Flow through recycle line

[Ashjanj]

Hi,

Is there any rule of thumb for the preliminary sizing of the recycle line for a pump? If yes, at what percentage of the pump discharge flow is required to flow through the line?

Responce is highly needed.

 

[SeanB]

Is this a warm up bypass line or for minimum flow protection?

 

[JJPellin]

If the line is a minimum flow protection and used to allow start-up of the pump in pure circulation, then the line needs to be sized to pass the pump minimum flow. The obvious question to follow is "What is the pump minimum flow?" The pump manufacturer will provide a minimum flow for the pump. They have a vested interested in placing this value as low as possible so they can sell their pump for more services. Available literature has tables of values for minimum flow that are based on the suction specific speed and specific speed of the pump. These are more conservative and will generally keep you out of trouble. Someone on this site may offer a rule-of-thumb such as 25% of BEP. But this rule of thumb can get you in trouble. We have high speed Sundyne pumps that will cavitate themselves to destruction if you run them below 90% of BEP. And, we have low energy water circulating pumps that seem to run well at flows as low as 10% of BEP. There are too many variables to give a single, generic recommendation. You should research the literature on this topic and decide which method is the best fit for your particular pump in your particular service.

Johnny Pellin

 

[Artisi]

Good advice from JJPellin - "Someone on this site may offer a rule-of-thumb such as 25% of BEP. But this rule of thumb can get you in trouble."
Only the manufacturer can give you this information if it is not already shown on the pump performance curve.

 

[sshep]

From the standpoint of minimum flow for heat dissipation, the minimum flow required to limit the temp rise can be calculated from the fluid properties and the pump horsepower & efficiency curves.

best wishes,
sshep