The Effect of PSV setting to pump motor 1

[devaxrayz]

Hi all,

This question may sound very basic, but I need your opinion on this:

There is a reciprocating pump, 150 gpm with 25 psig discharge pressure (head: 60 ft) BHP: 3.7 hp and motor selected is 5 hp. The pump maximum pressure it self is 350 psig

I use PSV to protect the class 150 line and select 150 psig as the setting pressure. So the sizing of PSV is for 150 gpm relief rate and 150 psig pressure upstream of PSV.

If there is discharge blockage, the pump discharge will rise to 150 psig. I calculate the pump power requirement for 150 gpm and 150 psig is 22.32 hp (pump motor only 5 hp).

Here comes the question:
What happen to the motor and pump:
1. motor overload (possible to be broke)? or
2. the pump capacity will reduce to match the motor power capability (the rate down to about 35 gpm).

If poin no 2 is happen, wont my PSV size is too big (PSV sized for 150 gpm and the pump rate down to 35 gpm) and I will expect that the PSV will in frequent open and close at block discharge case.

thank you all




-rayz-

 

[quark]

Positive displacement pumps give more or less constant flowrates at any discharge pressure. Motor gets overloaded in your case.

 

[dcasto]

Make sure your pump is good for 150 psig for the selected pistons/plungers. I've seen pumps with ANSI 900 rating, but with the largest plunger the pump will go into rod load and break a crank. This is also true for the pumps maximum HP rating. You may need to look at setting the PSV lower if you do not want to risk a failure.

The motor will trip breakers somewhere over 5 HP too.