Is Pocket in the LPG Booster Pump Suction Line Acceptable?

Good explanation....piss poor picture !

Zoom in.....You are too far away

Give us three views.....we are not familiar with the project

What color is the suction ?

Who did the NPSH calculation....What are the results ?

Is the liquid at saturation ?

You did evaluate the NPSHa vs NPSHr......right ?

It looks like the pocket would form in the pipe that goes up, over, and then down(?) into the pump. As far as I know, that's a big no-no. The inlet should go up into the pump, so any bubbles are sucked into the pump and eliminated. Pockets like this can cavitate the pump.

If they want access to a valve, can't the handle be on the down side?

Unless the fluid is really clean, valve stems pointing down are likely to gather grit around the stem/packing/seal. This is usually a no-no.

It might work to run the horizontal sections of the pump suction piping overhead, with valve stems horizontal and handles equipped with chain-wheels (possibly hammer-blow type for the 6-inch valves).

This could also eliminate a number of superfluous elbows.

From your picture:

As said by others, this is a no-no setup.

You can have gas trapped in the pocket (as you call it,) and make you lose suction. The suction pipe should be sloping down all the way from the main tank liquid side (bottom) to the pump suction port. This way, any gas formation will escape back to the main tank (this gas can form during idle periods).

With your existing setup, the gas will be trapped (and can form gradually even during operation) and eventually make the pump lose suction and run dry.

*** that is if the pump is centrifugal type ***

How did you get the gas to stay at the low point in the system?

The Gas will be traped between the pump inlet and the first down pipe before the pump! In the 'U' formed by the inlet pipe work, at the rising part towards the pump.

Don't you think so?

You manage to get the gaseous form to stay at a low point?

Seems like it would go to the pump suction as it tried to rise.

Then the pump will lose suction! it will stop pumping since it is meant to pump liquid and not gas.

This will need a priming of the pump... for sure ... out of experience and practice.

That I can agree with but the gas will not become trapped at the low point.

The gas can be traped at the high point just before the suction inlet of the pump (Copy the picture and ZOOM to see the details).

Also, if any gas is entrained into the pump, it will loose priming and some might even go out of the outlet (??) and get traped there (look at picture). You will have to be very wishing that the traped gas will be pushed Down the outlet exit pipework and then again UP...

The pipe work here looks more like a painting or art work than a fonctional design. The inlets and outlets are going to be a nightmare for whoever is going to be incharge of operation and trouble shooting.

My previous answer was in error. Since the supply is from above, the suction pipe should feed from above into the pump, Like LAA Lucke states.

Put the P&ID in order to understand exactly what is on your graph.

"so that in case of emergency there should not be any obstruction and for that they accept the pocket in the suction line".

If I understand correctly, this is already a case of emergency. Big time!!

What is your position (job description) in all this? I hope it is a lunch brake discussion you are having with a few colleagues .

A situation like this can not be handled or evaluated buy remote control (CR4). We would be culprits if anything would go wrong and it will, at the wrong time, wrong place, all of the time.

Stay safe, Ky.

First of all thanks to all of you for your valuable response to my query.

I am the lead piping engineer for the said Refinery project and this was commented by our client during model review session. As per your feedback, and with our process back up (with NPSHA and NPSHR etc), we convience our client, to not to have pocket in the suction lines.