Is this really water hammer?

[Seeper]

When my well pump turns on, there is almost no sound from the water system pipes. If you're not paying attention you can't hear it. However when the pump stops, there is a very loud THUMP which can be heard from almost anywhere on the first floor of the house. There is no such thump when you turn on a faucet, shower, or even a fast-moving valve like on the dishwasher or washing machine. It only happens when the pump turns off. The previous homeowner had the well and pump installed in 2016 after having to give up his previous "gentleman's agreement" water supply from a neighboring property's well. So the well and pump are pretty fresh but the pressure tank has been in service a while. The previous owner mentioned the thumping sound when we bought the property 2 years ago, but I don't know if it was going on from Day 1 of the installation. I was new to well systems then and didn't know to ask further.

There are no surge arrestors or expansion tanks in the system. Only the pressure tank provides any buffer to pressure spikes.

Oddly, though, the local pressure gauge needle does NOT spike when the pump stops and I hear that thump. It stops cleanly upon pump shutdown. I have watched some YouTube vids of pressure gauge needle action on systems suffering from water hammer and my gauge doesn't act like that at all. Couldn't ask for a cleaner, more stable pressure response at shutdown.

Observations:

- Per what I see on the gauge during a cycle, the pressure switch is set for a on/off cycle of 43 psi to 67 psi. This is after a local well guy tweaked the switch trying to fix the problem. This switch was replaced 1 year ago after the original one's contacts got worn out after 13 years service.

- With the system depressurized and drained, the WellXTrol WX-202 pressure tank's air pressure is 38 psi. The tank has been in service 13 years but shows no apparent signs of failure/waterlogging. As best as I can recall, it takes over 1 minute upon pump start at 43 psi to reach 67 psi (may be longer, it's been a while) and once the pump stops at 67 psi, the system stays pressurized there with no bleed down. Tapping on the sides shows water where it should be and air where it should be. The tank seems OK.

- I went along the cold water lines in the crawlspace and added some pipe supports. However there is a vertical pipe run up to a 2nd floor bathroom where I can't access the lines and I think the pipe banging may be in there.

- The well pump has an internal check valve. Critically, I do not know if there are more check valves in the drop pipe. I don't think I see another check valve near the pressure tank & switch but I'll have to take another look.

- At the wellhead before the pipe goes underground to the house, there is a hose bib connection. I'd love to attach a pressure transducer there and get the pressure response on a graph on a computer, but I haven't found an affordable hardware option for that.

So is this really water hammer? Or just some poorly supported cold water lines? I have read that water hammer can happen so fast you never see it on a gauge, but could the needle really stay so stable at pump shutdown if there was hammer going on? Since there's no THUMP when the pump starts, that rules out a check valve failure, right?

Well system overview:

- 625' deep into bedrock
- pump set at 400'
- static water at 140'
- 30gpm yield (wow!)
- pump is 1.5hp Schaefer Series V 2-wire, 10gpm 230v, model 10SV15S4-2W230. Pump installed in 2016.
- 1" PVC drop pipe
- from the well head, it's about a 50' horizontal run to the pressure tank, with only a few tees & elbows
- duty cycle on the system is light since only 2 people live here

Thanks for reading, I'm curious what the old hands here think.

I'm also curious as to why such a powerful pump is set so deep on such a high capacity well, but that is a topic for another thread.

 

[Valveman]

Your pressure tank is a huge expansion tank and surge arrestor. Transient pressure waves that cause water hammer travel at +- 5000 feet per second. That is several times faster than a speeding bullet, so they can't be caught with an expansion tank or surge arrestor. You have to prevent water hammer from happening, not try to catch the surge with a tank.

The same cycling on and off too much that burned the points in your pressure switch, also wore out your check valve(s) from all the slamming. Your 202 tank only holds 5 gallons of water, which isn't half large enough for a 10 GPM pump. An 86 gallon tank would have been a better size tank, and would have put off the wear on the system by a factor of 4. An 86 gallon tank would have cut the cycling by 75%. However, your little tank is actually larger than you need when using a CSV1A. The Cycle Stop Valve and tank you have would cut the cycling by even more than the 86 gallon tank. Plus the CSV completely eliminates water hammer on pump start or stop. You would also like the constant 60 PSI in the shower, compared to the repetitive cycling between 43 and 67 that you are experiencing now.

The fact that you have already worn out a pressure switch and check valve(s) means your tank diaphragm and pump also have a lot of wear on them. You might want to consider replacing the tank while you are fixing things, as it is probably on its last leg. You could replace the tank and add a CSV with a PK1A kit and a 10 gallon size tank. It will work much better than what you have.

