Water hammer

Recently I've noticed that when I shut the pump off, I hear a significant bang in the squipment, near the heater. I believe this to be "Water hammer", which is the force of the water banging against the pipes after suddenly being stopped by the pump shutting off. 2" PVC full of fast-moving water doesn't stop on a dime, so when the pump shuts off I believe a big water hammer shocks the system.

This can't be good, can it? As an aside, when the PB was here, we were talking about the heater bypass valve. I had it fully closed, so that 100% of water goes through the heater. He said that was "too much" and that I only needed to divert 40-50% of the water into the heater, with the rest "bypassing" it and going back to the pool/spa unheated. He said the heater couldn't "handle that volume", which is BS since the heater has its own internal bypass that can deal with up to 125gpm, and my pump only pumps around 90gpm (I did the calculations). I reset the bypass back to fully open after he left (he also had a lot of other bogus advice, which is why I did not believe any of what he said). But, when the valve IS set to 50% bypass, I don't hear the water hammer when the pump shuts off. Should I be concerned?

Don't know anything about the heater bypasses so this is just a thought. When the pump is running you have water being 'pushed' thru the heater. When the pump is killed, you now have the mass of water in the pipe after the pump trying to keep moving and now the situation has changed to one of 'pulling' water thru the heater, possibly a valve in the heater or something else in the heater is slamming shut?
Al

First, that is total bull excrement about bypassing the heater. The more water you run though it the more heat you will extract although the temperature of the exit water will not be as high, the total heat absorption will be the same or higher - so don't worry about that.

If you are having water hammer what you could do is cut into the line and add a Tee in the horizontal position with the branch facing up. To that add about 12-18" of pipe and cap it. This will work to absorb the force and eliminate the hammer, this is done in piping systems all the time.

Please, cleancloths, no need for profanity if you disagree. We try to keep things as civil as possible on this board, which is different than many parts of the web.

Thanks,

EricF

I think Poconos is on the right track. I would believe "water hammer" to be caused by a blockage of the flow (like shutting off a faucet). You don't have that when the pump quits....just a loss of pressure.

I wonder if that internal bypass in the heater is coming in to play somehow?

As an aside, I would question the PB further on the external bypass. It seems it could at least be used to keep the sytem operating if you ever had to remove the heater....it may have another function as well.

The internal bypass in your heater is probably setup to make sure youre always getting about 50 GPM through the heat exchanger and sending the rest past. Auto-Pilot's bypass system for their SWG works in a similar fashion. Also, This bypass probably has some type of check valve, and you probably have another one between the heater and your chlorinator, and I'm guessing that you are hearing these valves when they slam shut. If you take a spare Jandy Check valve and manually open it and then just let go it pops closed with a very audible thud.

Brad
Waterworks Pools

cleancloths, thanks for the excellent suggestion for a relief tube allowing the water to use air as a cushion during its deceleration. I may end up doing that.

Waterworks, also an excellent observation. I actually don't have all that many check valves in my system, I believe there are only two: one on the spa return, and one on the solar system. I'm going to do some more research into exactly where the hammer sound is coming from. It doesn't happen *all* the time, probably 80% of the time. But it's loud and so I am concerned that one day it will POP a PVC elbow or other welded joint, or the pipe itself (or worse, blow something up inside a piece of equipment!).