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

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

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

(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 underneth/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)matters, does it mean that my 1hp pump is not as strong as 1/2 pump i have right now (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 burried and eventually goes to the storm drain. 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, would it help my situation if I replace the visble 1.5inch tubes with 2 inch pipe without breaking the wall? Again I understand it is ideal to replace everything 1.5inch before it's connected to the gutter drain.

4. If I swap 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) 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.

Sorry about such a lengthy post, 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.

(OP)
Forgot one question,in my situation, I'm paranoid about the pumping going bad for whatever reason, that's where the thoughts of more reliable non-moving electric switch comes in mind. 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?

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

suggest you re-post this in the pump engineering forum. unlikely that geotechnical engineers will be able to solve your pumping and hydraulics question

pump engineering

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

Without a doubt, get rid of the 1.5 inch restriction. However rather than using 2 inch as a replacement, use 2.5 inch or preferably 3 inch. It appears that you dont have that much 2 inch pipe in the system. Replace all that wherever possible with 3 inch as well. This will give you an immediate large flow increase that the pump can deliver.

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

(OP)
@miningman thanks for the reply. I heard both pros/cons from using smaller/larger pipe than the pump's discharge port, please correct me if i'm wrong

Using smaller pipe than port
Pro: increase pressure of the water stream, so it would shoot higher/further, in my case it could be beneficial although my estimate is this pump would only need to pump the water to the exit point on the wall, and then the tube goes horizontally meeting with the gutter drain 4inch PVC (everything goes by gravity after that point)
Cons: more friction so worse discharging speed. Also would create back pressure to pump, bad for the life?

Using larger than port tube:
Pro: less friction, so more volume discharge rate
Cons: Speed of discharging water would reduce in the larger pipe, so the particles in the water may deposit/clog in the longrun?

I was advised to use 3 inch pipe only when planning to put two pumps in that pit using a "Y", coz when needed, two 2 inch discharge port would benefit from the larger pipe.

I think most of the exposed portion of this dicharging pipe is 1.5inch.

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

(OP)
@LittleInch The paranoid side of me couldn't help asking this: Should I also tie up the Zoeller M53 (small pump)'s vertical float and use the electronic hi-lo ones instead. We had a moderate rain event yesterday for about 2-3 hours, 0.3 inch -ish. The small pump ran 5.7s each cycle and it takes about 90s ish (at the flowrate then) to kick it back on. Based on Zoeller's spec, it's on-off level is 7.25"/3", so about 4.25" height of volume (non adjustable). I can use a high-lo pair, say, to set it to start at about my inlet pipe level, which should increase the "on" time a bit. I think the "max" level I can afford before it backs up, is a couple of inches higher than that which I can set as the "on" level of Liberty (big pump). I can keep the "lo" level for both pumps to have the big one stop first.

The cost of the high-lo sensor pair isn't cheap compared to the Zoeller pump's price (30-40% depending on the sensor brand), and my contractor kept advising me not doing this since the pump's built-in switch is working alright so far. Not sure if it's worth doing it now with the Zoeller pump. Thoughts?

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