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Chemical & Process Technology

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Sunday, May 27, 2007


Someone raised a question :



Non-Return Valve (NRV) is provided on centrifugal pump discharge to avoid pump damage due to backflow. In some special case, designer provide a manual block valve across the NRV. Why ? Isn't it defeat the purpose of NRV ?







Infact there are several reasons behind this application...


Art Montemayor :
" 1. Prime the pump with the discharge fluid that is on the downstream side of the check valve

2. Drain the discharge fluid that is on the downstream side of the check valve."




JoeWong :
"If the pump is started-up automatically whenever the duty pump failed, then the standby pump discharge isolation valve shall always open. The bypass gate shall always open to allow small amount of hot fluid from discharge manifold back to suction manifold. Allowing hot fluid passing the standby pump will always keep the pump hot. Whenever the standby pump kick in, it is ready to receive hot fluid avoid pump crack due to uneven thermal expansion. Sometime designer drill a hole at check valve to perform similar function..."


So got it ?


WebWorm
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posted by Webworm, 6:07 AM

5 Comments:

Anonymous zaki said...

Maybe you can further explain/compare non return valve and manual block valve. I'm not aware of the manual block valve....

If you have a photo / illustration, that's even better...

Thanks for the info mate...

May 27, 2007 at 9:33 AM  
Blogger Webworm said...

Manual block valve is just common name for valve use for isolation purpose...There are several types of block valve such as butterfly, ball, gate, etc

Non-Return Valve (also call check valve) use to avoid backflow...

check out photo from this links...
http://www.alibaba.com/showroom/Check_Valve.html

May 28, 2007 at 3:45 AM  
Anonymous zaki said...

O ok....it's just a term....ok i understand ...tq

May 28, 2007 at 10:12 AM  
Blogger Qalander(Chem) said...

Dear All,
We knew this as 'Warm-up Valve'
There may be problem if too-much flow in reverse direction,thus careful sizing is very important.
Additionally while handling highly viscous fluids through multi-stage centrifugal pumps driven by electric prime movers;such a valve helps in (soft start)i.e. lower initial starting currant.
Best Regards
Qalander(Chem)

April 23, 2008 at 12:44 AM  
Blogger Webworm said...

@Qalander(Chem,

Interesting points...

April 23, 2008 at 12:29 PM  

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