Vibration at pump recirculation minimum orifice outlet line

[b1]

We have a recirculating line at pump outlet equipped with a minimum orfice. However, we experienced a vibration at the outlet of the minimum orifice going to the dearator tank (2.7 barg). Pump discharge pressure is at 24 barg. Feed water flow is at 17.5 m3/h.

Is the vibration caused by too much pressure drop? is the replacement of an ARC valve (automatic recirculation valve) would guarantee to elliminate this vibration?

Regards,
B1

 

[checman]

B1:

If the vibration is at the orifice it may help if the ARV is sized correctly. You might also want to try a different type of orifice if you are using a straight edge orifice plate. An orifice nipple that is basically a nipple that is plugged and bored to the correct size takes the pressure drop over a longer area so they would have a larger diameter with a lower exit velocity. Also increasing the piping size that the orifice is in may give better recovery. If the vibration is at the DA it may be that your piping to the DA is too small. The velocity head of the return line could be rattling trays or dividers. A guess would be that 2.5 cm return line would have a velocity head of about 5.28 meters. So it really depends on what is the root cause of the vibration.

 

[pumpkind]

The most probable cause is that the plate material is too thin and vibrates (if you are using a plate between flanges type -if not, please specify what kind of orifice ).

 

[b1]

Thank you checman and Pumpkin for the information!
Regarding what kind of orifice, we are currently using a single stage, plate type of orifice (Flange). Thickness is 1/4 inch as per calculation and recommendation of pump vendor.

Regards,

b1

 

[rmw]

You are above critical pressure drop ratio, so you may have sonic velocity, with incumbent flashing, and/or cavitation downstream of your oriice. I have heard a few with this particular problem. Sounded like someone installed a jet engine in the piping.

An ARV has to take the same pressure drop, but their trims are designed to take it in steps so that each step is less than the critical pressure drop for that step of the drop. Check with your potential ARV supplier to find out how they propose to solve that problem, or install multiple breakdown orifices so that each operates above a critical pressure drop.

rmw