Shallow Well Lawn Irragation pump cycle problem

[lfmgtc59]

I inherited a shallow well lawn sprinkler system that was disfunctional. After a lot of effort it is now up and running... almost.

Setup:

9 well points on 1-1/4" pipe (5 of the wellpoints are 1-1/4", the remaining 4 are 1")
The wellpoints are 13' deep with approx 5 - 6 feet of water.
There are check valves at the top of each well point
Well points are approximatly 10' apart

The pump is a Sta-Rite DS2HE-103 (all seals have been replaced)
Main inlet line is 1-1/4"
Main outlet, and the lines to the valves are 1"

On the outlet side I have a fitting (a) to allow me to add water / pressure to the system and just downline from that a valve to be able to isolate / shutoff the main line to the valves. There is also a pressure cut off switch just on the outlet side of the pump.

There are 9 valves.

If I pressurize the system by connecting a hose from the city water to the outlet side (a) the entire system with valves off will hold 40psi pretty much indefinitly even after the city water is cut off, so it appears there are no bad check valves and no leaks out to the valves.

There are two issues:

1. It takes about 20minutes for the pump to begin to make enough pressure to actually run the sprinklers - Is this normal?

2. Once the cycle has run and the valves shut the outlet pressure reaches 40psi the pump shuts off, but immediatly the pressure drops past the cut in pressure of around 20psi and the pump begins to go through a very short cycle... this continues until I kill the power to the pump, then pressure immediatly drops to 0.

Can anyone help me out on this, I have some ideas, but don't want to cut the system up trying them when I'm not sure whether or not they will work.

Any assistance is much appreciated.
Thank You!!

Lee
lfmgtc59@aol.com

[LLigetfa]

I think I need a check valve on the outlet side and to place the pressure switch immediatly downline of that, so that the pressure in the outlet side is maintained until a valve opens, pressure drops and the pump kicks in... Is this right??

No. You stated the pressure switch hangs off the side of the pump. A checkvalve on the outlet would isolate the outlet pressure and the pump would come back on.

If you want to prevent pressure from backflowing to the inlet, you need to put the checkvalve on the inlet of the pump, not the outlet. I doubt that will solve your problem though. No pump should take 20 minutes to make enough pressure to use unless you have an extremely large air charged storage tank.

I wonder... with multiple intake sand points, what would prevent the pump from drawing one down more than the other and suck air?

[lfmgtc59]

Thanks for the reply

... let me clarify

The pump manual specifically says not to use a pressure tank as this presents serious risk of explosion, so there is not one.

At present the flow is: Well point ->checkvalve (at each well point) -> 1-1/4" pipe -> pump -> 1" reduction -> Pressure switch & gauge -> valve with hose attachment -> manual shutoff valve -> main 1" feed pipe to valves

What I proposed was Well point ->checkvalve (at each well point) -> 1-1/4" pipe -> pump -> 1" reduction -> gauge -> valve with hose attachment -> checkvalve -> Pressure switch -> manual shutoff valve -> main 1" feed pipe to valves

I used the manual shutoff valve when I was troubleshooting leaks in the system to isolate the inlet and outlet sides.

I suppose it is possible for the system to pull some air with the multiple well points, but the pressure is pretty steady through 70 minutes of operation. If I run the system an additional 20 minutes you can begin to see fluctuations in the pressure and hear some air flowing through the valves.

However the real issue is after the valves shut and the pressure cut off of 40 is reached. That is when the cycling starts and as I say goes on until I cut the power.

[LLigetfa]

The pump manual specifically says not to use a pressure tank as this presents serious risk of explosion, so there is not one.

If the pressure switch shuts the pump off at 40 PSI, where is this serious risk of a rupture? With the pressure switch set so low, and if the pump capacity exceeds the consumption, in the absense of a pressure tank, short cycling is inevitable. No checkvalve on the outlet will solve that.

What is the max pressure that the system can safely handle? As you increase the pressure, the pump will produce fewer GPM so the pump will be less likely to exceed consumption.

