete slab in the top photo where the two black wires are? Can't understand why you don't saw cut the slab and then dig out a hole for the second pit?? why do you need to break it out?

Or could you not break out a hole in the floor of your garage on the line of the inlet pipe and insert a pit which you can grate over or drive over and insert your little 1/3 hp pump. Then when that overflows it flows into your existing pit which you've improved by making the pipes a bit bigger? So your red pit circle but in a different place. Far better than trying to dig up your gutter.

Getting two pumps in parallel is never easy and even "identical" pumps, one will be 60 to 65% of the total unless you're very fortunate.

I terms of existing capacity can you do some tests? Just open the top and when you drain a hose into it slowly measure the level it kicks off the pumps, level it stops at and accurately measure the time taken to reduce the level.

work out the volume then divide by the fraction of a minute it took to get GPM.

Do that a few times to get some consistent readings then come back and tell us. At least then you'll have some idea of what flow you might get from a properly designed pumping system

for option 1 just replace the pipes you can get at without digging or excavating - that's a days work if that. Best if you could replace the lot, but you're into diminishing returns there.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Sump/sewage pump size for run-off ground water discharge questions.

(OP)
@littleInch, thanks for the follow-up. The space you referred to actually is the room for a possible 2nd pit, it's just that the opening to enter that little crawl space is pretty small and low (it's a square cut out from the brick wall, with bottom edge 5inches off the ground, one pix in my OP showed that entrance) so any adult person would either have to sit/crouch outside and operate the tools to remove the concrete. Sorry for my ignorance, I thought to remove concrete you only use jackhammer so not sure saw is an option.

As for the location of "red circled", we picked that corner because of the ease of tap the discharge line (initially it was proposed outside the garage, but it evolves into the yellow circle inside for the freezing risk. There is a gutter drain accessible at ceiling level).

Also putting it in that corner has little interference to the normal use of the garage. On the other side of the garage, the only possible location outside the crawlspace is the corner where the lawn mower is (shown in the op's pix), but it's not on the line of inlet pipe which was place not parallel to the sidewall but with an angle), there is a door, part of the staircase in the way for pipe routing too.


My general contractor (who renovated my house and put in the liberty for me) would come for something else, I would ask him to swap out the pipes first if he can do it. Digging a 2nd sump definitely is not his thing though. He should be able to put in the 2nd pump in the pit, that's why I was trying to seek advice if the pumps I currently have can be repurposed while he is dealing with the pipes already. Again, we could swap the pipes first and see how it goes, but I definitely would need some advice on any backup plans if we are still in a single pit/pump situation. Prior to posting this, my plan was to have him put the 1hp offbrand with existing setup and trial/error, but then started to worry about pump failure/mitigation plan. It's almost freezing temp outside, but would rain in a couple of days, I will try to take a few timed measurements then and update back. Based on @cvg's estimate in post above, the usable volume is around 20gallon or less (pump is on when water rise at the inlet pipe level, so less than half of that 50gallon tub, minus the volume leftover when pump turned off), and about 10-15s tops, the pump would stop, so we are roughly talking about ~70-90gallon per minute currently. I'd probably need to observe (with almost freaking out mind) at the crazy rainstorm event to see the worst case's incoming flow rate. I agree that the sump is maybe too small for those events (when it start to backed up), say, if it only takes 10s or less for the pit to be filled to the inlet pipe level, then pump then has to be on 10s to remove it for the next fill up (ideally, I'd think the water level in the pit should be at an equilibrium at inlet pipe for any sump? Otherwise water flow is seriously blocked by the water body), increasing the pump power would only make it cycled even shorter which is worse.

I'd be interested to know what a "optimal" triggered on water level should be? Is it right below the inlet pipe (to avoid incoming water backed up at fastest rate/bad storm). But again, cvg got a valid point that "sump pump" is not speced to do this type of run-off water discharging, but more for the seeping/slower underground water.

I want to thank you both again, LittleInch and CVG for offering your insights. How much I wish that there could be a company/contractor that would really have the expertise to carefully evaluate the capacity and nail the core, offer and deliver solutions (or maybe I should've not gone to landscapers/waterproofing co/drainage co but some other specialty?)! None of the people I talked to pointed out that the sump size might be a problem. Only one backed his diagnosis with my described symptoms that the discharging rate is the cause of my water backed up, but not really talked about potential cycling issue if I improve the discharge but with the same capacity sump.

