Gravity feed and Break Pressure Tank Help
Gravity feed and Break Pressure Tank Help
(OP)
Looking for some help on a gravity feed greenwater effluent line. I am new to these threads finding them while searching key words on the web. I work in the dairy effluent pumping business designing systems for farmers. Now I have been asked to design a gravity feed system which is outside what I have dealt with before. I have a HDPE lined pond with a 160mm drain pipe out the floor of the pond. There is 5 metres of head above the outlet. the outlet is 365 metres above sea level. I need to get this down to 60 metres above sea level. The pipe line will take a path down the hill that is 3.3 kilometres in distance. There is no power available along this pipeline. I would like to use 90mm alkathene with a 77.5mm ID, it is 8 bar rated. after reading some of the threads on break pressure tanks Im thinking of constructing 4 break pressure tanks, one every 80 metres of elevation drop down the line to 130 metres of elevation which should leave 70 metres of head pressure above my 70 m3 tank at the bottom. Not fully knowing about break pressure tanks, is this idea a sound way to get the effluent down to my irrigation equipment. I look forward to hearing back from big and little inch and all the others.





RE: Gravity feed and Break Pressure Tank Help
It sounds like a reasonable way if you're limited on pipe you can use - Looking it up alkathene is MDPE or PE80??
Your issues as I see it are:
what are the properties of this stuff - "greenwater effluent" doesn't mean much to me - does it have solids, does it have fibrous materials?
A 90mm pipe isn't very big - what sort of flow rate are you thinking of? The drop is a 1:10 slope on average which might be enough under gravity, but have you checked.
How you control this line and how you start / stop / control is the key. Without power you are looking at fluid powered valves, but these might clog internally or in the control piping.
Iff there is unlimited storage at the end point and you can accept a whole line fill and the contents of the ponds then you might be able to just flow from one end to the other via the break ponds / tanks without risk of overflow. Please advise what the flow regime is - continuous, start stop / needing to be controlled?
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RE: Gravity feed and Break Pressure Tank Help
As long as the slope continues downward at a relatively constant slope, you can use a gravity line. Without a break tank of some sort, if you valved off the flow at the end of the line, you would over-pressurize the pipe with 305 meters of water head.
It will also be necessary to install air releases along the line, otherwise, the line will become air bound.
You should be able to get 12.9 l/s of water at the outlet.
RE: Gravity feed and Break Pressure Tank Help
The drop is very close to 1 in 10 and is an almost constant slope as it goes down apart from 3 small rises before going down again. Once the entire system is connected to the pond exit pipe it will remain open to the bottom and under pressure at all times. The line that goes in will be trenched and buried. Every 100 metres of pipe length I will be connecting one of our steel 2 way steel hydrants with a gate valve on the inward flow leg. This for me is just a safety feature should any section of the pipe be damaged in future by diggers or machinery then they will have an isolating point every 100 metres. The exit pipe to the pond currently has a 150mm slide valve with a large cantilever handle on it, the pond is 2/3 full. What I would like to do is have a line to the 70 m3 tank at the bottom of the hill where we will be installing a progressive cavity pump to then irrigate out to the surrounding land.
the line going down the hill will always be open and under pressure back to the pond.
Ideally I would like to be getting about 10 L/s flowing into the 70 m3 tank. This might even be a 110 m3 tank. I have no knowledge yet about break pressure tanks but want to learn as fast as I can. I will be guided by your direction as to how many break pressure tanks we install.
I have seen some rough pictures of these tanks. Some have a ball cock on the inflow inside of the tank. Some had a pipe entering the tank and a pipe exiting the tank and no ballcock.
Excuse my ignorance on this subject but if I have a break pressure tank where the flow races in under pressure, swirls around the tank then exits out the other side and continues down the hill, is this a break pressure tank. Does the pressure coming into the tank not then pressure the tank to the same level and in turn pressure it directly out the tank. Or does this merely act to slow the speed of the flow down.
Regarding the comments from bimr, thank you for your help and anymore, I have planned again to put our steel two way hydrants on any high spot with a Europa swing check valve on the hydrant bridge. We usually always take the spring out, this is how I was planning to purge the line of any air when it was being filled the first time.
www.hitechenviro.co.nz
Getting to the bottom of this line, the feeder pipe will enter the 70 to 110 m3 open lid sump. This will need a ballcock arrangement in the sump to stop the flow when it is full. Will I need a break pressure tank quite close to the sump to lower the pressure on the ballcock.
On the safety side of this problem which is an environmental disaster waiting to happen is, what happens if the ballcock breaks for any reason. Do I split the incoming line into 4 and have 4 ballcocks to limit the possible flow should one cease to work. I can have the electrician wire up a high pond level alarm as well if that is a better solution.
If the break pressure tanks are the answer to this system then I would really appreciate some help on their design, how many and size. My apologies for being long winded, it is frustrating not having any knowledge on this. Thanks.
