Water Hammer?

Hi, I'm a new guy here but have visited this forum many times! I have gleaned much helpful information here as I come across well / pump related problems.

I currently have a customer with a 4 inch submersible well with a water hammer condition upon pump shut-off. The well is 100' +/- in depth with a 30' pumping water level. Pump is set on 1-1/4" pvc and I believe is a 1HP 20GPM nominal (although I have not pulled the pump). The tank is a 80 gallon (equivilant) captive air tank. The well is in the front yard and the tank is about 100' away at the rear of the house. The pressure switch is located in the tank Tee and pipe from well head to tank is also 1-1/4" schedule 40 pvc. Water hammer is noticable in all supply piping including the drop pipe.

What do you all think? I'm assuming that I (likely) have a check valve problem but get confused when I try to visualize what happens when one check valve leaks and there are two in the system. I can viualize that if the check valve at the pump leaks then the water above that point will go to a negative pressure while the "upper" valve holds tank pressure................ However, if the "upper" check valve leaks and the one at the pump holds then I'm thinking maybe this would explain the hammer upon pump shut-off.

The whole check valve discussion is a can of worms I know but I'm a fan of one check valve at the pump although a check valve a the surface is required here (at least on new installations). Would I have any problems with the afore mentioned customer set-up with a single check valve at the pump? What about the pressure switch bouncing ............. any pearls of wisdom?

Many thanks
Teme

If I am reading your diagnosis correctly, then you have it backwards. At the moment the pump turns off the entire system is at the same pressure. If the top check "leaks" there is no effect because the water between it and the pump is still at system pressure. BUT, if the bottom one leaks then there is an immediate pressure differential between the two sides of the upper check, and that WILL slam the valve closed, because up until that moment it was open to allow water flow.

Thanks for the explanation................. I'm going to work on this tomorrow and I'll see if the pump check is holding.

Teme

I have a hard time visualizing HJ's scenario unless it is about a "hammer" at pump START. The water column is in forward motion when the pump is running, and no matter if the pump check leaks, stopping the reverse flow of water at the surface check rather than the pump check should have no effect other than a very slow leak down of pressure in the drop pipe.

HOWEVER: anyone with a plain tank with an "air maker" has a pump that starts as if the pump check valve leaks! I dont see any hammer in my systems running that way. I have yet to see an adequate explanation of why that is so from the one check valve school of thought. Perhaps the column of air in the down pipe cushions the start shock.

If the pump check holds pressure [or not] it may be just plain old water hammer - high flow pump that is shut off in an instant. That pump could be pushing 25 to 30 GPM at shut off. Try a few runs with the outlet throttled back near shut off moment, Or perhaps a higher shut off setting. Thats faster than putting a pressure gauge on the well side or bypassing the surface check.

For those of you that subscribe to the one check valve theory, its pretty easy to pull the guts out of one and keep the inspector happy. But note that the pump MFG's show check valves every 200' down a drop pipe. Go figure.

Finally, the pressure switch should not or cannot "bounce" if the surface check is good and there is air in the tank.

You are thinking like an electrician not a plumber. IF both checks are working properly or even if the top one is defective, the water IS flowing forward when the pump stops. At that point the bottom valve closes rapidly from the weight of the water on top of it, but even if it does create a momentary hammer it will not be detected or noticed. In the meantime the upper one is in a stable water environment so it just "floats or swings" closed by the action of gravity. NOW however if the upper one works and the bottom one does not, the dynamics change. Now the water between that valve and the pump create a suction as it drops through the lower check. At the same time the system pressure upstream of that valve creates a back pressure which "slams" it shut. Between the suction before the valve and the pressure after it, the upper check valve will close with a sudden, and violent action, causing the "big bang".

HJ is correct here. This is a very common occurrence. You should not have two checks on the line. The check at the pump is enough. If there is one at the inlet of the pressure tank, get rid of it and your hammer will go away.

Thanks for all the comments;

HJ, I'm probably a moron but if the check valve at the surface (right at the tank) is OK then I can visualize the pipe "below" that going on a vacuum thus creating a big differential at the surface check valve. However, if this surface check valve is holding it seems like the hammer would occur mainly near the tank junction. In this case the hammer is audible all the way down in the well.

Ballvalve brings up the scenario where maybe this water hammer is due to a big flow rate being stopped suddenly. This pump is producing at least 25 GPM. The pressure gauge is broken (probably due to the hammer) and so cut-off pressure may be too high!