Adding the CSV will most likely stop the water hammer on pump stop. But it is possible that your check valve(s) are so worn out they will stick in the open position anyway. In that case the water will have to reverse direction before the check valve(s) will close, which is what is causing the water hammer now. If adding the CSV doesn't keep the check valve(s) from sticking open, the check valve(s) will have to be replaced to solve the hammer problem. But changing out the check valve(s) without adding a CSV means it will just happen again.

 

[Sponsor]

 

[Seeper]

Cary thank you for your info, I was hoping you'd reply. You may recognize the following narrative based on a phone conversation you had this week with a plumber here.

Upon further exploration I found out some more about this system.

I looked up the WellXTrol sizing guidelines and as Cary said, my pressure tank is woefully undersized. Gotta fix that.

But I found another thing: the 60' PVC pipe run from the well head to the pressure tank is 3/4", not 1". The well's drop pipe is 1" PVC. So why the weird step-down in piping and undersized pressure tank, despite the well being a 30gpm gusher with a 10 gpm pump? Based on info from the previous homeowner I think I've figured it out.

2005: previous owner (let's call him Bob) builds this small house and lives alone. Neighbor on the next parcel has a low yield well that's not in use, so Bob has a verbal gentleman's agreement to use the well on this parcel. This is great for Bob because there's no municipal water out here and wells are expensive. Everything goes fine for years.

2015: owner of the next parcel dies. Bob never got the well agreement in writing. The parcel's new owner tells Bob to stop using the well. Bob has to have his own well drilled at great expense. The driller's work order (of which I have a copy) is to drill the well, place the pump, and "connect to existing home plumbing system", which he does. Bob is not a technically inclined guy in any way, so as he described to me in person, "the banging sound has always been there, I didn't worry about it".

I think what happened is that Bob got a big new honkin' well, but never had the house's downstream plumbing system re-sized to handle it. So now I have a powerful well shoving water into a 3/4" line and a real small pressure tank.

Do you guys think the 3/4" line is a factor here? I.e. is it part of the banging problem, or is it simply a restriction that isn't a big deal either way?

My plan to move forward:

1) Put in more pressure tank capacity, which may require 2 tanks side-by-side due to vertical space restrictions.
2) Replace the 3/4" ditch line with 1".
3) Put a CSV in the system to make it even better.

I think step 1 needs doing to take out some of the impact that's hurting the system. Even with a CSV I'd like a little more pressure tank capacity for intermittent uses.

I am unsure if step 2 is really needed.

I am convinced of the CSV's value and will eventually do step 3.

What do you guys think? Especially about the 3/4" line from the well.

 

[LLigetfa]

My plan to move forward:

1) Put in more pressure tank capacity, which may require 2 tanks side-by-side due to vertical space restrictions.
2) Replace the 3/4" ditch line with 1".
3) Put a CSV in the system to make it even better.

I don't agree with the numbering if'n it is a priority list.

#1 should be the CSV. It is the easiest and least expensive improvement and might negate the other two. Of course we cannot know your water use pattern as to whether the 3/4" line will be a problem. Simply setting a higher pressure might compensate for it.

Folks often make the assumption that having more tank capacity will work in their favor. The flawed thinking is that the tanks will always be full to start with. Murphy's Law is that they will be a few cups short of empty.

 

[Seeper]

I don't agree with the numbering if'n it is a priority list.

#1 should be the CSV. It is the easiest and least expensive improvement and might negate the other two. Of course we cannot know your water use pattern as to whether the 3/4" line will be a problem. Simply setting a higher pressure might compensate for it.

Thank you for that and I agree with you. My problem is that around here, nobody has any history with CSVs while plenty can put in a pressure tank properly. Because a CSV has to be the first thing in line to the house, and the arrangement at my wellhead, the one guy I've talked to says the CSV would have to be buried in some sort of box near the wellhead. There is a hose bib right there for watering the garden, so that keeps me from just putting in the CSV near the pressure tank.

So it's more involved that just cutting the line and dropping in the CSV. I'm a very technical person (industrial control systems) but I'm not a plumber, don't know best plumbing practices, and I would like a licensed plumber to do the work.

Right now I just want to move quickly to prevent a cracked pipe. So I thought I'd get the larger pressure tank in, then slog through what it will take to get a guy to install the CSV. Cary has said that a surprisingly small tank works well with a CSV, but a moderately larger one will reduce the number of pump starts due to intermittent water use.

I am interested in your comment about water use pattern and the 3/4" line. It's just my wife and I in the house, so the usage is more moderate than that of a bigger family. Are you saying that the 3/4" line limits throughput, but is otherwise OK as long as we can live with that throughput? I want to make sure I'm understanding you.

