Shallow Well Pump Problem

[Cranky One]

Hi,

I have a 1hp, centrifugal, shallow well pump with a pre-charged air bladder water tank that is used for lawn irrigation. A couple weeks ago the PVC pipe for the intake side split. I replacedd it and the new one also split. I noticed that when the pump turns off, high pressure water sprays out the intake side until the water tank is emptied (I have it to run at 40 psi). Before I bother trying to install yet another replacement, is this operation normal? I have a back-flush valve on the line to the shallow well so their is no back-flush back into the well. Has an internal seal let go in the pump? It is a Myers HJ series pump.

Thanks for any assistance

[Harry K]

There has to be a leaking seal or pipe for water to 'spray out' from anywhere. I assume you are talking out of the pump itself. If the water is not spraying out around the screwed in pipe fitting, then it must be a seal. The proper installation (and you must have one) is for a foot valve on the end of the drop pipe in the well. That keeps the drop pipe and pump full of water when the pump shuts off. Some people also install a checkvalve between the pump and tank but that is redundant.

Harry K

[Andy]

Andy comments:

Well, one solution would be to install an additional check valve on the inlet side, backwards, so that any positive pressure there would blow off, just like a pressure safety valve. It would need to be on a tee, ........ and NOT in "series" with your foot valve.....

If you have an actual problem in your pump, you might want to get it fixed. But in my sprinkler system (fed from a lake), when the pump loses it's prime once in a while, I just hook the OUTLET high pressure side to the city water, and it forces water thru the pump into the inlet (suction) pipe and restores the prime. Unles the pump has a built in check valve, it will allow reverse water flow......

When the pump turns off, the outlet line has pressurized water in it. This will leak back thru the pump and bring the INLET pipe pressure up to some positive level. This also helps to seat the check valve at the end of the inlet pipe. Some pumps have built in check valves, some don't. Mine doesn't , so I can get away with priming it in the above manner......

Remember, the suction pipe never sees high pressure. No pump can "suck" more than 33 feet, and that is a negative 14.7 psi. So inlet pipes are not designed to be thick for positive pressure, but rather just thick enough not to collapse at negative pressure...... So, if you have a MOTHER pump that is putting 40-50 psi into the outlet pipe, it well might blow out your suction pipe......You could use a thicker suction pipe, tho..... just a few ideas..

Good luck..

Andy in Eureka, Texas

[Harry K]

Sorry but you are wrong. The inlet (suction pipe) in the well will always show system pressure when the pump isn't running if there is no check valve between pump and tank (normal installaltion).

Harry K

[Andy]

Sorry but you are wrong. The inlet (suction pipe) in the well will always show system pressure when the pump isn't running if there is no check valve between pump and tank (normal installaltion).

--- Harry K

Andy replies:

I don't disagree. But a check valve, mounted backwards on a tee, will bleed off the pressure . That means the total system pressure will drop to the point where the check valve opens, probly about 1 psi..... This ain't theoretical. Been there, done that.

Perhaps you misunderstood how the additional check valve was installed on the inlet....... Think of two check valves in PARALLEL. Both are at the END of the pipe, where it is below the water level, at the foot strainer. One allows stuff to go one way and the other allows stuff to go the other way.... When the pump SUCKS, water comes in one valve and the other seals shut. When the system BLOWS, the water goes out the second valve, while the first valve seals....

In this way, the pump can be primed just by attaching water under pressure (house spigot) to the OUTPUT side of the pump...When water starts coming out the 'bleeder" check valve, the pump is primed. And this system can be left in place.

I use it at my house on the lake, to pump lake water, where the pump and intake is located several hundred feet from the house..... I don't want to run "down there" to mess about for an hour on those few occassion when I lose the prime..... I just "tee in " house water " to the pipe at the house for a minute, and "VOILA", pump is primed........

Andy in Eureka, Texas (Registered PE in Texas, retired and inactive )

[Cranky One]

All, Thanks for your inputs. Got the problem solved with a beefier inlet pipe and new primer/cement. Lawn is happy again.

[Harry K]

There has to be something I'm not following here. If you have the installation as you describe it with just the two check valves, the system will dump all system pressure as soon as the pump shuts off. There would be nothing stopping the water draining back into the well from the tank. You would need an additional (third) check valve between the pump and tank. You would also loose prime every time the pump shuts off (if it is installed above water level and is not a self-priming pump).

