Can vapor line on truck be used for filling?

[molebleeze]

Hi folks,
We have a very hazardous chemical for bulk handling. At the end of the unloading (from the truck to the storage tank), the hose still has some chemical in it. We have difficulties to purge the hose to a safe place. (not able to purge to the tank for certain reasons). We then turn the head to the empty truck: can we purge the residual chemical to the truck via the vapor line on the truck top? Any comments?

 

[pierreick]

Hi,
Can you describe better your unloading process , transfer from truck to storage tank ! a sketch is welcome with the main equipment?
note : what is the material ?
Pierre

 

[LittleInch]

Do you not have sealing valves on the end of the hose?

I can't work out what you mean.

Needs a diagram and some more explanation.

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

 

[jari001]

I would also think you need the approval from the chemical supply company if you're going to do something non-standard activity with their truck?

 

[Latexman]

Why does the hose still have some chemical in it? That's the problem; solve that. We need a dimensional drawing with elevations to help you. A picture or three might help. What's the chemical?

Good Luck,
Latexman

 

[molebleeze]

Hi all, see attached picture, hopefully I make it reasonable.
The liquid needs constant temperature control, so the unloading pump is also used as circulation pump. We connect the hose to the truck liquid port and vapor hose to the vapor return port.
At the end of the unloading, the pump will not be able to suck completely dry the hose (it is a centrifugal pump). Therefore, the hose still has some liquid in it. We don't like the liquid stay in the hose. So would like to connect the hose to the vapor port of the truck and use the air blow to push the liquid in the hose back to the truck. [URL unfurl="true"]https://res.cloudinary.com/engineering-com/image/upload/v1631805434/tips/New_Bitmap_Image_2_nf23ia.bmp[/url]

 

[Latexman]

I doubt the sketch represents elevations too accurately. Is the pump in a flooded suction or a suction lift situation (when the truck just runs dry)?

Good Luck,
Latexman

 

[molebleeze]

It's a self priming centrifugal pump and is about 1 ft elevation below the truck. However, it just can't completely strip the hose and the unloading line.

 

[Latexman]

Sounds like it's loosing prime when the head gets so low. Is the liquid at or near it's normal boiling point, or has some dissolved gases in it?

This would be easier if you'd tell us what the pumpage is.

As you can tell, I'm not inclined to pressure push anything until the problem is well understood.

Good Luck,
Latexman

 

[molebleeze]

It is pumping liquid with properties close to water.

 

[3DDave]

If the tank is already vented then you have nearly 15 psi / 1bar to force liquid up. If that's not enough then how will adding more pressure help?

 

[Latexman]

Could the vapor return line be too small, allowing some vacuum to build in the tanker and some pressure to build in the tank? That could explain the issue.

If this has been developing/getting worse over time, can the vapor return line be plugging?

Good Luck,
Latexman

 

[pierreick]

Hi ,
Is it a new problem ?
Is the recirculation line in service during unloading?
You should talk to your chemical supplier about the best way to unload this type of chemical, they should have a lot of experience .
Is the technology of the pump the right one ? ,
You may lose the priming when the level is too low !
Do you have possibility to elevate the truck to add height to the suction , let say use a movable deck ?
Can you transfer under pressure instead of using a pump .

Again better to talk to someone familiar with your product and knowledgeable about unloading this chemical.
My view.
Pierre

 

[Compositepro]

You can use a small pump of a different style to remove residual fluid from the lowest point at the hose. An air operated double-diaphragm pump (AODD) is very well suited to this type of use.

Using compressed air to blow liquid uphill into a truck involves a number of well-known serious hazards.