 

[LLigetfa]

My knowledge of American flags is poor and you put "Local" for you location so I have no clue if your ground is frozen WRT to the hose bib and watering the garden. Installing the CSV at the tank is of course the easiest but the hose bib complicates it. There is a model of CSV that can be installed in the well.

The friction loss on 3/4" pipe depends on the GPM and the pressure. Assuming the CSV is at the tank, the pressure on the 3/4" line would be much higher. If you need to keep a hose bib near the well, then trenching in a new larger line makes sense and the old 3/4" line could be repurposed to supply the hose bib.

 

[Valveman]

I agree with LL that adding the CSV may negate the need for anything else. However, since you have to put the CSV prior to the hydrant used for irrigation, you could also replace the 3/4 line at the same time. If that is a SC flag, your water lines should not be very deep. If the 3/4 line is 24" deep or less, adding a valve box is not hard.

Your first and easiest option would be to dig up the line prior to the hydrant. Cut the line and splice it back together with a CSV1A. Place a 24" valve box over the CSV and back fill around it. Save your money on doing anything else until you see if that stops the water hammer thump on pump stop. If you still have the thump, you will need to spend your money pulling the pump and replacing the check valve attached to the pump.

Thump or not, by then you will see how the CSV works and understand that adding any additional tank is unnecessary. As long as the 202 tank is still good, it is 2 to 4 times larger than you need with the CSV. A 4.5 gallon or 10 gallon tank is all that is needed with the CSV system. Even though the CSV will work fine with any size tank, larger tanks negate the benefit of constant pressure from the CSV. With a large tank you are experiencing low pressure while waiting on the tank to drain all the way to 40 PSI and the pump to start. With a smaller tank, that happens much quicker, and you get the strong constant 50 PSI that keeps you from even needing soap in the shower.

 

[VAWellDriller]

I think your thump is check valve or pipe support related.....202 is a pretty standard installation around here with a 10 gpm pump (even though it's undersized). You said cycle time was longer than 1 minute which it shouldn't be with that pump....should be more like 30 seconds. You also mentioned sort of checking for other check valves but not being sure; you need to be sure, check all the plumbing thoroughly around the tank especially, and remove any other check valves you see. I also don't think the 3/4 line to the house is a problem...especially since it's only 50' run; I've seen lots of homes with 3/4" copper lines in the ground, no problem on getting enough flow for normal use. Seems to me like instead of digging anything up, you could pop get your pump man to install a 60 psi CSV125 in the well and go with it.....while he is there, it would be help to look for and remove additional check valves in the drop pipe and check the one on the pump. A 2nd check valve, (high quality brass or stainless) installed within a few feet of the pump is a good idea. I would also look around and make sure the plumbing that was there connecting the house to the neighbor is fully disconnected and or capped off.

 

[Seeper]

Great info guys, I really appreciate it.

To fill in some gaps:

- I'm in upstate SC so it's not super cold. I'm told the standard depth for buried plumbing here is 18".

- I looked again and there are no check valves around the pressure tank, which is in a relatively roomy crawlspace. However there is a steel bodied check valve within a foot of where the line comes out of the top of the well head. I can hear it click when the pump stops. I can't make out any markings but it looks like 1", which gets necked down to 3/4" CPVC before the hose bib. Then the pipe goes into the ground.

- I was wrong about the pump's cycle time. I timed it with a stopwatch and its right at 45 seconds, much more in line with VAWellDriller's feedback. This is when a cycle occurs without ongoing usage at a fixture.

I am very grateful for the feedback on the 3/4" line. Sounds like we don't have to jump on that any time soon. Whew...

After some more testing, I have some interesting results that I'll compose here in a bit.

 

[Seeper]

Yesterday evening I set up a test. I wanted to see if the thump happened when the pump stopped while there was ongoing water use at a fixture. I expected there would be no thump since any pressure wave would have a relief path through the open fixture. Why the pressure tank was not serving in that role is beyond me.

I can sit in the door of the crawlspace and observe the pressure tank and gauge. I ran a hose to the nearby bib and put a ball valve at the end, then aimed it at the yard. This let me control water usage while monitoring the gauge, and listening for the thump. There is no mistaking the sound.

I opened the ball valve and when the pressure dropped to the cut-in, the pump ran. I left the valve open and as expected, when the pump stopped there was no thump. When the thump happens you can also feel it in the line going to the pressure tank. No thump.

OK fine. Then, I ran another cycle, but this time kept the ball valve closed once the pump started. The cut-out pressure was reached, the pump stopped... and there was no thump. At all. What the...? For the whole time we've lived here the thump has always happened at cut-out. It happened over and again last week when I had a local plumber here to help with diagnosis. Every time, as long as there was no ongoing flow from a fixture.

