2 replies to this topic

[sukubutsu]

Hi there,

 

I am currently sizing a relief valve downstream of a centrifugal pump for a blocked outlet case. In the previous company that I worked for, it was standard to use the rated capacity of the pump as the relieving rate of the PSV.

 

In my current company, it is argued that for the centrifugal pump, the relieving capacity should be the corresponding flowrate at the relieving pressure located on the pump's curve. I had this same argument as well when first presented with this calculation with my old company but I remember reading about this somewhere that it is standard practice to use the rated capacity of the pump (I cannot remember where I've read this)

 

Can any experts advice me on which relieving rate to take for sizing the PSV? And could you also point me to any literature or standards to back up your stance?

 

Thanks in advanced

 

 

[demank]

On the GPSA section 5, Relief System, it states:

"the relief load is usually the maximum flow which pump, compressor, or other flow source produces at relief conditions."

 

Also API STD 521, para 5.5 state:

"The quantity of material to relieved should be determined at conditions that correspond to relieving conditions instead of at normal operating conditions. The required relieving rate is often reduced appreciably when this difference in conditions is considered."

 

So, I agree with your current company.,

Edited by demank, 30 October 2013 - 12:20 AM.

[fallah]

sukubutsu,

 

If the centrifugal pump curve isn't available it is better to get the pump rated capacity as PRV relief load...

 

If the pump curve is available, PRV for pump protection or for downstream equipment protection can be set at the value between corresponding pressure of pump rated capacity and corresponding pressure of pump minimum stable flow by backing up on pump performance curve in order to reduce the PRV capacity and size. In any case the PRV set pressure shouldn't be lowerer than 1.1 times (at least) the normal pump discharge pressure to prevent PRV opening at the situations near the normal operating conditions...