Compressors and Pumps

Let's go with dictionary definitions of each one first.

pump
noun
1. A mechanical device using suction or pressure to raise or move liquids, compress gases, or force air into inflatable objects such as tires.

compressor
noun
1. an instrument or device for compressing something.

Both compressors and pumps move fluids, and a fluid:

  1. Yields or moves from higher pressure to lower-pressure areas
  2. Has no distinct shape and takes up the shape of its container

Both liquids and vapors are fluids, but vapors (gaseous state) are compressible. Liquids are effectively incompressible. This means that a compressor is TECHNICALLY a pump, but a pump is not a compressor.

In both a pump and a compressor, a pressure differential is created between the inlet and the outlet. However, in the case of a compressor, there is a change of volume from inlet to outlet, forcing the vapor molecules into a smaller area.

While you can “compress” a vapor by forcing it into a smaller container, you CANNOT do this with a liquid without extreme pressures. (You can read more about that in this article.) This is why we must work so hard to ensure that liquid refrigerant stays out of a compressor because it will destroy it when the compressor attempts to compress it—unless the compressor is equipped with some method of providing clearance when liquid is introduced into the head.

In practice, most of the “vapor pumps” in our industry are compressors, and liquid pumps are just pumps or circulators but do not compress.

—Bryan

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.

Related Tech Tips

Techs are Under Pressure
The amount of pressure you're under depends on where you live. I live in Florida, so I'm very close to sea level. Therefore, the weight of the atmosphere is exerting exactly 14.7 pounds per square inch (PSIA) of pressure on every surface in every direction. There is no such thing as negative pressure—only pressure lower […]
Read more
Duct Leakage Can Be Costly
This tech tip was written by one of the best all-around HVAC minds out there: Neil Comparetto. I think that we all can agree that duct leakage is not ideal. Our job is to condition the space. If we can’t control the air, that becomes difficult. On top of that, anytime the ducts leak, you […]
Read more
An Evaporator Coil With No Fins?
Let's use a bit of imagination for a minute. Imagine you have two totally identical 3-ton systems. One of them is completely normal, and the other has no fins at all on the evaporator coil. They both have the same charge, airflow, and compressor capacity. What will be different in terms of readings and performance […]
Read more
loading

To continue you need to agree to our terms.

The HVAC School site, podcast and daily tech tips
Made possible by Generous support from