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What does liquid locking mean?
2

What does liquid locking mean?

What does liquid locking mean?

(OP)
Hi, I'm working on a project for a chemical producer to measure the electrical resistivity of a refrigerant in liquid form (under pressure). The chemists from the company included two valves at the top of the cell "to prevent liquid locks". Does anyone know what that means? Thanks in advance.

RE: What does liquid locking mean?

Liquid locking usually refers to a closed volume that that is completely filled with liquid with no vapor head space. Reciprocating pistons in engines that ingest liquid water or fuel can get liquid locked (or hydro-locked) where the engine cannot rotate because of incompressible liquid in the cylinder. A closed volume filled with liquid refrigerant is dangerous because expanding liquids can generate very high pressures.

RE: What does liquid locking mean?

(OP)
"The cell" is an enclosed cylinder with electrodes inside to measure the current. The refrigerant is fed into the cell through the bottom with these two valves at the top that I mentioned.

@Compositepro So you're saying these valves at the top are to ensure there is a vapor headspace within the cell by releasing some refrigerant from the top? And you're saying this is to reduce the pressure in the cell exerted by the refrigerant?

RE: What does liquid locking mean?

I do not know, could be. You have to be careful with tubing, as well, to prevent them from being sealed by valves when there is only liquid in the line.

RE: What does liquid locking mean?

Liquid locking anecdote:

Situation: three combustion turbine generators have been decommissioned and removed from site. Still remaining: one 1,000,000 Imperial gallon storage tank partially filled with #2 fuel oil.

What to do with the fuel oil?

Solution: run a 3" hose across the powerplant yard from the tank to the nearest ignition/combustion support oil storage tanks associated with a pair of coal-fired 300 MW generators. At the supply end, the hose is coupled to a gate valve on the storage tank outlet "Christmas tree." A handy shut-off valve is provided at the outlet end of the hose so the flow can be shut off promptly once the ignition oil tanks have been replenished.

Since it's the height of summer, I advise my supervisor my plan is to shut the hose outlet valve when fuel transfer is concluded but leave the supply valve open so that any expansion of the standing oil in the hose will relieve back into the tank. I'm subsequently told that's a bad idea, as in event of hose rupture there could be a spill of major proportions to the environment, and they don't want any spills at all, and by the way the direction is that I am to shut the valves at BOTH ends of the hose when fuel is not being transferred.

I allow the concern about a hose rupture is legit, but then point out that the oil trapped in the [black!] transfer hose will expand and burst the hose, and state that each time after closing the supply valve from the tank I will go back and re-open the outlet valve at the ignition oil tanks to relieve any trapped pressure.

I'm advised that us auxiliary plant operators are already spending too much time on this, and I'm ordered to do as I'm told.

A fuel transfer wraps up at around eleven AM. As ordered, BOTH valves are closed. The atmospheric conditions are CAVU, meaning ceiling and visibility unlimited...

At two in the afternoon or so, the hose bursts and delightedly spills its contents all over the yard...and us APOs are tasked with the job of cleaning up the resultant mess.

At least it wasn't a MAJOR spill...

Moral: liquid lock is real. Don't ignore the possibility of its occurrence.

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

RE: What does liquid locking mean?

I don't think we have enough information to be sure.

It's a bit of a strange phrase to use in the situation as described and isn't clear what they mean.

It's not clear how two valves will help prevent "liquid locks" without a proper description and drawing as the liquid is under pressure apparently. If you have a valve then someone will likely open it to vent the gas and fill the cell with liquid??

I wouldn't have called crshears incident liquid locking, just high pressure hose rupture caused by thermal expansion (by solar gain).

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

RE: What does liquid locking mean?

Quote:

I wouldn't have called crshears incident liquid locking, just high pressure hose rupture caused by thermal expansion (by solar gain).

There wasn't any vapour space in the hose, so I figured the liquid locking descriptor did in fact apply; does it matter any how the overpressure is developed?

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

RE: What does liquid locking mean?

Well a hose isn't supposed to have a vapour space...

Well yes, thermal expansion is known to a big issue as the pressure rise is commonly 3-4 bar per degree C. I's the thermal expansion or thermal pressure rise in a closed volume which is the issue.

But if you had a pump deadhead then it wouldn't overpressure it if it was rated correctly.

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

RE: What does liquid locking mean?

(OP)

Quote (LittleInch)

If you have a valve then someone will likely open it to vent the gas and fill the cell with liquid??

Yeah, when you open the top valve it releases the refrigerant which boils and leaves as a gas. The cell is filled under pressure as a liquid.

RE: What does liquid locking mean?

I think you will have to ask your friendly, neighborhood company chemists what they meant.

RE: What does liquid locking mean?

Hey j.doe, I don't see where you sent a pic of that portion of the drawing; is one of the valves simply a back pressure relief valve that will bleed any overpressure back into another portion of the contained system?

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

RE: What does liquid locking mean?

(OP)
@crshears I've attached a picture of the drawing, i don't think it's a relief valve, i don't know much about the subject but it just seems like a normal ball valve, both are the same. Maybe you're right though, i'll ask the engineers from the company. Thanks.

RE: What does liquid locking mean?

It's entering the wrong part of the valve according to that drawing. That is the symbol for a generic valve too so unfortunately doesn't help much.

Do you have a datasheet / part number for the valve to look it up? There should be a nameplate on the valve itself



Edit: I've just seen the other thread.

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