RE: Sump/sewage pump size for run-off ground water discharge questions.

A few more observations and comments. I was going to ask if occasional flooding of the garage floor was a serious concern but then I see the man door access, which I'm guessing leads into the house. So yes occasional flooding is serious and unacceptable.

Almost any modifications to the retaining wall would be extremely expensive. This might be self evident but fundamentally the ideal solution would to be to minimise the volume of water. I mention this for two reasons. Whatever your mental budget is, you may need to increase this $$ amount in order to avoid even evaluating modifications to this wall. Dont perform a half ar***ed job in the garage and still have to deal with water in the house. One of your photos appears to show downspouts from the roof feeding into a 4 inch pipe. Does this pipe lead to the sump?? If so, surely you could redirect this roof drainage away from the garage. You appear to have at least 7 feet of elevation to work with, so even 200 feet of drainage pipe affixed to the retaining wall should work.

You acknowledge that concrete removal is not one of your strengths. I agree with Littleinch that cutting out say a 30 inch square within the garage would not be expensive. The contractors who do this very often will do concrete coring as well. It appears to me that where your existing pipe comes thru out of the garage, you could easily core out a 3 , or even 4 inch hole in the wall, say about 30 inches above grade. Then replumb your 2 inch pipe with at least 3 inch pipe, or even 4 inch if future design confirms Littleinche's suspicion that 3 inches might be marginal. Install all the necessary Wyes etc at this stage to give you flexibility in the future. Dont worry about the cost of excavating a second sump at this stage..... you will only have to incur this cost if all the other preparatory work proves inadequate.

I might be failing to recognize some of your logistical difficulties here, but hopefully this gives to more to work with. And dont even think about two pumps in series... two in parallel might have some problems , but two in series will provide virtually zero increase in flow rates. A four inch discharge system should be able to deal with a 3 HP pump , giving additional flexibility going forward

RE: Sump/sewage pump size for run-off ground water discharge questions.

(OP)
Thank you, miningman for you reply.

Let me attach a sketch of the cross-section (view from the backyard). The sunroom and garage were addition added together, that downspout pvc you see goes underneath the deck at about the ceiling height (of the garage) then making a turn connected to the downspout on the other side, eventually goes to the curb storm drain. I have located the 1.5inch pump discharging pipe exit at that side of backyard and 99% sure that it taps into this gutter drain pipe (not sure how long it extends out from the wall though, hopefully not long). It is about 10inches deep at the backyard level, right outside that sunroom side wall/window.

I think my difficulty is maybe trying to find a contractor to do the whole project (from digging a hole to replace pipe and install pump), and several contractor we discussed in detail onsite ghosted on me afterwards without a quote.

My reading comprehension might be off, so when you said " Dont worry about the cost of excavating a second sump at this stage" were you also suggesting the need of a 2nd sump pit on top of the discharging pipe up-sizing, but not a 2nd pump (but how would the water be discharged out in the overflow pit)? Or you meant no need to go with solution 2 in my post,putting a pit at the other corner with a 2nd pump tap into the gutter drain? My thinking is that it may be easier (hence cheaper) for contractor to dig a hole in the open, compared to having to work their tool in that tiny opening of the crawlspace where the current pit is (my pix shows that opening), if either way I can't get away from having to get a 2nd pit (and a 2nd pump), I may save the cost of current pipe up-size (if the new pit on the other side being the primary with bigger pump and 2-3inch pipe), since I can use a smaller pump (for example, the 0.3hp zoeller i have as spare, which has 1.5inch port only), and use that original setup as the backup/overflow setup. From cvg and LittleInch's posts, it seems that my current pit setup has too little of usable volume (~20gallon), so even at my not-optimal discharging pipe, 1/2 hp pump cycles on too short. But if the incoming water is not much (only overflow level), I can afford to have a smaller pump for longer cycling on time.

If it's not crazily expensive to swap the discharge pipes, it will certainly be better to swap it still, giving me flexibility of using a larger pump in that original pit.
Looking at my record, I got quote of $3,600 to up-size all 1.5inch pipe and install a 2nd pump in the same pit. And they were saying this was the lower end price (if the digging is not too much in the backyard).

