Deep well - PVC crack between pump and torque arrestor

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Midriller

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In this (crappy) drawing of this guy's well. #1 static is based off the fact he said he didn't want to use galv. under water so almost all the PVC is in static. This seems less likely to me so static #2 is 200' above the pump at the same level or within 20' as check #12. In what scenario, whitout multiple failures of check valves can I see water hammer?
 

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Midriller

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Also double door/silent checks will still chatter at low flow, not commonly used in residential stuff, but when the flow drops they chatter, Have you ever seen an old tractor with the pivoting exhaust cover that at low idle tings as it closes every few seconds, this has nothing to do with cylinder fire and everything to do with overcoming the fact that their is not enough exhaust velocity (flow) to keep it open and the backpressure has to build then release and repeat. This is the same physics that act on a spring, swing, ball,o double door check valves and when you choke a pump capable of 20 gpm to 1 gpm (VSD or CSV) your check valves will chatter.
 

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In this (crappy) drawing of this guy's well. #1 static is based off the fact he said he didn't want to use galv. under water so almost all the PVC is in static. This seems less likely to me so static #2 is 200' above the pump at the same level or within 20' as check #12. In what scenario, without multiple failures of check valves can I see water hammer?

Check valves don't have to fail to cause water hammer. Negative pressure happens when a lower check closes just a fraction of a second slower than an upper check, or leaks back just a few drops. With a 40/60 switch and the upper check at 147', there is always between 103 to 123 PSI holding that check at 147' closed. If the upper check leaks back, it is supplied by water from the pressure tank, so there is always at least 103 PSI holding that check closed. Any check below that and above the static will cause a negative pressure when closing slow or leaking a few drops.

When there is 103 PSI above the upper check and a negative or even just static head below, water hammer will happen on pump start. The negative or static head is what the pump sees when it comes on. This lets the pump get to full flow rate in a tiny fraction of a second. When the full flow rate of the pump hits that check with 103 PSI holding it closed, it is like a freight train hitting a huge boulder on the tracks after it has had time to reach full speed. The difference is it may take several miles for a freight train to get to full speed, while a pump gets to full flow in a fraction of a second. With multiple check valves as in your drawing, a pressure wave crashes into each check valve on the way up. Every time the flow hits a closed check valve is sends a transient wave back down. And since the check valves below are already open, the transient goes all the way to the motor thrust bearing.
 

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Also double door/silent checks will still chatter at low flow, not commonly used in residential stuff, but when the flow drops they chatter, Have you ever seen an old tractor with the pivoting exhaust cover that at low idle tings as it closes every few seconds, this has nothing to do with cylinder fire and everything to do with overcoming the fact that their is not enough exhaust velocity (flow) to keep it open and the backpressure has to build then release and repeat. This is the same physics that act on a spring, swing, ball,o double door check valves and when you choke a pump capable of 20 gpm to 1 gpm (VSD or CSV) your check valves will chatter.

Water is not compressible, air and exhaust gases are. If you are flowing a smooth 1 GPM of water, the check valve will always be open enough to allow 1 GPM to pass. With a loose stem or poppet it can rattle side to side, but it must be open enough to allow the small flow rate. Even rattling is caused by the turbulence or pulsing from vane passes in the impeller. With six vanes in an impeller and the pump spinning at 2000 RPM, there is a vane pass frequency of 12,000 times per minute. This is much more noticeable, causes more turbulence, and bounces check valves more than a vane pass frequency of 20,700 times per minute as when the pump is running at full speed.
 

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Your logic is flawed, This may be true in a system improperly set up with a check at the bottom and one at the top. In my set up if lets say Check valve #4 closes slowly (#2 is carrying the pressure from tank) How does that have anything to do with water hammer on start up. IT DOESN'T!!!!!! How are you creating a negative pressure on pipe section #3 if pipe section #5, #7, #9, #11 has a positive pressure below. The answer is you cannot. Even if you theory was correct for a split second. the pressure from below would equalize from below and create a slightly positive or atmospheric pressure at least in pipe section# 3. Which would eliminate any water hammer on start up as well as reducing wear on your check valves and providing redundancy in a 1200' string. If Check valve #12, #14, or #15 were to leak back slowly (with Static Level #2). They are either submerged or close enough that making negative pressure is impossible. This is how every competent well professional I have ever met, sets up a deep well string.

