Supply line bangs when jet pump kicks in

[Unregistered]

I live in a rural area and my water supply is from a cistern. I have a 3/4 horsepower jet pump. Recently, I had to move the 1" poly supply line in my basement due to renovations. I replaced it with a 1" copper pipe and moved it up from just above the basement floor, to the bottom of the floor joists. Since doing that, every time the jet pump kicks in, I am getting a loud baning noise ( similar to that of an air hammer noise when you turn a tap off ). It only lasts for a second when the pump starts up. I would like to know what I can do to stop this noise. Is there something I can put in the supply line or do to the pump itself ?

[mdshunk]

Uh-huh. You've broken one of the cardinal rules of jet pump plumbing, and you've created an air trap, thus your banging on startup. The corrective action is to rearrange to pipework to avoid the air trap, or move the pump up to the bottom of the joists too. I suspect that your original install was more like the bottom right pic, except you now have a big loop going up and back down to the pump. Jet pump suction side plumbing is somewhat fussy.

[mdshunk]

Also, if the cistern was able to be filled beyond the highest point in the suction side pipework, the problem will also go away. This is not a practical solution regardless of whether you have hauled in water or your gutters fill the cistern.

[DUNBAR PLUMBER]

I am curious to know if he followed your instruction on the matter.

[mdshunk]

He sent me a PM regarding some jerry rigging that he thought would work, which I knew wouldn't. I don't respond to questions by private messages or e-mail. The biggest benefit to answering questions in the open forum is the benefit it will provide others in the future.