Maybe valveman will come along and suggest a tank or CSV/tank combination to reduce the cycling.

[lfmgtc59]

I agree with what your accessment on the pressure tank, I don't see how the pump could possibly develop enough pressure to explode, but not being a diy'er on this I figured I would follow the directions.

I have been out doing some more checking...

It appears that even with the check valves at the well points, the 1-1/4" feeder pipe the well points are attached to is this morning near dry. The pump maintains prime (there is water in it), but the lines feeding it are basically dry... I thought the check valves were supposed to stop that.

This is why the 20 minute wait for pressure, only today I had to "fill" the feed lines back to the well point check valves in order to get the pump to draw.

The system still maintains 40psi when pressurized, so it does not appear I have developed any leaks...

So where does the water go and how do I fix it??

Signed Perplexed

[lfmgtc59]

Additionally...

If I fill the feed lines using the house water I can build up 40psi in the entire system. If I then close the manual valve to the main outlet line that feeds the sprinkler valves, and bleed of pressure and water via another valve on the outlet side, as the pump is running and making pressure on the outlet side, I can hear bubbles coming up through the feed lines from the well points...

If I shut the valve I am using to bleed pressure of with the bubbles continue and the pump continues cycling if I shut off the main feeder line the pump and pressure stablize and shut off.

It is almost as though when the suction in the feed line reaches the point of opening the check valve the air at the top of the well point enters the system and the water in the system is running back into the well point... that is the only place I can figure air would be entering the system...

Any experts out there willing to give me the benefit of your experience?

[valveman]

Without a pressure tank, you have nothing to maintain pressure after the pump shuts off. Just the check valves closing means a little water has to go backwards to do that, and you don’t have a tank to supply that water, so the pump comes right back on. The tank would also supply water back towards the check valves. So if there is a leak between the check valves and pump, you wouldn’t lose prime. Your pump will have to come back on when the tank is empty. The tank maybe able to supply a small leak for days or weeks before the pump must start.

I can’t imagine a pump that comes with a pressure switch attached NOT having a pressure tank. That is just crazy advice. Get a pressure tank!

You also probably have a leak on the suction side. But the pressure dropping as a tank drains to the leak will help you find the leak.

[lfmgtc59]

valveman...

I appreciate the advice and the explaination - Like I said I inherited the system which was not working at the time... so I'm not sure if the pump came with a pressure switch or not. The hand scrawled instructions I found in the valve control box had the first and last step of running the system as turning on and shutting off the breaker, so my guess is that it never worked right to begin with...

Anyway - Where would you add the pressure tank into the system?

Current arrangement: Well point ->checkvalve (at each well point) -> 1-1/4" pipe -> pump -> 1" reduction -> Pressure switch & gauge -> valve with hose attachment -> manual shutoff valve -> main 1" feed pipe to valves

How would I determine the size of the pressure tank?

Thank You

Lee

[LLigetfa]

To quote valveman, there are two kinds of checkvalves, those that leak and those that will eventually leak. A checkvalve needs pressure to maintain the seal. You cannot expect a checkvalve to hold in the absense of pressure.

Even if the checkvalves don't hold at the sand points and the water falls back, that doesn't explain the air in the collector pipes. The air has to be coming from somewhere. I'm not saying you don't need the checkvalves, because you do. They act as ratchet stops so that as the pump goes through spurts of suction/no suction, the gains it makes don't fall back.

As for a tank, I would put it as close to the pump discharge as possible and I would mount it higher than the pump. I would not use a bladder tank, just a free air tank without air volume control. The tank will act to bleed the air during start/prime, and the water in the tank will aid the self priming during start.

I don't know how much pressure the pump can produce nor how much it can safely tolerate. I couldn't find a manual on your exact model but the manual for a similar model makes no mention of how much pressure it can produce or tolerate. None the less, an air over water tank will help reduce pump cycling but what you really need to do is tune the demand to the supply, meaning don't close off more than the pump produces at 40 PSI.

[lfmgtc59]

Based on my tests the peak pressure this pump generates is about 45-48 psi when it first kicks on. The highest pressure it seems able to maintain over any period of time is right around 40 +/- 2.

