PSV superimposed back pressure calculation

[keyhanafshar]

Dear All,

I am having a Bellows type PSV with 3800kPa setpoint installed on a booster pump discharge line with nominal pressure of 3500kPa. The PSV discharge is relieving to booster pump suction which is under 600kPa constant pressure. Please assist me in calculating the back pressure in case the booster pump's downstream valve closed accidenatly results in pump deadheading to 4200kPa

May I say 4200kPa-3800kPa=400kPa which can not overcome to superimposed pressure of 600kPa results in locking the PSV or 4200kPa will be introduced to booster pump suction due to valve lifting.

Looking forward having your valuable comments.

 

[marvalar]

First you must calculate the superimposed back-pressure.

On this case, the super-imposed back pressure will be the shut-off pressure of the LP pump.

Then you must sum the built-up back-pressure.

The built-up back pressure is the pressure drop developed on the outlet piping at relieving conditions.

For its calculation you must check on the HP pump what would be the flow having:
Suction pressure = LP pump shut-off pressure
Discharge Pressure = SV set-pressure + Accumulation

Hope it helps

 

[keyhanafshar]

marvalar(Chemical)
Thanking you in advance for your reply

Still I am not clear. Say PSV discharge is connected to a pipework system witk constatnt pressure of 600kPa. If the PSV relieve at 4200kPa constant pressure what eill be the gauge reading at discharge. While assuming bellows type and system pressure staying constant for a while?

Will this high pressure applied to discharge size or just the differntila with set pressure will?

 

[don1980]

I suggest you find another way to protect from overpressure. This PSV is almost guaranteed to lift quite often. And, once it lifts it will stay open for a long time....possibly until you shut off the booster pump. Liquid PSVs require 15-20% blowdown, and your system doesn't provide that. You might as well have a restricting orifice.

As currently designed, this PSV will experience unnecessarily wear, waste energy, and possibly interfer with your flow control. Consider implementing a pump trip (with a short time delay) based on pressure, or use a power monitor to shut off the pump when it's deadheaded. The power monitor is the best and least expensive alternative.