RE: Sump/sewage pump size for run-off ground water discharge questions.

A couple of other obvious things to check- make sure all the existing pipes are clear of debris, a partially clogged discharge pipe could be why your pump is unable to keep up with the extreme flow scenario. Hopefully this was already checked, just making sure. Check the pipe from the driveway grate to the sump pit also while you're at it, this should probably be a yearly maintenance item to keep the pipes clear of sediment and debris. Also as others have mentioned, there appears to be a second pipe draining into the sump, any idea what this is connected to? Have you ever seen water pouring out of it? If so, possibly this flow can be redirected elsewhere easily. I agree with everyone else that it sounds like a larger sump capacity is required, and probably larger discharge piping also.

RE: Sump/sewage pump size for run-off ground water discharge questions.

(OP)
Thank you keyepitts. All checked no obvious blockage, also other pipes do not contribute too much water if any.

@LittleInch Just want to follow up on the overflow sump adjacent to the current sump idea. You mentioned that the cross over should be above the current inlet pipe, I assume that this crossover pipe should sit relatively higher in the new sump pit unlike my current one right? So the new pit, (if I can still house a same 50gallon one) should sit relatively lower compare to the current pit (not higher as you mentioned), coz we want to use more volume in the pit before having to cycle on the new pump? Also I should be the larger pump in the overflow and use a smaller size one in the old pit? Since the discharge rate is improved, the current 0.5hp pump probably only need to cycle on shorter time to discharge this fixed volume of water, which is worse to the pump. Can I set the trigger level higher than the inlet pipe (but I'm concerend that it would cause water to backed up in the inlet pipe). Can you clarify a little more?

$all, another smaller reason I was leaning towards having the new sump in that corner (if I have to get another sump and pump) is that : related to this water problem, the run-off water from both front and back would always flow towards the garage door posts (shown in my pix above with arrows), so they are already water damaged. One solution of fixing that is to extend the channel drain (let it become a U shape) to cover the door poss/brick session) so that water would fall into the channel instead of hit the door post. Building the sump in that corner would probably need this extension of grated trench in order to channel it into the pit. It seems that this project (extension of channel drain) was too small for a lot contractors they don't even bother to respond. It may be a stupid logic here, please feel free to call it out.

RE: Sump/sewage pump size for run-off ground water discharge questions.

Without getting into the nitty-gritty of your post, the problem is not the ground run-off but the massive amount of water from your roof drainage, worthwhile calculating what this is likely to be during heavy rain.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

RE: Sump/sewage pump size for run-off ground water discharge questions.

(OP)
@Artisi, thanks for your reply. I disagree that the roof drainage is the major factor in this as all my gutter downspouts are drained with underground pvc to the curb side, and all my gutter has gutterguard and I have not seen water backedup and overflow from the gutter in rainstorms.

I think the core of this problem here is as @LittleInch mentioned, wide range of flowrates that is difficult to be efficiently handled by one fixed rate pump, also the usable volume being not sufficient. Currently this 1/2hp pump is cycling on for 10-15s tops to empty the volume that sets it off (est to be less than 20gal, so little less than half of the sump pit). Upgrade the discharging pipe may be able to improve the 2-3 times surface flooding situation, but would not help the cycling time (probably would worsen it if the float switch not changed). Better solution is to increase the usable volume of the sump (either upgrade the current size or have a 2nd pit) with the discharging upgrade, that way the pump can be set at higher water level switch on so that it runs longer each time, in the same time the extra water flowing in (at extreme cases) will have some additional sump volume to stay before causing backed up at the garage door area.

cvg and LittleInch both suggested upgrading the discharging pipe first, and hope that could cope with the occasionally heavy rain storms. That could be the cheapest thing to start, and if that works, my next question would be how to safeguard this system coz it's a single pump (although backup generator protected). My thinking of the "two pump-one pit" is more as a safeguard plan for the primary pump failure rather than relying on the additional flow rate. As you can see, this is currently the only way any run off water could be discharged, if the pump craps out in a heavier rain storm, it's nerve wrecking to even think about.

