Air Pocket issue on pump suction

[ER_Azza]

Hi All

Rail car tankers are connected to pipework via 4" hose. This is to transfer fuel to the terminal fuel storage.
Unfortunately, inherent in the original design, after the NRV and valve, it step up to a 6" pipework.
A short pipework before the pump suction of the same 6".

There always seems a built up of air in the pipe suction.
Possibly carried over by the air bubble (?) through the system.
There is a vent just before the pump suction. The operator have to bleed the air several times throughout the pumping process to reduce air lock and increase transfer rate.
Is there a device or simple setup to remove the trap air on the SUCTION side.

(orifice is not an option in this case).

Thanks in advance

 

[TugboatEng]

You have a spring closed check valve on the suction inside of the pump. Your pump is likely struggling to prime against the check. Self-priming pumps will always struggle to prime against check valves and should have bypasses.

 

[LittleInch]

What is the orientation of the reducer at the pump suction - can you post a phot of that?

Pump suctions should be top flat if you've got a reducer there.

The issue with any auto air vent is that often the pressure in the pie is less than atmospheric in operation as the pump draws down the pressure to get flow from the rail cars, or maybe starts off positive then goes negative. The only option then is to rig up a float system with a vacuum line on top to suck out the air / vapour.

Is that NRV a spring loaded NRV or not?

Off loading systems like this often suffer from vapour being released from the fluid - what is it?, what temperature and now close are you to the vapour pressure of the fluid. If this is gasoline you're basically cavitating the pump is my guess.

Your best bet long term is to either lower the pump or use a can pump.

But first either observe from the suction guage or calculate what the inlet pressure is right before the pump when the tankers are at high level AND low level. If you don't have a suction guage, fit one.

Then give us the FULL picture and we might be able to help some more.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[1503-44]

Maybe butane, propane or LPG are especially problematic.