Again I don't follow your logic with a check valve. If a VFD is chattering a check valve at 60 bpm and a CSV is chattering it at 20 bpm, Who cares. Its still chattering it. Are you happy to be slightly better than the VFD. Also variable flow check valves solve the problem because they are essentially 2 check valves in one, a small diameter check valve for low flow and a large diameter for large flow with progressive spring rates to ensure the small opens first. This is also very helpful as the check valve progressively closes on shut down. With that being said almost all VFD/CSV setups are slow ramp down anyway.
 

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Atmospheric pressure is still lower than the pressure above the check valve(s). Letting a pump start against any pressure lower than the pressure above the bottom check valve, is like letting the train locomotive get up to full speed before hitting a boulder on the tracks. Kind of like firing a rifle with a bullet stuck half way down the barrel. It is not good to have an obstruction half way up the pipe.

The large check valve/small check valve in one thing is not new. Cla-Val has been making check valves and all kinds of valves that way for generations. Anything that solves the problems with VFD's and helps people get use to constant pressure systems instead of thinking their water comes from a tank is a good idea as far as I am concerned. The next step in their evolution is figuring out how to get constant pressure without the complications of VFD. :)

What makes me "happy" is helping people solve their pump system problems. I could be selling expensive and short lived VFD's instead of inexpensive and long lived valves. I recommend what I think best for each application, and sometimes that even means a VFD.

I just recommended a VFD to someone in Hawaii. They have a 75HP set 900' deep, static at 675', filling a huge above ground storage tank. There is only one check valve at the bottom, and this is an instance where multiple check valves would help. Filling the huge storage tank is basically open flow into the tank. The line goes up and over for an air gap, a probe system turns the pump on and off, and there are no valves of any kind, other that the check valve on the pump. Starting at 250 GPM is no problem as the line into the tank is unobstructed. It would be easier for the pump to start against some restriction, but there is no water hammer on start up as there are no check valves for the flow to crash into. The problem is water hammer on pump stop. With the check valve wide open at 250 GPM when the pump stops, the water reverses a couple inches as the check valve slams. This is the kind of water hammer and check valve failure that is helped with multiple check valves in the line. But only when pumping open flow on the ground or into a storage tank at open flow will multiple check valves not cause water hammer on pump start.

When pumping into a closed system and using a CSV, the pumps flow is reduced from 250 GPM to 5 GPM filling the pressure tank before the pump is shut off. At 5 GPM the check valve down on the pump is only open the thickness of a piece of paper, so there is no slam or water hammer when the pump shuts off. While using multiple check valves can reduce water hammer on pump stop when pumping open flow, they cause tremendous water hammer when starting a pump into a closed system.

The system in Hawaii had no place above ground to install a CSV and convert it into a closed system, They also did not want to barge a rig over there to pull and set and add additional check valves. So I recommended a VFD with a ramp down feature. The VFD was going to be a very expensive option, but should solve the water hammer on pump stop. In an open system, ramping the motor speed down until the pump is only producing 5-10 GPM before shutting the pump off, has basically the same effect as a CSV closing down to 5 GPM in a closed type system.

I think the idea of multiple check valves still hangs on from the old hydro-pneumatic tank days. Pumping into a hydro tank is basically the same as an atmospheric storage tank as there is no obstruction. The water only hits a cushion of air in the tank. With the bleeder system there is even a cushion of air between the upper check and bleeder. It is different in a closed system with a bladder tank teed off to the side. There is no cushion of air for the water to hit when the pump starts.
 
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