Is this really water hammer?

Discussion in 'Pumps and Tanks Well Forum & Blog. Water is life.' started by Seeper, Dec 31, 2018.

  1. valveman

    valveman Cary Austin Staff Member

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    Mar 15, 2006
    Occupation:
    Pump Controls Technician
    Location:
    Lubbock, Texas
    Just cut the line prior to the tee to the yard hydrant, and plumb in the CSV. It is no harder than adding another tee in the line.

    Leaks while you are away can be a big problem. I am using the Samsung Smarthub with an Aeotec heavy duty smart switch to turn my pumps on and off. I have leak sensors in all the appropriate areas that will shut the pump off if they get wet. It also lets me program on and off times, like the well at my shop comes on at 6:30AM and goes off at 5PM, regular business hours. And I still have the leak sensors in case there is a leak during the day before I notice it. I am working on a way to use this switch for pump protection as well. If you are interested let me know and I will give you links to the components listed above.
     
  2. Seeper

    Seeper New Member

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    Dec 31, 2018
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    Local
    Sorry for the radio silence, I've got some updates. Like a poster here at the site wrote on another thread, I hate it when guys don't follow up with what did or didn't solve their problem.

    I got recommendations from friends on 2 more local well guys. Neither could figure out why the thump happens only upon pump shutdown. I then managed to get the guy who 3 years ago drilled the well & installed the pump out here last week. He confirmed that the only check valves are the one at the surface just past the wellhead, and at the pump itself. I forgot to ask if the deep check was the one integral to the pump, or if there was one installed just above the pump also.

    He wants to
    1) install a second pressure tank (WellXtrol 250) in parallel with the existing WellXtrol 202 to increase the pump cycle times
    2) remove the ground level check valve, and install a new one about 20' down into the well. I don't understand why he thinks this would change things.

    When he was here he removed the ground level check, but was tight on time and needed to order the WX 250 anyway, so he plans to return to finish that work. But in the meantime, I now have a system with a single check (of some sort) down at the pump.

    Here's something interesting: now that the ground level check is gone, the thump is only a fraction as severe as it has been in the past. It's still there upon pump shutdown, but very much reduced in intensity.

    So I ran a test tonight to see if the pump-level check is holding the water column. Recall that I still don't see any of the common indications of check valve failure. I ensured no water use was happening anywhere, then I ran an outside spigot to induce a pump cycle. The pressure switch had been adjusted to stop the pump at 67 psi, so that was the starting pressure. Then I logged the pressure over time for a while:

    time pressure
    (mm:ss) (psi)
    00:00 67
    02:00 65
    05:00 65
    10:00 64
    15:00 64
    20:00 64
    25:00 64
    30:00 64
    35:00 64
    40:00 64
    45:00 64
    50:00 64
    55:00 64
    60:00 64
    90:00 64

    Does this look like the remaining check is holding up OK? I thought perhaps the initial dip in pressure was from some sort of effect from the old pressure tank but I figured you guys would know. If there was an ongoing check failure I'd expect to see more decrease in pressure over time.

    Since a lack of THUMP upon pump startup rules out a failure of the ground-level check, how could it's removal improve things? I just dunno.

    I'm inclined to let the latest guy add the WX250 but not the second check, and see what happens. Also, now that the ground level check is gone, there is ample room to pipe in a CSV above ground, in its place.
     
    Last edited: Jan 27, 2019
  3. Reach4

    Reach4 Well-Known Member

    Joined:
    Sep 25, 2013
    Location:
    IL
    I think so. I have a similar fall off in pressure. I think it is the diaphragm in the pressure tank relaxing.
    https://terrylove.com/forums/index....lbs-of-pressure-at-cut-off.67940/#post-504741
     
  4. valveman

    valveman Cary Austin Staff Member

    Joined:
    Mar 15, 2006
    Occupation:
    Pump Controls Technician
    Location:
    Lubbock, Texas
    Even if the diaphragm in the tank is "relaxing", the water has no place to go. A WX202 holds 5 gallons of water with 20 PSI between on and off. For every 5 PSI it drops you are losing 1.25 gallons of water. 3 PSI loss means about 3/4 of a gallon leaked out somewhere. It could be the lower check since it is still sticking. A larger tank isn't going to help. Another check valve in the well isn't going to help. If he had installed a CSV in place of the check valve that was removed, we would know if the pump needs to be pulled or not. If adding a CSV doesn't stop the water hammer on pump stop, then the pump will need to be pulled and the check valve on the pump replaced. That check valve is sticking in the wide open position, and if adding a CSV doesn't solve the problem, the check valve is beyond hope and needs replacing. Oh and BTW, it was the cycling on and off from not having a CSV that caused the check valve to stick open and apparently also leak when closed.
     
  5. Seeper

    Seeper New Member

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    Today I had a WX-250 installed, running in tandem with the existing WX-202. There is now no thump at all, either upon pump startup or stop. The drawdown and run times are now much better, of course.

    If I decide to have the pump pulled to replace the check valve there, I'll probably swap out the pump at the same time. For now we'll see how the system runs for a while. I will keep a lookout for signs of check valve failure.
     
