Water Hammer? 3

[NoHandle9]

I have a situation in a water distribution system with a 200 GPM service pump where the first encountered residents are experiencing "hammer" problems in their homes. we have taken pressure readings in the system and static pressure is 105 PSI. when the pump turns on, pressure goes to 140 psi and when it shuts off, pressure drops to 55 and then returns to 105. Is this situation considered water hammer? Is there any recommendations on how to eliminate this problem. The residents are blowing their water meters, not to mention dealing with these pressure flucuations!

 

[Maury]

That's water hammer, caused by a rapid pump shutoff and check valve closing. Normally a water distribution system has a storgage tank or is large enough to absorb the pressure wave. Talk to the pump manufacturer about pressure relieving devices such as a way to stop the check valve from rapidly closing. A soft start/ soft stop system on the pump motor (a short duration variable speed controller) would work.

 

[BigInch]

Classic water hammer case. See my web page "Surge" for more info.

You may be able to install an orifice restriction to alleviate the problem. Its worth a try, if it doesn't also overly restrict fire flows, etc.

Going the Big Inch!

http://virtualpipeline.spaces.msn.com

 

[cvg]

If you are running pressures of 105 psi or greater, your residents should be using pressure reducing valves to protect their water heaters and other plumbing. Recommend maximum pressure of 60 psi for residential services.

 

[BigInch]

Right you are. Sounds like the wrong pump or they are planning for a lot more residents some day and don't have the flows necessary to keep the pump's head from running close to shutoff right now. Its really too much pressure for this system at this time and this should be controlled at the pump.

Quick Options might be,
1.) Install a lower pressure pump,
2.) add a variable speed drive,
3.) install a control valve,
4.) build a storage tank to the right elevation, (hopefully there's a hill nearby) fill it and shut the pump down, then run on gravity pressure from the tank

None of which sound very good. VSD may be your best alternative, but have someone who knows take a hard look at all of these before you go do anything rash.


Going the Big Inch!

http://virtualpipeline.spaces.msn.com

 

[stanier]

NoHandle9,

I very much doubt the peak pressures that you have reported are accurate unless you are using very fast response transducers into a suitable data logger or oscilloscope.

Pressure gauges and conventional transmitters just do not measure a peak pressure wave as it passes the instrument at 1400m/s.

You need to model your system using a sophisticated package like AFT's Impulse. Look at surge on

http://www.pipingdesign.com.

Contact your local consultant, AFT, myself or BigInch if you need the modelling done.

Geoffrey D Stone FIMechE C.Eng;FIEust CP Eng

http://www.waterhammer.bigblog.com.au