If discharging pipe upsize alone is not sufficient or get me stuck at short cycle time (which increases the single pump failure possibility), then I would need a 2nd pit plus a pump. I'm weighing where to set up the 2nd pit.

a. 2nd pit adjacent to the current pit
Pros:
  • can utilize current set up for the inlet water, so far all the driveway and grated channel were grated in a way to divert water into this inlet pipe.
  • maybe easier to wire up the 2nd pump
  • can take the advantage of the same upgraded discharging capacity
Cons:
  • More difficult to dig the sump pit compared to operation in the open area.
  • The only location of the 2nd pit would be in front of the current pit, and after that, there is not much room left, I'd think it would be ultra difficult to make any adjustment or maintenance especially for the original pit (currently if I need to do anything to the original pit, I need to ride on the square opening, one leg inside one leg out, no way for me to get my whole body inside and work on. I'm 5'11". If there is another pit in front, there will be no way for me at least to do anything with regard to the inside pit)
b. 2nd pit in the diagonal corner
Pros:
  • Easier to dig the pit
  • Shorter discharging head loss (plan to pump straight up for maybe 8 ft and tap into the existing gutter drain pipe that is buried right outside the wall
Cons:
  • Need additional work or adjustment to divert the water into this pit (such as extending the grated channel etc). However this adjustment may helped my water damaged garage door posts problem, one stone two birds.
  • Maybe more difficult to wire the power source (it's further away from my utility room)
  • Additional cost if the original discharging pipes still need to be upsized.
I hope this summarize our discussion so far.

RE: Sump/sewage pump size for run-off ground water discharge questions.

Would a higher head capacity pump make sense to better push flow through existing plumbing?

Ted

RE: Sump/sewage pump size for run-off ground water discharge questions.

You do also have a c which we haven't talked about much which is adding a second pump to the existing pit with a second pipe.

If you think this is an option then what I would do is swap out your existing pump for your smaller one using the same pipe.

Then suspend your bigger pump above the smaller one if you don't have room inside the pit for the two side by side but fit it to a new larger pipe. It should be pretty straight forward to core through that block wall and then out to the outside.

Then set the switch for the second pump higher than the first one by as much as you can, but at least 9 to 12".

You still might get some cycling when the flow gets too much for smaller pump, but overall the lower flow of the smaller pump should reduce cycling in more moderate rain conditions.

A bigger or second pit is better for sure but if it's just getting too hard / expensive then this is a viable alternative.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Sump/sewage pump size for run-off ground water discharge questions.

(OP)
@LittleInch, I'd think having to run another pipe out would be as expensive as swapping/rerun the existing pipe if not more (I think the new pipe would still be out from the similar height of old pipe and then connected to the same 4inch gutter drain that goes to storm drain right? or you were suggesting simply discharge out in the backyard). But worth asking when my General contractor comes. The stacking of two pumps scenario (but with Y into same upsized discharging) was the solution 1 with a quote ($3.6k). But your Option C here may re-purpose my 0.3hp zoeller (although it is a sump pump, not sure durability in getting this type of surface water) nicely, coz it has 1.5" discharge port matched the 1.5" pipes. But if the 2nd larger pump is triggered much higher, in the case of extreme incoming speed, the small one cannot cope with the speed, so water will rise up, covering the inlet and then the 2nd pump would kick in much later, by then wouldn't the water already fill the inlet pipe and causing backup at the grated channel? That has been my question all along, will the backup at channel happen if the pumps are triggered at level that's above the inlet pipe.

@miningman mentioned that the two pumps in series would not gain too much flowrate in the prior reply, but I guess that's when they discharge in the same pipe (not improving much even with a big 3" pipe?)

@hytools, swapping in an 1hp pump (the one I attached curve diagram) was originally my wishful thinking. As a matter of fact, it was a 1hp FQ sewage pump that was inside the pit when we had inspection (but not working). But it seems that this may cause worse short cycling if the sump pit only provides same 20ish gal to pump out.

RE: Sump/sewage pump size for run-off ground water discharge questions.

"were you saying to have the 2nd pump with separate pipe (leave the existing discharge pipe as is) and discharge out on its own"

Yes.

Running different pumps in parallel into the same discharge pipe isn't a great idea.

Still easier than doing a load of digging.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Sump/sewage pump size for run-off ground water discharge questions.

(OP)
Sorry to repost, I was editing my reply while you were responding.