I see plenty wells set up like this one (maybe not as far between the well head and tank though) and havent seen this problem so bad before!

Also, I like the gutted valve suggestion................I'm going to try it. Heck, it's not that unusual to find a check valve that has gutted it's self.................usually at the surface. I can't recall finding a leaking check valve at a submersible.

Finally, I'm going to deal with this well tomorrow and I'll try to post my findings.

Went to the location today and began by troubleshooting the checkvalve in the pump. I didn't pull the pump but ran it until it kicked off and cut the pipe near the wellhead. Pipe stayed full. Went to the check valve at the tank tee and removed it ........... it was bad. Replaced bad check valve, pressure switch and defective gauge, checked pre-charge in tank............ 27psi. Ran pump, set pressure switch to 30/50 and water hammer still there!

The pipe from the wellhead to the tank tee is about 80' +/- and has several 90s and it's clamped to the floor joists. Evidently the problem is not new............ the clamps have dug into the pipe where it has been sliding an inch or so each pump cycle for a while.

Finally, just to see what would happen I put a line check at the well head................. no improvement.

Any ideas?........... I think ballvalve is right..............maybe this water hammer is just due to the layout of the pipe and the substantial flow rate of the pump stopping suddenly.

Since the pipe run is so convoluted and has some damage I'm thinking I"ll replace the run of pipe and re-locate it away from the framing (maybe lay it on the ground..........it's a raised house) and at least they won't hear the bang!

TS

Wally Hays said:

HJ is correct here. This is a very common occurrence. You should not have two checks on the line. The check at the pump is enough. If there is one at the inlet of the pressure tank, get rid of it and your hammer will go away.

Click to expand...

Hi Wally, I think the setup reproduced your scenario since the checkvalve at the tank was bad and the one at the pump is holding. Do you think the routing of the pipe and being attached snug to the framing could be the culprit?

Thanks,
TS

How far is the pressure switch from the tank?
If it is more than two or three feet, it needs to be moved closer.

A liquid can not be compressed and there for will not cause a bounce,
the tank is the only place that should have air, and the only place a bounce could occur.

The only other thing that would cause a bounce, is a restriction between the pressure switch and the tank.


Travis

Hey Travis,

The pressure switch is about 2 feet from the tank (P/S is mounted on the check valve via. a 1/4" pipe nipple). Also, my question about the pressure switch bouncing may have been misleading. What I meant was could the pressure fluctuate enough (to cause the P/S to open again) on pump shut-off if I was relying on a just the check valve in the pump. That seems like a possiblity with a long run of pipe....... maybe not........ I don't usually mount the tank so far from the well head. Also, our wells here are mostly shallow (200' or less) with pumps seldom set deeper than 100'.
Thanks,
TS

The distance between the well and tank makes no difference. It could be two feet or two hundred.
The only thing that really matters is the distance and restrictions between the switch and tank.
The check valve the the switch is on should be taken out. With a bladder tank there should be only one check valve at the pump,
or at least under the water level.
With the two checks working correctly, they can fight each other and cause the hammer.

I have seen checks in the pump not seal right away like it should,(Mostly from older checkvalves) and cause a short pressure drop in the pipe, and cause a short chatter when cutoff pressure is reached.
I read where you said the check at the tank was bad.



Travis

hj said:

You are thinking like an electrician not a plumber. IF both checks are working properly or even if the top one is defective, the water IS flowing forward when the pump stops. At that point the bottom valve closes rapidly from the weight of the water on top of it, but even if it does create a momentary hammer it will not be detected or noticed. In the meantime the upper one is in a stable water environment so it just "floats or swings" closed by the action of gravity. NOW however if the upper one works and the bottom one does not, the dynamics change. Now the water between that valve and the pump create a suction as it drops through the lower check. At the same time the system pressure upstream of that valve creates a back pressure which "slams" it shut. Between the suction before the valve and the pressure after it, the upper check valve will close with a sudden, and violent action, causing the "big bang".

Click to expand...

Must be nice to be "boss hog" and delete my posts because they show you dont have any understanding of what water hammer from a pump is. You are thinking like a plumber, not a pump and hydraulics man, and I find it disgraceful that you can insult me and I cannot post a reply. This is becoming a pathetic and lame forum that will soon only be populated by the bullies and narrow minded "tradesman" that have not read a book on their trade in 25 years. No one with any sense would call a plumber to work on a well system in this area.