    Reach4 likes this.
  6. valveman

    valveman Cary Austin Staff Member

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    Pump Controls Technician
    Location:
    Lubbock, Texas
    Can't see that doing anything but reducing the cycles and number of times the check valve closes by 66%. Of course that will help. And maybe the extra time filling the tank gives the sticky check valve time to rattle lose so it doesn't slam when the pump shuts off. I think it is just a coincidence and the problem will return, but only 33% as often. :)
     
  7. Seeper

    Seeper New Member

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    I don't know if the check valve at the pump is the one integral to the pump, or located just above it, or both. If I wind up replacing the pump, should I trust the integral check/foot valve, or should I also have a good quality check valve installed just above the pump? Would that violate the "just one check valve" rule?
     
  8. valveman

    valveman Cary Austin Staff Member

    Joined:
    Mar 15, 2006
    Occupation:
    Pump Controls Technician
    Location:
    Lubbock, Texas
    Adding an additional check valve a few inches above the one that comes on the pump is fine. Some pumps like Grundfos have good integral check valves, some of the others are not very good.
     
  9. Seeper

    Seeper New Member

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    Dec 31, 2018
    Location:
    Local
    I decided to take a look at the pump sizing for my well. I'd like to hear your thoughts on this back-of-an-envelope look.

    - 625' well depth
    - 6" casing
    - pump set at 400'
    - static water at 140'
    - pressure switch set at 40/60psi
    - 30gpm yield
    - 1" PVC drop pipe
    - from the well head, it's about a 60' horizontal run of 3/4" PVC to the pressure tank, with about 5 elbows. This is updated per my recent efforts working on this system.

    Estimating the range of total dynamic head (TDH):

    Pressure switch is set for 40-60psi, so pressure head = (60 * 2.31) = 139'
    minimum head at initial static level = 140'
    approximate friction loss from 1" drop pipe, 3/4" supply line, & fittings = 30' (this is a bit of a SWAG, I haven't been precise on this number)

    Total minimum TDH = 309'

    Sometimes we water the garden & lawn so let's say I draw down 100', so max TDH = 409'

    So, more or less, TDH ranges from 300' to 400'. I would then use a range of 300'-400' on a pump curve, correct?

    I have some suspicions about the existing pump but wanted to make sure I was in the ballpark on TDH first.
     
  10. valveman

    valveman Cary Austin Staff Member

    Joined:
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    Occupation:
    Pump Controls Technician
    Location:
    Lubbock, Texas
    Sounds about right to me. You need a GPM to work with, like 10 GPM at 400' TDH. I think that 60' of 3/4" pipe could be your water hammer problem. At 10-12 GPM that gives a velocity of more than 7 feet per second, which can cause a water hammer when the pump stops.
     
  11. Seeper

    Seeper New Member

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    Dec 31, 2018
    Location:
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    Yeah I'm starting to zero in on how the oversized existing pump may be interacting with the 3/4" PVC supply line. Please tell me if the following is on track.

    The existing pump is a 4" Schaefer Series-V 1.5hp 10gpm unit. Looking at that pump curve in the range of 300'-400' TDH, the pump looks to be operating on the right side of the curve, which would produce high velocities on it's own, then even higher when forced through 3/4" PVC:

    Schaefer 4in V-Series pump curve - 10gpm - 300-400 TDH.jpg

    Since the well's refresh rate is 30gpm, yielding minimal drawdown, I suspect that the effective TDH probably stays closer to 300' than 400'. This yields flows of 11-12gpm.

    Compare to the 1hp 7gpm Series V in the same range of TDH:

    Schaefer 4in V-Series pump curve - 7gpm - 300-400 TDH.jpg

    Recall that I'm interested in switching to this pump in a 3-wire configuration for other reasons (generator compatibility). Since the TDH would still likely be closer to 300', I would get plenty of flow from a pump that's a lot easier to start, and with significantly less velocity in the 3/4" supply line.

    What do you guys think, am I on track here?

    I've still got a CSV in mind, I'm just saving it for last, as the CSV doesn't solve my pump inrush current problem.
     
  12. valveman

    valveman Cary Austin Staff Member

    Joined:
    Mar 15, 2006
    Occupation:
    Pump Controls Technician
    Location:
    Lubbock, Texas
    You are correct the 1HP would have less velocity. It is the velocity at pump stop that is important. If the velocity is 7 feet per second and the check valve is wide open when the pump shuts off, the check valve will slam shut and water hammer will happen. With a CSV the pump is only flowing 1 GPM into the tank when the pump shuts off, and there is almost NO velocity to cause water hammer. Plus the check valve is only open a tiny fraction at 1 GPM, and doesn't slam from wide open and cause water hammer when the pump stops.

    The CSV can help with inrush current if set to the same pressure as the pump starts. Plus the inrush current only happens when the pump starts. With a CSV the pump only starts once per use. It doesn't start over and over and inrush over and over while using water as it does without a CSV.

    Also remember using the longest length of the smallest wire size possible for the size pump you have will make a reduced voltage soft starter and make it easier for a generator to start. This plus starting against an almost closed valve, and not cycling over and over makes it easy on the generator.
     
  13. Reach4

    Reach4 Well-Known Member

    Joined:
    Sep 25, 2013
    Location:
    IL
    View attachment 51613 The curves have all of the info, but the tables are easier to follow for some. I think 7 gpm 1 HP or 10 gpm 1.5 HP would be good at 140 ft and could bring up water if the water level dropped. img_2.png
     
    Last edited: Feb 13, 2019
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