@LittleInch, I'd think having to run another pipe out would be as expensive as swapping/rerun the existing pipe if not more (I think the new pipe would still be out from the similar height of old pipe and then connected to the same 4inch gutter drain that goes to storm drain right? or you were suggesting simply discharge out in the backyard). But worth asking when my General contractor comes. The stacking of two pumps scenario (but with Y into same upsized discharging) was the solution 1 with a quote ($3.6k). But your Option C here may re-purpose my 0.3hp zoeller (although it is a sump pump, not sure durability in getting this type of surface water) nicely, coz it has 1.5" discharge port matched the 1.5" pipes. But if the 2nd larger pump is triggered much higher, in the case of extreme incoming speed, the small one cannot cope with the speed, so water will rise up, covering the inlet and then the 2nd pump would kick in much later, by then wouldn't the water already fill the inlet pipe and causing backup at the grated channel? That has been my question all along, will the backup at channel happen if the pumps are triggered at level that's above the inlet pipe.

@all, can anyone tell me
1. Is 10-15s on each cycle considered "short cycle"? What is the ideal on time and off time each cycle?
2. What is the normal float switch on water level? My gut feeling is it should not be far away from the inlet pipe level other wise water would backed up in the inlet pipe (basically the pipe itself become water-full)

RE: Sump/sewage pump size for run-off ground water discharge questions.

Shindiors, I think you are focussed in the wrong areas. You are losing sight of the forest because of the trees. Almost everyone here recommends getting rid of the 1.5 inch pipe restriction..... only you can decide whether to go 3 or 4 inches. Forget about you spare 0.3 HP pump....... design a system you believe will work and procure the necessary hardware. You are an electrician.... the cost of getting power to another sump or pump must be trivial in the bigger picture. The cycling time of a pump can be designed/ accommodated when procurring the new pumps...probably a more expensive hi quality unit will give you what you need.

Given that previous owners have left you with a very poor design.. all rainwater flows back towards your garage door, I will reiterate that this may well become a $10-12,000 project, UNLESS....

I am not sure you have given adequate thought into intercepting rainfall before it hits the ground. Could you not install some kind of guttering low down on the retaining wall and divert the flow?? Have you considered re-locating the door to the house so the sill is about 8-12 inches higher than the garage floor.?? Is pouring an extra 3-4 inches of concrete on the garage floor worth thinking about?

And dont be too hard on your potential contractors. As the owner/client, it is up to you to determine what you want. They can advise, but do not reject their technical advice simply because it might cost more than your'd assumed

RE: Sump/sewage pump size for run-off ground water discharge questions.

ShinDiors:sorry missed the point on the roof drainage going to the kerb.

The comment from LI - if considering using 2 pumps for such a small sump - it is preferable to install 1 pump above the other.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

RE: Sump/sewage pump size for run-off ground water discharge questions.

A problem indeed.

Consider running a raised concrete lip down the driveway. There are countless high-tech concrete patching and machine-mounting high strength polymer based concretes that will stick like glue to clean existing concrete. Section off most of the driveway so only water that exceeds this new lip actually makes it into the current grate. Realizing that the water coming down the driveway is only a few millimeters deep the little curb doesn't need to be too high. Perhaps an inch?

Then where the little curb makes the deepest puddle due to your driveway grade, saw out the concrete for a LARGE sump, perhaps 36" or 48". This is out in the open so a conventional concrete saw can be used or even a skillsaw with a masonry blade if you're handy(desperate) and willing to trade hassle for labor costs.

In this design include where to get the power to run the new sump. The power can be a 3/4" pvc conduit cut in the concrete to the nearest garage wall where a transition onto the wall and regular conduit to the house supply happens, so include concrete sawing to encompass that.

Now you need to provide for the pumped out water. Saw the concrete for that exit. This time make it 3" pvc from the start. Sawing concrete outside, standing up, with sawing equipment, is nearly trivial as compared to the close corridors stuff being considered.

Leave the existing poorly done scheme to handle only what the added concrete gutter misses. Change nothing on it.

Grate/sump stuff is everywhere at any landscaping/sprinkler supply places. Concrete is cheap.

Don't waste your time trying to make the %#($& existing setup work right.




or get arty



Keith Cress
kcress - http://www.flaminsystems.com

RE: Sump/sewage pump size for run-off ground water discharge questions.

The issue over filling the inlet pipe isn't one which should bother you. If the inlet into the pit is covered there is no real impact to the flow capacity.

