Hi Omid
I am a little confused by your description of a one way surge tank. The
ones I am used to have a check valve which lets water into the pipeline
when the pressure drops below the surge tank static head, as described
in Karassik's Pump Handbook. They are normally located below the
hydraulic grade line to stop them running out of water when the system
is off. The check valve prevents the tank from overflowing during normal
operation. Recharge is normally by a branch off the main line and a
float valve. In many circumstances I have found them specified where
reliable vacuum breakers (or some times a standpipe) would work at far
lower cost. Water hammer software allows for the cushioning effect of
the air, although the exact details are seldom forthcoming from the
software vendors.
The main problems with vacuum breakers are reliability assurance (double
breakers sometimes used), avoiding hammer in the empty pipes on startup
(prime lines under throttled conditions) and what to do with the trapped
air in the system (two stage air valves or separator at discharge if the
hydraulic gradient permits).
From what you describe it sounds like your check valve lets water into
the tank but not out. Obviously I am missing something here, as such a
system would not help on a downsurge.
Could you clarify your arrangement please?
Cheers
Steve
-----Original Message-----
From: Omid Hamlehdar [mailto:omid_7_ae@yahoo.com]
Sent: Tuesday, December 07, 2004 6:06 PM
To: PipingDesign@yahoogroups.com
Subject: RE: [PipingDesign] Surge Tank
Dear Erik
Thank you for your reply,
As I have mentioned it is a one way surge tank and so, I have modeled a swing check valve to prevent tank from draining back when pump is off.
As you mentioned Surge tank prevents a fluid column separation and rejoining but I have modeled a one way surge tank which is different as you know.
My concern is about this column separation, I suppose to locate an air valve (twin air valve from Erhard) to allow this air will be released, but I still want to know your opinion, do you think it is ok if air will enter to system after water has been finished in one way surge tank? Actually I have found that I need a huge amount of 800 cu meter to prevent air entering to system but it is impractical, I have decided to allow air enter to system after water has been finished in a smaller one way surge tank and locate an air valve to allow air released in re-starting.
Best regards
Omid
> What are the boundery conditions ?
> Is there a receiver at a height over 33ft above the
> level of the tank from
> which the water is drawn?
> Is there a valve a the end of the pipeline who
> closes to prevent the tank
> from draining back when the pump is off?
>
> A surge tank prevents a fluid column separation and rejoining.
>
> When air enters the pipe and the pump is restarted,
> the column of water will
> be accelerated into a partial empty pipe. Given a
> long anough void, the
> column of water can accelerate to its terminal
> velocity of perhaps 5 to 10
> fps before striking the valve face.
> Upon collision with the valve, the kinetic energy of
> motion is converted
> into potential energy by compressing the liquid.
>
> There should always be water in the surgetank.
>
>
>
>
>
> _____
>
> Van: Omid Hamlehdar [mailto:omid_7_ae@yahoo.com]
> Verzonden: maandag 6 december 2004 11:51
> Aan: PipingDesign@yahoogroups.com
> Onderwerp: [PipingDesign] Surge Tank
>
>
> Hi everybody
>
> I have a question and will be pleasure to have your
> opinion.
>
> After analysis a pipe line for water transfer
> purpose,
> I found that I have extreme down surge, to suppress
> this surge I assumed a one way surge tank, my
> question:
>
> 1. Is it ok if air will enter in pipe line
> after water
> has finished in one way surge tank?
> 2. In terms of restarting (priming) the line,
> if air
> has entered to system, is there any consideration
> required regarding probable impact regarding column separation in
> line?
>
> Your contribution is highly appreciated
>
> Omid
>
>
>
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