If you want to delete some posts, read some of the latest - they are pathetic in their complete lack of basic understanding of water hydraulics.

Turns out that this well only had ONE check at the well because the surface one was broken. That makes fun of those that say you cant have 2 checks.

STILL waiting for that PLUMBERS explanation of why all pump handbooks reccomend check valves each 150 or 200 feet down the hole.

If a pump is at 5000' and the standing water level is at 30', the pumping calcs are done from 30' - there is no "suction differential" in this well.

Put a CSV or a dole valve on this well and the hammer will go away.

But this post will go away soon enough, because moderators do not like to be shown their mistakes.

Sixdays said:

Went to the location today and began by troubleshooting the checkvalve in the pump. I didn't pull the pump but ran it until it kicked off and cut the pipe near the wellhead. Pipe stayed full. Went to the check valve at the tank tee and removed it ........... it was bad. Replaced bad check valve, pressure switch and defective gauge, checked pre-charge in tank............ 27psi. Ran pump, set pressure switch to 30/50 and water hammer still there!

The pipe from the wellhead to the tank tee is about 80' +/- and has several 90s and it's clamped to the floor joists. Evidently the problem is not new............ the clamps have dug into the pipe where it has been sliding an inch or so each pump cycle for a while.

Finally, just to see what would happen I put a line check at the well head................. no improvement.

Any ideas?........... I think ballvalve is right..............maybe this water hammer is just due to the layout of the pipe and the substantial flow rate of the pump stopping suddenly.

Since the pipe run is so convoluted and has some damage I'm thinking I"ll replace the run of pipe and re-locate it away from the framing (maybe lay it on the ground..........it's a raised house) and at least they won't hear the bang!

TS

Click to expand...

Did you replace the check at the tank? You should have removed it altogether.

ballvalve said:

STILL waiting for that PLUMBERS explanation of why all pump handbooks reccomend check valves each 150 or 200 feet down the hole.

Click to expand...

That is because the people who write those handbooks have never been in the field and seen the problems that multiple check valves cause. And on paper, if one check is a good thing, then multiple check valves should be extra safe. Just another one of those counter intuitive things.

Hi Wally,

I did replace the checkvalve at the tank. In hindsight I agree I should have crippled the checkvalve at the tank.

Eventually I have to go back and run a new water line from the well head to the tank.............................. I'll take that opportunity to make some changes.

Thanks,
TS

ballvalve, I may be showing my ignorance but what is a dole valve. Also, I've seen the CSV at a couple trade gatherings but haven't tried one yet.

Thanks,
TS

Valveman will fill you in on the CSV, but it might likely solve your water hammer, or as a test try and throttle down the flow into the tank to just 1 or 2 GPM at the time of switch cut-out. you might kill the hammer and not need to change the pipes. If the pipes still hold water after years of pounding, they must be in good shape.

Dole valve reduces flow in a hydraulically correct way and have rated flow rates. Typically used to make a pump output match the wells production, they might not be right for your customer if he at times needs that fulll flow. The CSV ont he other hand would reduce flow when you need it - just before pump off mode. Your fastest test is to crank the shut off pressure up to 60 or 80 and see if THAT flow reduction reduces hammer. Sounds like your pipes are good for 300+ PSI if they survive such water hammer. If that works, you might just add a pressure regulator after the tank.

Just to clarify, you only have hammer at shut off, correct?

ballvalve

OK, I think I have seen a dole valve now! It had a set flow rate and was used to maintain pump output at or below the yield of the well............. used one to deal with a low yield well. There was one place in the water line under the house where a hanger dug into the pvc pretty deep but I could easily fix that if I could deal with the hammer problem. I'm thinking I'd like to try the CSV ................... been wanting to try one anyhow.

So, the dole valve does the same thing as a throttling valve only without the turbulence caused by a partially closed service valve right? Plus the dole valve couldn't be tampered with like a valve...

Oh yeah, the hammer is at pump shut off.

Valveman, where do I get a CSV? I believe that the pump is producing 30GPM and all the related plumbing is 1-1/4" pvc schedule 40. Give me your recommendation on what I need.

Thanks,
TS

The CSV will only be allowing 1 GPM into the pressure tank at the time the pump shuts off. This means your check valve will only be open the width of a piece of paper, which eliminates water hammer on shut off. However, if you check valve is sticking open and won't close until the flow reverses, nothing will solve the problem except a new check valve.

CSV's are matched to the pump. Do you have a model number, horse power, and static water level?