Only when the level in the pit equals the bottom of the inlet pipe in your grate will it start to back up. The only reason this isn't done is when the inlet is constantly submerged but stationary you can get some silting potential, but your max flows are such that they will sweep out anything. No need to be concerned.

So you can set the high trip / start point above the inlet level into the pit.

~So your questions
1 - 10-15 seconds for a 3-400 W motor may not be too bad, but motors like running, not starting and stopping. The start current is often 4-6 times what the running current is so frequent starts both heat up the motor and also stress it and the starter contacts which could reduce the life cycle. Difficult to be precise about this, but 10-15 seconds of operation every 30-60 seconds is just not a great design.

2) Up to you - normally set at a level which doesn't result in anything bad ( in your case the level reaching the bottom of the grate.

To test this just turn your pump off and slowly fill the pit from the gutter until you can just see water in the bottom of the grate / channel. then mark this level on the pit and adjust your float point accordingly to be just lower than this max level.

As to where you should or could run the new pipe - that is again in your hands - we can't really see where else you could go but you have a free hand to do whatever is cheapest and easiest. You don't have to follow the same route as the existing just so long as it goes somewhere and doesn't get much higher than ground level in the back yard.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Sump/sewage pump size for run-off ground water discharge questions.

(OP)
@all, thanks so much for all the great discussion. A lot to chew on for me. Will update once I have a clear pathway. Much appreciated it.

RE: Sump/sewage pump size for run-off ground water discharge questions.

Yeh, been kind of fun.

TBH these forums are meant for larger industrial pumps and not "domestic" issues and we don't want too many, but it was sort of technical so you got away with it, plus lots of responses and pictures.

Hope to hear back about what you decided to do and if you have any more technical issues with your pumps or pump performance.

LI

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Sump/sewage pump size for run-off ground water discharge questions.

Think about a self-priming floor mounted pump located at a convenient spot to suit, this could be sized to suit the inflow - auto level controlled for on/off, although delivery pipe sizing could still be a problem.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

RE: Sump/sewage pump size for run-off ground water discharge questions.

(OP)
@LittleInch, just to update and a few more questions

We are going with the option C, so adding a separate 2inch discharging line and connect it to the Liberty LE51A, and repurpose the Zoeller M53 with the existing 1.5inch pipe (will remove some uncessary right angle turns).

I recently noticed that unlike what I estimated before, my current pump is trggered on about half way (definitely below the inlet pipe into the pit), so it only pumps out actually less than 20gal (maybe only 10gal) each cycle-on and it only runs for about 8-9s.

Now the 0.5hp liberty is raised about 5 inches from the bottom (sitting on two pieces of stones). whereas the 0.3 hp zoeller on bottom. How should I set up the float switch on the Liberty. The Zoeller is a vertical switch I think it would triggered on more and hopfully handle the moderate rain by itself. My question is if I should still set the liberty's float (even after it's raised up physically) at about the inlet pipe (with your filling water test) or I should leave it as is?

Thanks a lot.

RE: Sump/sewage pump size for run-off ground water discharge questions.

Raise it as high as you can go ( the inlet pipe level sounds Ok to me)

Then as the rain flow increases and your smaller unit gradually operates continuously then you can still afford to leave the bigger unit as reserve.

As you note once it kicks in then it is likely to cycle quickly unless the flow really gets high, but you should maximise the running time.

I would also set the off switch at a higher (say 6") level than the smaller pump "off" level switch so that it keeps running all the time when the bigger unit kicks in.

As we've said many times this isn't a great system and really needs a bigger sump, but the longer the bigger pump can run for each time the better.

Hope it all works as we think it should!

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Sump/sewage pump size for run-off ground water discharge questions.

Just throwing this out as a concept (skimmed the thread and didn't see it, maybe it was already mentioned) but you could get two flowrates with a single pump if you have a solenoid valve and two discharge pipes.

Single discharge for normal operation, would keep the pump left on the curve and flowrate down so you don't have really fast cycle times.

Add a "high high" level switch to the sump that opens a solenoid valve to a second discharge pipe for increased flow out, so the single pump would now discharge through two sets of pipes. Just tee it off as close to the pump discharge as possible and use the largest pipe that is feasible between pump discharge and the T (or Y, whatever fits.)

