Liquid Ring Vacuum pump
Liquid Ring Vacuum pump
(OP)
Hi!
I've got an odd question and I'm not sure there is a definitive correct answer but I'd appreciate your postulations!
A customer uses a Liquid ring vacuum pump to create a vacuum in a vessel we supply.
Whilst carrying out a service on the vessel recently we were asked to inspect the pump as it was "noisy, and didn't work well" (It did pull a vacuum but was incredibly noisy)
Even though it wasn't our equipment, to placate the customer we examined the pump and found that:
a) the vacuum inlet (suction) line and water outlet (discharge)line we plumbed in reverse.
b) The pump was rotating in the wrong direction.
After a brief chat to the manufacturers to confirm our suspicions and we switched the pump direction and the mis-plumbed lines. Upon start up the pump now no longer pulled a decent vacuum, appeared to stutter and the motor got extremely hot to a point of smoking.
We undid our changes and tested the pump and it worked as prior to the changes.
The customer admits they've been using the pump in its current configuration on and off for six months, so my question is;
What is likely to have happened to the 'backward' operating pump during these six months that's rendered it useless when set up correctly...and can it be fixed (I'm guessing that its probably terminal) but we'd like to advise the clients...
I've got an odd question and I'm not sure there is a definitive correct answer but I'd appreciate your postulations!
A customer uses a Liquid ring vacuum pump to create a vacuum in a vessel we supply.
Whilst carrying out a service on the vessel recently we were asked to inspect the pump as it was "noisy, and didn't work well" (It did pull a vacuum but was incredibly noisy)
Even though it wasn't our equipment, to placate the customer we examined the pump and found that:
a) the vacuum inlet (suction) line and water outlet (discharge)line we plumbed in reverse.
b) The pump was rotating in the wrong direction.
After a brief chat to the manufacturers to confirm our suspicions and we switched the pump direction and the mis-plumbed lines. Upon start up the pump now no longer pulled a decent vacuum, appeared to stutter and the motor got extremely hot to a point of smoking.
We undid our changes and tested the pump and it worked as prior to the changes.
The customer admits they've been using the pump in its current configuration on and off for six months, so my question is;
What is likely to have happened to the 'backward' operating pump during these six months that's rendered it useless when set up correctly...and can it be fixed (I'm guessing that its probably terminal) but we'd like to advise the clients...





RE: Liquid Ring Vacuum pump
RE: Liquid Ring Vacuum pump
Another possibility is that you read the drawings wrong. I have worked with steam turbines from many manufacturers and thought that it was a universal truth that all turbine drawings and references were based on a view looking from the governor end toward the coupling end. However, I recently found a turbine manufacturer that has always referenced everything from the coupling end looking toward the governor. So, when we hooked up our counter-clockwise turbine to our counter-clockwise pump, the pump was spinning the wrong way.
Lastly, I would wonder if some of the external piping had been modified to accommodate the backward machine. I would compare the seal water piping, and controls to the P&ID to see if they changed something else.
Johnny Pellin
RE: Liquid Ring Vacuum pump
The rotating liquid ring is what does the compression, so if the rotor is capable of creating the liquid rotating ring, and the gas can flow through it, it will function.
I agree with JCPellin that it may be a case of two wrongs making a right if there was a wrong in the first place. I'd lean to a reference frame problem. It sounds like it was right (they will be noisy during certain operating conditions even when rotating in the right direction and plumbed correctly) and when you plumbed it to "right" it was wrong and pumping too much liquid, overloading the motor.
Keep investigating. Something out of sorts here.
rmw
RE: Liquid Ring Vacuum pump
Our liquid rings are two stage and I don't imagine that they would provide decent vacuum performance if plumbed and operated in reverse. According to their (generic) manual, such pumps can work as compressors, but in your case may have been overloaded due to the induced differential pressure.
"Noisy" can be due to cavitation. Lack of performance can be due to solids buildup within the vanes. Also incorrect seal water flow - either side of the ideal flow can see a drop off in performance. Interesting problem.
Cheers,
John
RE: Liquid Ring Vacuum pump
Many thanks for the replies. Heres some more info with regards to some of the queries posed;
The manufacturer's manual is a fairly poor affair and not much useful info is obtained when chatting to their engineers either.
The pump casing has the 'function' of each port cast into the back of the casing (quite tricky to spot unless you're looking for them) so we know what should go in or come out of each port.
We checked the rotation of the motor (after our adjustments) which was rotating in the correct direction (In the direction of another directional arrow cast into the casing)
Have to admit, one thing we didn't measure directly was the seal water flow. Other (cooling related) parts of the unit were seeing water flows of 6l/min and the unit needs about 4 to operate at its highest vacuum level so we assumed the mains water was sufficient to deliver the required rate but we did throttle it back to see if it made any difference.
The piping is a simple affair so no odd things could have been done; inlet water pipe straight from mains, vacuum line straight from vessel and water/air outlet pipe straight to drain.
We also added a vacuum breaker valve / bleed valve to the unit. (A suggestion from a totally different manufacturer whom we contacted in desperation) to try and reduce the noise.
RE: Liquid Ring Vacuum pump
David
RE: Liquid Ring Vacuum pump
I once worked with liq ring vac pump installation that was piped backwards as well. It discharged all of the seal water back into the process and pressured up the process. It did not pull vacuum on the process but tried to pull vac on the vent system (normal pressure discharge vent). Perhaps all of your piping is reversed.
RE: Liquid Ring Vacuum pump
But it is a band-aid in this case.
rmw
RE: Liquid Ring Vacuum pump
The principle is quite simple, a water ring given a reciprocating action in an elliptical shaped housing.
So the 2 critical items are the water seal and rotor vertical clearance. Things to check, Rotation speed correct, seal water supply to spec.
Offshore Engineering&Design
RE: Liquid Ring Vacuum pump
Johnny Pellin
RE: Liquid Ring Vacuum pump
RE: Liquid Ring Vacuum pump
I am wondering if you have solved your dilemma with your customer's LRVP?
If not, can you provide me with the make and model of the unit in question and perhaps I can help. These are very simple devices and when installed/operated correctly they are very reliable units.
JAK
RE: Liquid Ring Vacuum pump
another thing: the noise is probably from cavitation, which is dependent on the temperatures in the pump.
What temperature is your "vacuum" and what temperature is your seal water ?
Important is, that the temperature of your seal water is as low as possible, which helps in volume flow and decreases cavitation.
RE: Liquid Ring Vacuum pump
Best regards Morten
RE: Liquid Ring Vacuum pump
the LRP i encountered (Gardner Denver aka Nash aka Elmo) do have liquid inside the casing, because it acts as the "piston" pumping the air.
Cavitation can occur, if the temperature of the air is much higher than the temperature of the liquid, in which case some local cavitation takes place.
best wishes
Alex. Slanina
RE: Liquid Ring Vacuum pump
rmw