GAS PLANT PROCESS

Thank you, Dear Guest, Second part of my question 1 was: what about the reciprocating pump? i.e. Is your reasoning(reducing the starting load due to use of block valve) right for reciprocating pump?

For question 2, In the case of centrifugal pump( or comp.), I agree with you. By choosing the down stream piping design press. Over the pump shut off press( or surge point ), There is no need to use of psv because cent. Pump will not capable to increase the press. more than its shut off head. But, my question was about how or mechanism of working of the reciprocating pump( or compressor). On the other hand, in the case of block discharge why dose the recip. Pump( or comp.) increase the pressure unlimitedly until something breaks? and having higher design press. doesnot help to this problem as the PSV always required, unlike the centrifugal one.

KAVOSH

Reciprocating pumps are "positive displacement" pumps. The simplest way that I can explain this is; what you suck into the piston has to go out the discharge on the return stroke. If it can not go out due to a closed valve then either the motor will stop or something must break.

You may not start a reciprocating pump with a closed discharge valve.

Think about is carefully, how could closing the discharge valve lower the starting load on the pump? It will suck in a fixed volume and will try to pump it out. Power = volume x density x g x head. As head approaches infinity so does power - something gotta break.

I think I am not yet clear how the head approaches to infinity as you said. The movement of the piston is done by the pump's driver(e.g., a constant speed elec. Motor). If the head depends on the capability of the driver having a definite power, then how does the produced outlet pressure get close to infinity?

KAVOSH

How clear do I have to make this? Reead my previous post - then either the motor will stop or something must break.

Dear Guest, thank you.

KAVOSH