Do some quick match to see what friction loses you get with the existing pipe, maybe you want another discharge of the same size, or maybe it should be larger or smaller than what you currently have, depending on the pump curve.

Check "normal operation" (single discharge pipe) pump efficiency to see if it's acceptable, or if it will hurt your electrical bill.

This may or may not be easier than just adding another pump, but something to consider.

RE: Sump/sewage pump size for run-off ground water discharge questions.

(OP)
@LittleInch. Actually went ahead dig out all the 1.5inch and now replaced it with 4inch pipe, so the two discharging pipes (1.5 and 2) now discharge into a 4 inch pipe underground.

Now the problem with the pit, since it is a trash can, my contractor did not find a good way to suspend the larger liberty too high up, so it was on two pieces of stepping stones (I'd say only raised about 3-4 inches from bottom), and because of the tighter space (now two pumps with two pipes), there is no way of extend the tethered float on the liberty pump without it bumping into other inlet pipes and stuff. We did a test with the max level of water (using the method you mentioned, fillng the pit until water backed up at the grated channel), the big pump alone ran about 10s until it stopped (where the small pump can still trigger on to continue pumping). However, I can't set the tethered float to that level without the risk of having it stuck/bumped into other stuff).

With the current trigger level, the big pump alone (we haven't tested two pumps together as we are figuring out the additional wiring with the 2nd pump) only ran 2s till it stops, which worries me, and it could be shorter had the two pumps were pumping at the same time. My guy could not come up with ways of raising the big pump higher, and the space is also a problem of having a long tether (so that the triggered on water level is higher).

We are hoping that we won't be seeing the two pumps on too frequently, but my back up plan is to bypass the liberty's tethered float and use those electroic hi-lo switch which does not run the risk of float being stuck. Before I go that route, any other ideas of setting up the bigger pump water level higher?

RE: Sump/sewage pump size for run-off ground water discharge questions.

Shin diors

Ok, that's one way to do it.

Very difficult to add anything as these are all things you need to see with your own eyes, but have you looked at suspending the bigger pump on wires or cables from a couple of beams spanning the pit?

As to the float switch I can't see the issue so again can't offer much but I would do everything you can to increase the time the larger pump runs for so if it needs new floats or other activation switches then so be it and scrap the built in version.

1-2 seconds operation is no good at all.

Good luck.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Sump/sewage pump size for run-off ground water discharge questions.

(OP)
@all
Came back to do a final update and close it out.

To sum it up, we dug out all the 1.5 inch pipe in the backyard (about 15-18ft, just by me and my dad) and eventually located where it jointed with the 4inch pipe. We replaced all with 4 inch pipe. Inside, the existing 1.5 pipe was modified a little to reduce some right angle turns, and then the 0.3hp zoeller was repurposed as the main pump with the 1.5inch pipe, with the 0.5hp Liberty raised about 3-4 inches above as backup/2ndary pump with 2inch pipes separately. Two outlet pipes were connected to the new 4 inch pipe outside, in the backyard. Had to use Hi-Lo sensors for both pumps to optimize the run time, now the small pump run about 45-55s each time depending on incoming flowrate. I've only seen one time (about 3inch rain) when the small pump had to continuously run, but did not kick off the big pump (I was at home, so I manually turned on the big pump just to see how fast it can do the job). With the two pumps on, i'd say it's pretty beefy now at discharging water. So far with 2-3inch rain (max rate was about 0.5-1ch/hour), it seems that the small pump can handled it no problem. I'm not sure if this can handle the 4inch/hr rate we had last year, but should be alright for most of the scenes.

One thing regarding the hi-lo sensor, I recommend the hydrocheck sensor compared to the Chinese knock off brand Briidea. I made a mistake to use Briidea for the big pump since it had a higher current rating, however it did not take into the pump starting current pike into consideration, and would trigger the overcurrent mechanism which stopped my big pump when it's needed. The Hydrocheck one does not have this problem.

I want to thank you all for bearing with my "off-topic" thread here and giving me ideas/feedback. Much appreciated it.

RE: Sump/sewage pump size for run-off ground water discharge questions.

No problem - Great to get some good feedback and updates and your posts were errr comprehensive...

Goes to show that it is rare for the pump to be wrong - it's all about matching pump to system and optimising.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

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