Check Valve Proximity to a Centrif Pump Discharge

[JGoldstein]

Can the check valve sit right on the end-suction centrifugal pump discharge flange, or there must be a certain straight pipe run in between? How many Ds? Before or after encreaser? Any specific reference guidelines document? Thank you.

 

[GrampaRoy]

It is possible to mount a check valve directly to a centrifugal pump discharge flange and some skid mounted pump packages do come through that way. Typically, however, there is an increaser mounted on the pump discharge ahead or the check valve. This is usually done to avoid the velocity head losses associated with the "same size" check valve. Swing check, ball check, butterfly and spring disc type check valves all have reduced port sizes and tend to restrict flow considerably.

Be aware also that if you are pumping anything with solids entrained, sewage for example, the bigger the port size, the better.

 

[ccor]

I agree with GrampaRoy. None of my references address this, so two more suggestions. 1) ask the manufacturer after you have selected the pump 2) try posting on the pump engineering forum, those mechanical guys love questions like this.

Good luck.

 

[stanier]

SOme check valve manufacturers specify 6D straight lengths upstream of a check valve.

Geoffrey D Stone FIMechE C.Eng;FIEust CP Eng

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

 

[bimr]

Piping Handbook published by McGraw Hill calls out a minimum requirement of 5 diameters of straight pipe (upstream). The straight pipe is necessary to avoid potential chattering of check valve caused by upstream turbulence. The reference also says that some check valve manufacturers may require up to 10 diameters.

 

[TBP]

Check valves are like control valves - they're typically one size smaller than the correctly sized line. This means that the flow will drive them wide open, and hold them in that position. Otherwise, the disc will flap up down like a flag in the wind, and this is what causes a huge number of checks to wear out far before their time. Crane's Technical Paper No. 410 covers this. I've got the Crane ABZ software that actually has a window pop-up on the screen alerting you to the fact that the size of check valve selected for a given set of flow conditions will not open fully, possibly resulting in a greater pressure drop than the correctly sized (smaller) valve.