Difference Between Pumps and Compressors

Couldn't have put it better myself. GA!

I'd go with that. My way of saying it is a pump usually moves something at a steady rate. A compressor however is working against varying loads to achieve a certain pressure. Two different concepts.

First of all, to clear up definitions, gases and air are fluids, as are liquids. I believe your intention is to differentiate between gases and liquids.

The simple answer is that it is a matter of pressure. An airpump or gas pump becomes a compressor beyond a certain pressure (and becomes a blower beyond a certain flowrate), but I don't know whether or not this point is strictly defined anywhere. A liquid pump never becomes a compressor because liquids are not compressible, although very high pressures can be achieved.

Your duty requirements (fluid, flow, pressure, etc.) will determine whether you require a pump or compressor. There is a huge variety of different types of pumps and compressors for all sorts of applications, but in some instances they look the same.

Excellently put by Kramarat, but generalizations always involve exceptions. This is an interesting one (definitions are always fun, aren't they!), and I'd be interested to hear what others think.

There are some compressor applications where the fluid doesn't have to be conveyed from A to B at all (eg pneumatic systems/actuators), and the purpose of the compressor is purely to supply pressure. There are other compressor applications where flow is part of the equation, and it won't achieve its' purpose if there is no flow (eg the compressor stage in a jet engine, or compressors supplying to pneumatic tools).

There are a lot of blowers and compressors used in process industries, and what differentiates the applications is usually pressure not flowrate. They both have to move air (or other gases).

Conversely, there are pump applications where the purpose of the pump is to provide pressure, not flow. I'm thinking particularly of hydraulics pumps where the purpose is to provide pressure in a closed circuit to drive a hydraulic motor or actuator, not to move fluid from A to B. In fact, it does exactly the same job as many compressors, but obviously can't be called a compressor because the fluid is not compressible.

So for liquids it will always be a pump, never a compressor. But for gases it could be either a pump or a compressor, and it seems to me that the difference ought to be determined by pressure rather than flow. I'm quite happy to be convinced otherwise if I'm wrong.

Call me simple.. (not now Holzfella!) but is the answer not in the name of the things we are talking about, a pump pumps things, while a compressor compresses things???

A diesel pump... an air compressor!

Yes! Simply:

• A pump is used for both liquids and gases.
• A compressor is used only with (compressible) gases.
• A compressor cannot be used with liquids (because they are incompressible).

You could be right, or perhaps sometimes the names are not entirely appropriate.

A hydraulics pump is not used for conveying a liquid from A to B, it is used to pressurize a working fluid. It doesn't really pump anything anywhere, so perhaps it should be called a 'Pressurizer' rather than a pump.

Some compressors have the actual job of compressing a gas, eg a refrigeration compressor or a compressor for for converting natural gas to LNG. But for some other compressors the main purpose is not to compress, but rather to convey a certain quantity of gas from A to B at a certain pressure (I'm thinking particularly of factory air systems for driving pneumatic tools). So perhaps these compressors should really be called 'Pressurizers'?

A hydraulics pump is not used for conveying a liquid from A to B, it is used to pressurize a working fluid. It doesn't really pump anything anywhere.

not trying to be picky.... but when a control valve is opened, hydraulic fluid passes thru that valve to the cylinder which fills up with fluid, yes pressured fluid, from the tank via the pump to move the piston inside that cylinder either in or out.

So does it not pump fluid to somewhere.. (given not all the time, as it maintains pressure on the pump/pressurised side of the control valves)... when a control valve is operated so a piston actuates??

And on vacuum, it's always a vacuum pump, never a compressor, though it is compressing.

Good point, and interesting to note that liquid ring vacuum pumps and liquid ring compressors are exactly the same animal.

Refer to the following article that explains the main differences in details:

What are the Differences Between a Pump and a Compressor? Pumps vs Compressors (PDF) – What Is Piping