Vapour in LPG line

[dungun]

Hi, I have trouble every time to start the lpg pump. Before start I must prime around 20minutes before start the pump. Pictures - suction from spherical tank 12meter diameter, length around 12meter, size 3", temperature medium 12 to 45C, ambient 2 to 47C and suction strainer. Pump OH2 type. Some engineer suspect the line to long, strainer make the thing worst. Any Idea to solve??

 

[pmover]

what is the elevation difference between spherical tank nozzle and pump inlet nozzle?

-pmover

 

[rzrbk]

With the information given, my first guess would be a high point in the suction line. Either a vapor pocket in the line, or a suction line which dips below the pump can cause a similar problem in LPG.

If the suction line does not continuously rise from the pump to the sphere, then it cannot vent if it heats up faster than the liquid in the sphere, causing vapor to form and collect in the high point. Upon start-up this can gas-up the pump.

A line directly off the discharge bleeding back to the vapor space in the sphere can expedite start ups if this is the case.

While the long suction and strainer may not be ideal, if the pump eventually smoothes out and runs, I would say they are not the root cause.

 

[dcasto]

If the pump is sitting in the sun and it is just 1 Deg C warmer than the propane in the tank, the propane will flash and vapor lock the pump until all the piping and pump have been cooled down.

 

[jeap]

Could you be more specific on the priming method you're using?

 

[dungun]

Thanks All.
pmover - about 1.2meter (Total head available = 2.5m)
jeap - priming using vent to atm and P point back to the suction line (manually).
After all priming ok,pump smoothe and eliver 240MT/day. But starting make crazy!
The suction take from spherical tank to another farm.

 

[reena1957]

Dear dungun,
dcasto is right. It is not only the pump but also the long uninsulated suction line may be the culprit. Try insulating them as a first step. Second: dont recirculate back to suction line. It heats up the liquid even more. Try routing it back to the tank through another line Or rather to another tank if possible.
Best wishes

 

[jeap]

hi!

What reena stated is ok, but also avoid to vent to atm (to tank is ok) in the first step, or try to do it slowly. May be this sudden depressing is causing lpg in suction line to flash until the line is cooled down and it stops, but vapour pockets remain present in the line.

Line size (l and d) seems to be ok, I've seen longer suction lines working w/o trouble.