A couple of questions:

I am familiar with the operation of a bladder tank as I had a house that utilized one when I was on a spring fed water system, however, I am not familiar with a free air tank.

What size tank am I looking for?

Should the tank be empty when hooked up (full of air) or water?

Will I need a way of draining the tank as I required with my bladder tank?

... Guess that was three questions.


Thank You

Lee

[LLigetfa]

Since the tank really is just to absorb fluctuation in pressure it would act more like a giant water hammer stop, so size is not all that important. I'd go with one that has around 5 gallons total volume. It would be full of air to start and the air would compress allowing water into the tank as the pressure builds. If it were to ever waterlog which I doubt, you would need some way to drain it or some way to pump air into it. More than likely, it would accumulate enough air on its own and surplus air would just go out with the water.

[valveman]

I would use a bladder tank. A 20 gallon size tank will hold 5-6 gallons of water. This size tank is large enough if you match the zone size to the volume of the pump. With that type of pump you can actually increase the pressure switch setting until the pump continues to run as long as there is a couple of GPM being used. Which kind of makes it work like a CSV.

You shouldn’t need a bladderless tank to deal with the air. If the pump still gets air after the tank is installed, you need to find and fix the leaks in the suction. Otherwise you could draw in air and lose prime while the pump is running. Which would burn up your pump. Losing prime while the pump is running is much more possible after installing the pressure tank. When it gets down to a couple of GPM before the tank fills, it is much easier to draw in air than water, and the pump loses prime. It doesn’t do that now because you are always pumping max flow. At max flow the small air leak just mixes with the water and you never notice it. At minimum flow the air will come in easier than water, and you will lose prime before the pressure gets to the shut off point.

After adding a tank, there should be no spurts of suction/no suction or you still have a problem.

[lfmgtc59]

Hey LLigetfa / Valveman:

You called it absolutly correct!! :-)

Ok, I added the tank... I had a neighbor with what looks to be an old 2 or 3 gallon tank that I hooked up. It actually works pretty decently. The system seems to start at 20psi and shut off at 40psi correctly with just a couple of cycles. It runs at between 24 and 36psi with the sprinkler system in operation with initial drops down as a new valve system opens up. There seems to be a lot of crud coming through, so the heads are clogging, but I guess that is just the result of it sitting for almost 5 years.

It holds around 26psi when it shuts off.

Based on what I am seeing I think the bigger tank you suggested would be a good investment. The local Lowes smallest tank is 7 gallon with a bladder. Do you think that would work Ok as long as I set the initial pressure in the tank at around 23?

Thanks again... it feels really good after what I have been through getting this up and running to see it actually work correctly.


Lee

[LLigetfa]

Looks like valveman and I disagree on the style of tank. Sure, a bladder tank will work to reduce cycling but if properly precharged, a bladder tank holds no water at 1 PSI. On impeller pumps, I like to have a reserve of water above the outlet. When starting the pump from zero, this "head" of water helps to purge the air yet drops back to the pump to aid the self priming.

Back in my youth, I worked with a lot of gas and diesel powered impeller pumps on pipeline construction and learned how to get them going faster than most anyone else. It looks like in your case, your could use the city water to put a head of water in the tank so perhaps it matters less. Bladder tanks are easier to find at big box stores.

As for crud clogging the sprinkler heads, don't most setups have large Banjo filter screens?

[valveman]

I like to have a reserve of water above the outlet. When starting the pump from zero, this "head" of water helps to purge the air yet drops back to the pump to aid the self priming.

OK! I see exactly what you mean. We use to keep gallon jugs of water sitting in the well house to prime with. We even had a bladderless tank. There was just a check valve between the pump and tank or we could have used that for priming as you said. Removing that check valve would have probably saved me filling about a thousand jugs of water.

But like you said, he has a garden hose from another water source. So I still think the bladder is best for this one, and as long as the pump doesn't cycle running the smallest zone, a 7 gallon bladder tank more than sufficient.