Any ideas? 1

[SNOW111]

We have a 250m3/h pump for onloading petrol from the tanker ship to the deposit. While we try to empty the deposits once the fuel is at the lowest level, air enters inside of the pumps and the pump gets stuck. Please give any ideas why that happen and what type of pump do You suggest to use to avoid this problem?
Any answer is appreciated.

Best regards

 

[Artisi]

Without a lot more detail on the complete installation, configuration and pump type being used not easy to give any real solution - however, a two pump installation might help, the initial pump run until the inlet entrains air at which time revert to a smaller pump unit, either selfpriming, positive displacement or a peristaltic hose pump to mop-up the remaining fuel.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[LittleInch]

You might be pulling a vacuum in the pump caused by high temperature of the fluid. Petrol has a very low margin in many locations were even a few metres of lift from fluid level to pump inlet can cause a vacuum to form.

We need details such as a profile drawing showing liquid level, nozzle level, pump level and temperature, pipe size,flow rate etc to give any more assistance, but artisi has the basics nailed.

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

 

[bimr]

To completely empty a tank, the tank need to be designed to have a sump that permits total drain-out of the liquid from the lowest point. Where a pump is mounted above the liquid, it will probably cavitate at tank liquid levels. For an tank unloading pump installation it is best to install a buffer tank between the tank and the pump to let the road tank completely drain-out before the pump starts cavitating. Tank load-out pumps must have a very low net positive suction head requirement.

The unloading criteria should have been a design requirement for the tank system

 

[SNOW111]

Dear All,
Thank you for your answers.
We cant switch into using 2 pumps. Unfortunately that is not an option.
Please advise if a rotary lobe pump could work without any problems regarding the air suction part?

Best regards

 

[rajm008]

hii,

In ship i dont know if its possible to empty the tank completely , As far as i know there would be some unpumpable amount left. below the suction . One thing you can do is adjust the trim of the ship. to get the max out of the tank.

 

[georgeverghese]

This "air" may actually be high vapor pressure gasoline vaporising in the suction line due to high suction lift and pump NPSHr > NPSHa. Once vapor breaks out in this suction line, gas fills the pump casing and flow ceases ?