2 replies to this topic

[krishnamurthy]

why dont we require PSV for centrifugal pumps, i have searched thro online i studied centrifugal pump cannot create more pressure than it was designed for when the discharge valve is closed.please explain in detail.

[Art Montemayor]

 

 

You are correct.  The centrifugal pump is a dynamic device (as opposed to a positive displacement device); it cannot produce more head (or discharge pressure) than its performance curve shows.  I always tried to design my centrifugal pump systems by making sure that all related or attached piping and vessels had an MAWP (Maximum Allowable Working Pressure) rating that was lower than the pump’s discharge pressure.  That way, a pressure relief device was not required to protect the system from over-pressure.  I recommend the same technique to everyone.

 

Note that this does not protect the pump (and system) from the effects of maintaining a dead head (100% blocked discharge) on the pump for a prolonged period.  A pump should be protected from this event because damage can be caused to the seals and other related parts of the system.  How you do this depends on a case-by-case analysis of the pump system involved.  To discuss this type of protection to a centrifugal pump, one must have all the details of the pumping application and the pump’s characteristics.

 

[fallah]

Hi,

 

A centrifugal pump is normally protected against a dead head conditions by considering a minimum flow by pass line including a FV which activated by an dedicated FT to be set at a value, as minimum stable flow, specified by relevant vendor. Of course, if downstream piping/equipment are to be designed for pump's shut off pressure as maximum pressure the pump can generate, no PSV is required to protect the pump downstream.

There are the cases in which downstream piping/equipment aren't to be designed for pump's shut off pressure and to protect the downstream a PSV is needed to be set at design pressure of the weakest point along the pump downstream with the relief load of minimum flow already specified by vendor.