Check Valves

[ccc123]

I have asystem with two pumping stations.The first station is pumping to the second with about 50bar. Due to power failure the expected surge pressure on the first pumping station is about 70 bar.The system is protected against surge by using surge tanks, at the discharge line of each booster pump in the station their is one check valve,But their are no check valve installed at the main pipeline between both stations, My question : is it recommended to install check valves at the line between the two stations to prevent back pressure or it's enough to depend on the surge tanks ? where it is recommended for installation ?
If the CV will be installed at theinlet line of the surge tank this will prevent the surge tank from working, so no need for surge tank ??

 

[Ashereng]

Are you pigging the line? If yes, a check will get in the way of the pig - which may be the reason why you don't see a check in the line between the stations?

"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
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[stanier]

You will need to consider the dynamic performance of any check valves in the system as they have a direct impact of the transient surge pressures. Data from the valve manufacturer giving reverse velocity versus fluid deceleration needs to be input into your analysis software. You cannot guess what is going to occur.

The inclusion of a fast closing check valve at an intermediate point in a pipeline can possibly halve the surge pressure but it does depend on the pipeline grading and HGL.

Noreva check valves are rapid closing valves that rpevent surges. But again you need to model the performance against the valve characteristiics.

You may be able to do away with the surge tanks. One way Surge tanks only protect for negative pressure and the resultant recombining of separated columns. In practice the positive surge wave will pas the inlet to the surge tank before the momentum of fluid can do anything to mitigate the pressure transient.

Sugggested reading Fluid Transients in Pipeline Systems ARD Thorley. This reference covers the work by Thorley with Delft laboratories in the Netherlands.

"All models are wrong, some are useful" George Box.

Geoffrey D Stone FIMechE C.Eng;FIEust CP Eng

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

 

[ccc123]

Thanks Stanier,

The system is already constructed,after two weeks we will start the run it. The design was done without assuming the existance of any check valve at the main line and we installed the surge tanks.from my experience you can do surge analyses but you can not expect every thing will happen when you run!

In your last paragraph "In practice the positive surge wave will pas the inlet to the surge tank before the momentum of fluid can do anything to mitigate the pressure transient" so mainly installing the surge tanks will reduce the duration of pressure surges by damping it and reducing magnitude gradually, if we can reduce the magnitude of pressure by installing check valve at intermediate point in the pipeline why we couldn't install it ? my concern exactly about the disadvantage of installing the check valve or what is the possible bad results that we may have after installing it ?
Check valve has a direct impact of the transient surge pressures but for sure it will reduce the surge ! can you explain it to me ?

 

[stanier]

Hi CCC123,

The check valve prevents the return pressure wave returning form the end of the pipeline and combining with other pressure transient pressures at the pump. The use of an intermediate check valve is a common method of solving high pressure transients that occur at the pump and compromise the mechanical seals or casing pressure. I am talking here of systems with a relatively high static pressure.

This is particularly necessary when the pump is constructed of cast iron and the design pressure is less than the pipeline and valves.

Refer to

http://www.pipingdesign.com

and check out two papers I have posted there on surge. Also contact Noreva and ask for details on check valve performance. Mention my name if it helps.

Geoffrey D Stone FIMechE C.Eng;FIEust CP Eng

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