So I ran more similar trials, spaced out over time. Never a thump, even with no fixtures open. I went inside and doublechecked that no water was in use. None was. Today I carefully monitored water usage, witnessed several normal pump cycles, and there was never a thump. Just a clean, quiet pump cutout. We cooked, ran laundry, washed up, and filled water jugs. Never a thump.

There's one more weird thing: occasionally when a fixture is opened there's a quick double pulse of pressure, as if the tank's pressure switch contactor is chattering, then the flow is even. It doesn't happen every time, or even half the time. It is mild, not a harsh hammer at all. But it is different than than the past history.

No equipment has been adjusted or changed. I cannot explain it. This thump had been ongoing upon pump stop for the 1.5 years since we've lived here. Like clockwork.

SWAGs:

- A check valve had a small bit of debris in it preventing proper operation, and that debris finally got flushed out? Dunno.

- For some reason the pressure tank was operating intermittently? Dunno.

I don't get it. Ideas?

 

[LLigetfa]

So I ran more similar trials, spaced out over time. Never a thump, even with no fixtures open.

Did you have the garden hose still attached and pressured up with the ball valve on the end closed? It is possible that due to its elastic nature, the garden hose acts as a hammer stop.

Why the pressure tank does not act as a hammer stop may due to how it is plumbed.

 

[Seeper]

Did you have the garden hose still attached and pressured up with the ball valve on the end closed? It is possible that due to its elastic nature, the garden hose acts as a hammer stop.

Why the pressure tank does not act as a hammer stop may due to how it is plumbed.

Good point on the hose. Yes, during the tests last night the hose was pressurized. But it was similarly pressurized when the plumber induced the thump with it last week. And during today's wide and varied water use, the hose was turned off at the bib.

Can you expound how how the tank's plumbing can inhibit it's impulse absorbing capability? I thought if the tank was able to be pressurized by the pump and then pressurize the house plumbing, it must be able to absorb some pressure impulse.

 

[LLigetfa]

And during today's wide and varied water use, the hose was turned off at the bib.

That'a what I was asking, so the hose acting as a hammer stop theory is busted.

Depending on the source of the pressure wave, it takes the path of least resistance and might see the Tee to the tank as a high resistance and just fly by.

 

[LLigetfa]

However there is a steel bodied check valve within a foot of where the line comes out of the top of the well head.

As a test, you could remove the innards on that check valve.

 

[Valveman]

As a test, you could remove the innards on that check valve.

Removing the innards from a second and above ground check valve will stop water hammer that happens on pump start. If there is a second check valve above ground, removing the innards might possibly stop the water hammer on pump stop, but maybe not. A check valve or check valves stuck in the wide open position only close after the pump stops and the water reverses, which is what causes the water hammer on pump stop. Removing the innards of the above ground check valve may or may not stop the lower check from sticking in the wide open position. Worth a try, but still think you will need to replace the check valve on the pump at the bottom of the well.

 

[LLigetfa]

Removing the innards of the above ground check valve may or may not stop the lower check from sticking in the wide open position. Worth a try, but still think you will need to replace the check valve on the pump at the bottom of the well.

The check valve in the pump doesn't have a chance to work as designed if there is another check valve downstream. An in the pump check valve might be made to work again if given the chance.

As you say this usually manifests on pump start, not stop but none the less it is worth a try. The OP might find that the above ground check valve innards are already in bad shape while gutting it. Then again, we only know of the two check valves... there could be more of them inline.

 

[Seeper]

Cary, can you give some guidance & a diagram on how to install a CSV1A in the ground near the well head? 18" deep is considered acceptable around here. After the CSV I'll have a yard faucet installed from a new tee in the line, then the line goes to the house.

I thought having the CSV buried would be suboptimal but I can't help it if I'm going to have a local watering source fixture.

 

[Seeper]

I have never noticed any air coming from fixtures during normal life at the house. However, before a long trip I turn off the pump's breaker then flush the toilets and open the faucets for a bit in the house to depressurize them. I want to avoid a break while we're gone. I knew of a guy who had that happen while gone and it ruined their house.

But when we return from a trip and I get the water going again, there is a bit of air discharge upon first using a fixture, then no more. This doesn't sound like check valve failure, does it?

 

[LLigetfa]

A one time discharge of air after having drained the system is normal. A bad check valve in the pump would only produce air if the well water level is below 30 feet and there is a leak in the piping somewhere before the last check valve.

 

[Seeper]

Got it, thank you LLigetfa. That guy I referenced had an upstairs toilet supply line burst while they were on vacation. It flooded the upstairs then flowed downstairs. Over $30,000 in damage and even then the mold was so bad it made the house unlivable.