liquid ring pumps compressors

[tomato5]

Hi! The subject is liquid ring pump/compressors:

1. Pumps and compressors have both been used with liquid ring design. Does this mean there are liquid ring pumps and liquid ring compressors?

2. If so, can they be identified from outside e.g. this is a pump, this is a compressor?

3. Usually pumps see liquid service, and compressors see gas. Is this not applicable to this type of equipment?

4. Is the intention to pull a vacuum, say in a vessel so the inlet pressure would be a certain vacuum but the discharge pressure would be a larger vacuum. If so, would the delta between the vacuum at suction and the vacuum at discharge be sufficient to maintain a flow

Thank you

 

[MikeHalloran]

1. Mechanically, they are pretty much the same device, with different names affixed, by custom, or for commercial reasons.
2. Therefore, no.
3. Liquid ring type pumps can move large quantities of gas, and at the same time, they can tolerate, and pass without damage, large volumes of liquid in the same stream.

One application that makes full use of their benefits is dewatering a Fourdrinier wire in a paper machine, where liquid ring type pumps are used to evacuate a stationary chamber underneath a fast-moving brass screen. On top of the screen is a suspension of fibers in water; as the water falls and is drawn through the screen, the fibers are deposited on the screen and become a nonwoven web, which is peeled off the screen, further dried, and eventually becomes paper.

They are also used in other processes where substantial gas flows at modest pressures or modest vacuums are required, and the presence of the sealing liquid (typically water) does not present problems of its own.

4. I do not understand your question.


Mike Halloran
Pembroke Pines, FL, USA

 

[Artisi]

Provided the vacuum on the discharge was lower than on the inlet I guess flow will take place, however I don't really understand, if the vacuum of the discharge side is lower than the inlet side - why do you need a pump?.

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.)

 

[GHartmann]

There is some degree of confusion generated by the common nomenclature.

A liquid ring compressor used in vacuum service is often called a vacuum pump.

It can also be confusing when talking about increased vacuum. An increased vacuum usually means increased negative pressure (lower absolute pressure). So be careful here.

Is there a practical reason for your questions?

 

[tomato5]

for ghartmann artisi mikehalloran
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first, thank you for your answers I will clarify some of your queries:

Your comments, to me, confirm that there is ambiguity/lack of clarity. Both the things are the same and yet they are not! We ourselves have a clear understanding when we can put that understanding on a piece of paper, have somebody read it, and then ask him you have read what I wrote, do you still have a question if he says no then you have it! many times we have things in our mind, thinking that we have the answer, and actually we don't
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mike, what is pretty much? so the very same physical piece of equipment can one day be a pump, and the second day a compressor?

yes you are right my last question about vacuum was badly worded i will correct below
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artidsi I will clarify this below
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ghartmann what happens when the liquid ring compressor is used in pressure service can it be used in pressure service

Yes we may be procuring liquid ring equipment for a project I have not done these before at all, I had these questions in mind so that during selection/vendor dicussions, I can make reasonably sane conversation
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now vacuum yes vacuum means pressure less than atmospheric but obviously not less than 0 psia 5 psia is 9.7 psig 11 psia is 3.7 psig 9.7 psig is a deeper vacuum than 3.7 psig

so, in vacuum service what might be say, inlet flange and discharge flange pressures numerically would both be vacuum? can the inlet be positive and the discharge vacuum? vice versa?

Thank you very much, again

 

[GHartmann]

Be careful with your pressure units; you are not following convention. For example:
3.7 psig = 18.4 psia

Express negative pressures by adding the term vacuum:
3.7 psi vacuum (= 11.0 psia)

Or better yet express the units in absolute pressure

For your equipment:
The equipment will be designed to "pump" either gas or liquid but not both
It would be unusual to pump from one vacuum to another (at some point the gas must return to the atmosphere)
You don't need a pump or compressor to go from a higher pressure to a lower pressure
Most vacuum pumps have negative suction / positive discharge

Do you have a specific application we can help you with?

 

[tomato5]

ghartmann thank you

your way of specifying positive and negative pressure is the right one

It sounds that you be a manufacturer and that is great. you also have clarified that it will be a pump for liquid and compressor for gas. Fine but what basically will be the difference in construction that will indicate compressor pump

pumps negative suction, positive discharge fine. what about compressors same, except that service is gas?

We are expecting a couple of projects with such pumps/compressors Yes, we would be happy to contact you once they are actually in what is your company?

I work for JGC America in Houston.

Thank you

 

[GHartmann]

I think I may have confused you. I am not working for a manufacturer. I just have experience with the practical application of compression equipment in the chemical process industry. This also includes liquid pumps for moving liquids.

Let's see if I can clarify:

A pump is generally a device for pumping liquid (transporting liquids from one location to another)

A compressor is a device for compressing gases
However, a vacuum pump compresses gases with suction under vacuum

See this page for liquid ring vacuum pumps:

http://www.gdnash.com/e-library/

Because centrifugal pumps and compressors act on the same principles they have some similar design features

 

[GHartmann]

Here is a guide to centrifugal pumps (for liquids):

http://www.mcnallyinstitute.com/home-html/Learning_about_pumps.html