I used to run an irrigation pump with nothing but the footvalve. That was easily primed by running water into the outlet pipe just like you say you do without any additional checkvalves.

Harry K

[Andy]

There has to be something I'm not following here. If you have the installation as you describe it with just the two check valves, the system will dump all system pressure as soon as the pump shuts off.

--Harry

Andy replies: Yes, we are both on the same page now. In my system, I use it for a sprinkler system and , if I mount the backwards check valve at the foot strainer, the system would drain back and lose its prime every time, just as you say. I was trying to simplify it,

--- a shame I can't make a simple sketch on the newsgroup.

In effect, my "reverse" check valve (which releases the sytem pressure) is put onto a tee right at the pump inlet, AND elevated a couple of feet ( 1 foot - 1/2 psi ) higher than the pump. Now, the entire outlet pipe will drain down until the water in it is at the same height as the reverse check valve. That way the suction pipe remains filled, with a couple psi in it to help seal the check valve at the foot. Sorry that I was inaccurate in my explanation. I had thought that the method and technique would be obvious, but I guess I must have mixed up the explanation...

Remember, the system will drain (depressurize) until the head in the system is the same as the head of the elevated reverse check valve. In a sprinkler system, it's non critical. If you have a tank system, you have to make allowances for what you want to happen.

Some people put two NORMAL check valves in the intake suction pipe -- one at the pump inlet and one at the foot valve. I don't like that since I have a big drop between the pump and the foot valve, and the increased tension in the second check valve seems to really cut down the amount of suction lift I can handle. I'm not sure why, but it seems to be a LOT worse than with just one check valve. I mention this just for reference, and that other designs I have seen have cautioned against two normal checkvalves in the input line. I guess they had the same problem (grin). They didn't say why, either.....

Again, I am sorry I wasn't clear in my explanation. A picture would be worth a thousand words here.

Andy in Eureka, Texas

[Harry K]

Aha! Now I follow you and it makes sense. I have seen the 'two check valves on the inlet" before but only when the original footvalve has failed and they attempted to fix it with the second one.

I can't understand why two valves would cause a decrease in the lift either other than possibly pipe/fixture flow restrictions. Rule of thumb is that a simple suction pump will draw from about 26 ft (near sea level).

Just curious here: Why do you want the system pressure to bleed off every time? Not that there is anything wrong with it but...

Harry K

[Andy]

I can't understand why two valves would cause a decrease in the lift either other than possibly pipe/fixture flow restrictions. Rule of thumb is that a simple suction pump will draw from about 26 ft (near sea level).

Andy comments: That rule only works if the pump is of the type that will literally pump air. My particular pump, which cost 39.00 for Harbor Freight, doesn't do squat with air, and can't suck the water up. So I have to keep the line from the foot valve to the pump impeller full of water. It works pretty good, then. I have no explanation for the double check valve prohibition, and have not conducted experiments. Perhaps it is an old wive's tale, and something else was happening in my system that causes the effect..... Heck, once I got it working, I quit worrying about it........ I am getting old.... (grin)

Just curious here: Why do you want the system pressure to bleed off every time? Not that there is anything wrong with it but...

Andy replies: That was a response to the original poster , who was finding his inlet pipe was bursting. It was theorized that the system pressure, when his pump stopped, got back to his inlet pipe . Since an inlet pipe does not have to have much thickness, ( 26 ft of head is aboutg -13 psi max) , it was suggested that the pipe was not strong enough. He could either put in a stronger pipe, or bleed off the pressure.....

Andy

[Harry K]

The 26 ft rule applies to all suction pumps even those with full inlet pipes. The "theoretical" maximum is around 33' (sea level) but pipe friction, pump efficiency, etc. knocks a bunch off of that. There are some that are self priming and I am not sure about how far they will suck with air in the lines. 26' is just a rough rule of thumb though.

Harry K

[thetiler]

I was breaking off outlet fittings on my pump every few weeks. Turns out the pump would move or "jerk" some each time it cycled, which would eventually stress out the PVC.

I just installed a new pump and this time I anchored the pump to the ground so there is no movement when the pump turns on and off.

PVC is pretty resilient but like aluminum it can only take a certain number of stresses back and forth at the joints.

thetiler