Very Slow Pressure Loss

[Ron64]

I just had a 1200 gal cistern installed with a submersible pump. I have a 20 gal pressure tank set at 30-50 in my basement which puts it about on the same level as the submersible. What I am seeing is that the pressure tank seems to pump up fine and shut off at about 48 psi on the gauge. If I check the gauge in a few hrs without using any water it will drop 2-4 psi. It continues to drop at a slower and slower rate until it reaches 30 psi in about 48 hrs. Note there is no check valve immediately behind the pressure tank. A friend suggests that because of the lack of head pressure in the cistern that it's nothing to be concerned about because it is most likely just pushing the water back into the cistern at an extremely slow rate and wouldn't be noticeable if under normal operation. I'm concerned that I may have a leak somewhere underground. I don't want to start digging if not needed, help?

 

[Reach4]

I just had a 1200 gal cistern installed with a submersible pump.

Tell us how your system differs from this:

You have two submersible pumps; one down the well, and one horizontally in the cistern, right?

The one in the cistern is a 1/2 HP pump with what -- a 15 GPM rating? The pump in the cistern only has its built-in check valve?

You have a valve after the pressure tank that will shut off water to the house. When you shut that valve, the pressure loss continues?

I suspect your friend is right. Normally with your 15(?) GPM pump you would want a bigger pressure tank. Your pump run time is probably way under a minute.

 

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[Ron64]

Tell us how your system differs from this:

You have two submersible pumps; one down the well, and one horizontally in the cistern, right?

The one in the cistern is a 1/2 HP pump with what -- a 15 GPM rating? The pump in the cistern only has its built-in check valve?

You have a valve after the pressure tank that will shut off water to the house. When you shut that valve, the pressure loss continues?

I suspect your friend is right. Normally with your 15(?) GPM pump you would want a bigger pressure tank. Your pump run time is probably way under a minute.

That pretty much describes it except I'm not certain of the Gpm rating for the cistern pump but you are correct that it fills the 20 gal pressure tank in less than a minute, (probably just under 30 seconds to be more accurate. So you're saying you wouldn't be thinking there is a leak somewhere between the pressure tank and the cistern / well?

 

[Reach4]

So you're saying you wouldn't be thinking there is a leak somewhere between the pressure tank and the cistern / well?

That is my thought. You describe the rate of pressure loss dropping out of proportion to the reduction in pressure. I would suspect the built-in check valve leaks some water back into the cistern. It may be that you could add a separate spring loaded check valve at the output of the pump to stop that.

Your pressure tank probably should have been about 3 times larger. If you had that, you probably would never have noticed the behavior.

 

[Ron64]

That is my thought. You describe the rate of pressure loss dropping out of proportion to the reduction in pressure. I would suspect the built-in check valve leaks some water back into the cistern. It may be that you could add a separate spring loaded check valve at the output of the pump to stop that.

Your pressure tank probably should have been about 3 times larger. If you had that, you probably would never have noticed the behavior.

I caught the issue because I am able to isolate this water system. I understand your point on a larger pressure tank but why do you say I wouldn't have still caught the same problem all be it at a much slower rate? Would I still have seen the pressure drop at 1/3 of the rate now with a pressure tank 3 times larger? Is there a way to determine the head pressure in the 1200 gal tank? If so I guess I'd rest easier if at some point I let the pressure tank get equal to or less than the head pressure and then didn't see a drop on the gauge. What is the expected rating on the check valve in the pump as far as holding "check"? I guess after spending a considerable amount of money I'm surprised that my pump will have to cycle daily to account for back and forth flow but more so want to be 100% certain I have no leaks, ya know? I do appreciate all of your input and I'm hoping to get some remedy from the contractor eventually.

Can you explain your comment, "You describe the rate of pressure loss dropping out of proportion to the reduction in pressure.". I'm not understanding what you are saying? Thanks, I really appreciate the feedback.

 

[Reach4]

I caught the issue because I am able to isolate this water system. I understand your point on a larger pressure tank but why do you say I wouldn't have still caught the same problem all be it at a much slower rate? Would I still have seen the pressure drop at 1/3 of the rate now with a pressure tank 3 times larger?

My thinking is that the check valve is seating a bit with time, so I was thinking that the leakage might take longer than 3x. But still, if it was 3x, few people would have noticed cycling at 48 hours let alone 144 hours.

If so I guess I'd rest easier if at some point I let the pressure tank get equal to or less than the head pressure and then didn't see a drop on the gauge.

It is 4.33 PSI per foot. So no way that things would equalize.

I am not a pro. I don't know what the expectations should be. Somebody may have a good recommedation for a check valve to add at the pump output.

 

[Valveman]

It would be ideal to fix the check valve in the pump. But this just being a cistern pump, adding another check valve before the tank will keep water from flowing back to the cistern.

 

[Smooky]

How do you know it is not a leak such as a bad toilet fill valve or flapper? Could be something simple like that.

 

[Ron64]

How do you know it is not a leak such as a bad toilet fill valve or flapper? Could be something simple like that.

Def not a leak in the house because I have the main feed shut off.

 

[Ron64]

It would be ideal to fix the check valve in the pump. But this just being a cistern pump, adding another check valve before the tank will keep water from flowing back to the cistern.

I agree, it's a brand new pump...Installer said he plans on putting a check valve immediately behind the pressure tank and additionally I requested he perform a pressure test on the underground line right through the new pump install. I appreciate all the comments and will certainly follow up once complete so possibly someone else can benefit from my problem.

 

[Reach4]

I agree, it's a brand new pump...Installer said he plans on putting a check valve immediately behind the pressure tank and additionally I requested he perform a pressure test on the underground line right through the new pump install. I appreciate all the comments and will certainly follow up once complete so possibly someone else can benefit from my problem.

Would there be a problem in putting the new check valve at the pump?

I am thinking that what you call "just behind ..." I would call "just in front of ..."