RE: Gravity feed and Break Pressure Tank Help
RE: Gravity feed and Break Pressure Tank Help
You said..... “4 break pressure tanks, one every 80 metres of elevation drop” and “ MDPE PE100 8 bar pipe is the most common pipe used here for effluent lines. It is cheaper than the MDPE 75mm 8 bar pipe.” I haven’t run any numbers here, several of the other guys have those types of calcs. on the top of their heads, so I’ll leave that to them. But, a couple things come to mind here, those pressure break tanks can’t be cheap, what with construction, including foundations, the tanks and all the extra piping. Then there are also any problems and ongoing maintenance of the tanks, whatever that might be. Why not eliminate the four tanks and just use a pipe, fittings and control devices which can tolerate the pressure at the various elevations as you go down the hill. Changing the pipe size or wall thickness as you go down hill. Put an energy dissipating device at the lower outlet to control the outflow into the lower pond. Better yet, put a small turbine at the bottom of the pipe line to generate enough power to at least control operate your control systems on the line and any valves, etc. The power would be there as long as the fluid was flowing. You are proposing an expensive, more complex system just so you can use some cheaper pipe. Maybe penny wise and pound foolish.
RE: Gravity feed and Break Pressure Tank Help
RE: Gravity feed and Break Pressure Tank Help
A similar situation occurs in deep level mining where diesel has to be gravity fed to underground tanks to fuel the locomotives. Mines can be kilometers deep and the piping would have to be uneconomically strong. The problem is overcome by eliminating all underground valves and feeding from a batch tank on the surface.
It would be better to put your effort into extra screening at the source tank and doing a bit of extra trenching to avoid high spots and just letting the line run at its natural capacity. With the slope you have, air removal would not be a problem. You will get velocities in excess of 2 m/s and this will be more than adequate to flush the air out.
Katmar Software - AioFlo Pipe Hydraulics
http://katmarsoftware.com
"An undefined problem has an infinite number of solutions"
RE: Gravity feed and Break Pressure Tank Help
Richard A. Cornelius, P.E.
WWW.amlinereast.com
RE: Gravity feed and Break Pressure Tank Help
You can also use pressure reducing stations rather than break tanks.
RE: Gravity feed and Break Pressure Tank Help
RE: Gravity feed and Break Pressure Tank Help
RE: Gravity feed and Break Pressure Tank Help
http://cdn2.hubspot.net/hub/230272/file-728537112-...
http://www.cla-val.com/documents/pdf/E-90-01.pdf
RE: Gravity feed and Break Pressure Tank Help
RE: Gravity feed and Break Pressure Tank Help
Let me summarise where I think this thread is up to / going.
This system really is quite small which I think is being missed sometimes here. with your 90mm PE pipe, my estimation is that you have about 16m3 inventory in your pipe length of 3.5km.
Whilst your route picture is nice, what you need to develop from that is a fairly accurate profile to decide where to place your tanks if that's the way you go.
I think you have three main options
Plan A - Install your system as you described. What you need to do is try and get the first section to be the highest head loss per unit length so that this becomes the bottle neck in your system and so on down the line by a margin of 3- 5%. You can do this by judicious selection of the break tank location or perhaps adding a certain length of reduced size pipe. That way you can install a relatively small tank - say 3-5 m3, and just let the system run. As the flow capacity out of the break tank should exceed the flow in, the tank should run empty unless something happens to block flow. Then you have two options - either have someone shut down the inlet and then accept you might have a small spillage or install a simple float system to shut off flow if the level gets too high, but normally is wide open. If you don't want this option the install the float control valve but you may still find that some tanks are emetpy and some full as it is difficult to get the head loss per unit length exactly equal between sections and even a small discrepancy in capacity over time will lead to the tank filling or emptying.
Plan B - Install with the pipe you describe but in a single length. This works so long as the fluid flow is continuous. If you then have a blockage or flow ceases from the lower end then you could significantly exceed the design pressure and you have a burst pipe. Hence this system really needs no valves along the route and hence you always need to maintain an ullage or spare tank of 16m3 so that when you stop flowing in, the line can drain down. Optionally you can install fluid powered pressure regulating valves like those bimr says - just be careful to get ones which accept non potable water.
Plan C - Install higher strength pipe able to withstand full static pressure if the bottom valve is turned off.
Only you can really determine which is most suitable, what level of risk is there about potential spillages and the overall cost of installation and operation.
Your idea about valves every 100m is not required and would lead to high expense for little benefit. Your route maps shows you're not in a place where people would go and dig this up and more valves equal more chance of leaks. If it is damaged or needs repair, just shut the top valve and let it drain down.
If this is to be spread on the fields then I can't see why you would go for anything more complicated than the simple gravity system but pease let us know how you decide to go.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Gravity feed and Break Pressure Tank Help
I look forward to any comments on this design.
RE: Gravity feed and Break Pressure Tank Help
You just need to ensure you can get flow equal to 1m/sec or more to sweep out air and avoid any silting up low spots.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Gravity feed and Break Pressure Tank Help
RE: Gravity feed and Break Pressure Tank Help