pipingdesign: Re: Water Hammer and surge

From: <geoff>
Date: Mon Aug 27 2001 - 20:01:00 EDT

In respect of waterhammer analysis I run AFT's Impulse software.(www.aft.com for a demo).

The speed of closure of the check valve is something that one considers to prevent the reverse running of a pump. A rapid closing valve is preferred in respect of the check valve as you are sure what position it is in. With a swing check valve is expected to close you are never sure that it has not hung up. A tilt check is a better option. Red Valve have just put out a flap valve for the water industry that is worth investigating.

A translational type of valve such as those manufactured by Mokveld or Mannesmannn close in less than 0.4 secs. They are not encumbered with counterweights on lever arms. Experience shows that they will ameliorate the peaks of a surge. Whereas a conventional swing check may slam shut when the flow has reversed and the peak pressure will be destructively high.

If a pressure transient greater than the design pressure of the pipeline still occurs then other preventative measures are required. This may include faster acting bypass valves, relief valves, surge tanks, accumulators,etc. The worst case is ususally when the system power is lost, column separation may occur, followed by the columns coming together when flow reverses.

Books by Streeter and Wylie, Boldy, Thorley and Chaudry are worth reading on this complex subject.

Itzhak Shdemati <ishdemati@yahoo.com> wrote: <HR> <html><body> <tt> Hello,

If velocity changed in time T < 2*L/w , sec. dH = w * V / g , ft of fluid

L Length of pipe, ft.
w is the wave velocity. for water in steel pipes w=4680 ft/sec.
V is the velocity difference (V2-V1) ft/sec. g  acceleration of gravity, 32.2 ft/sec^2.

Reference: Handbook of Hydraulics. Ernest F. Brater,
McGraw-Hill.

Itzhak Shdemati

"SARE,  RALPH  H."
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>
>
>       what is the
procedure to predict the pressure rise
> due to rapid
> closure of the check valve?
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