Skip to main content

Rules of Thumb

Power and installation:

  • For every horsepower, a compressor delivers 4-5 cfm (m3/hr), at 100 psi (7 bar) pressure .
  • A 50 HP air compressor can produce up to 12 gallons / 45 liters of water per day (with only 8 running hours daily).
  • Air receivers should be sized about 4 gallon capacity for each CFM of compressor capacity. That's 9 liters per m3/h in metric units.

For example, a small 20 cfm compressor needs an 80 gallon air receiver.

Costs and energy savings:

  • On average, compressed air costs about 30 cents per 1000 cfm (1700 m3/hr). This depends on the size of the compressor and includes electricity, purchase price of compressor and maintenance costs.
  • A 50 HP air compressor will cost you about 25.000 dollars in electricity cost per year (at 6.000 running hours per year).
  • Every 2 psi (0.15 bar) of pressure drop in your system will cost you 1% extra in energy cost (this adds up quickly!!!)
Pressure - Rule of Thumb

  • Lowering Compressor Inlet Air Temperature 10° F (5.5 °C) will result in a 2% energy savings.
  • A two stage reciprocating air compressor is about 15% more efficient compared to a single stage unit.


  • The typical discharge temperature of a rotary screw compressor (before aftercooler) is: 175°F or 80°C
  • The typical discharge temperature of a single stage reciprocating compressor is: 350°F or 180°C
  • The typical discharge temperature of a two stage reciprocating compressor is: 250°F or 120°C
  • In rotary screw compressors, every 18 °F (or 10 °C) above 200 °F (or 95 °C) reduces the compressor oil life by 50%!

The one rule of thumbs that amazes people the most is the amount of water that an air compressor produces!


Popular posts from this blog

Decoding the Duty Cycle Rating of Piston Compressors

Selecting the correct air compressor for your application can be a complicated process. Before making a purchase, operators need to specify the quality and amount of air their application requires. Each compressor technology (rotary, piston, centrifugal, etc.) has an optimal flow output, so users should choose compressor technology based on the compressed airflow requirement of their application. Some compressors, like rotary screw and centrifugal, are designed to run continuously at full speed while maintaining peak airflow (defined in cubic feet per minute, or CFM). The motors and cooling systems of these compressors are engineered to run 100 percent of the time without overheating. However, this isn’t true for all compressors. Piston compressors do not have the cooling capabilities to run continuously for extended periods of time. Therefore, each piston compressor must have a specified flow output and pressure, as well as the perc…

Did you buy the wrong type of compressed air dryer?

Do you have a desiccant compressed air dryer in your plant?
Do you know the annual running cost of that dryer?
It's plugged into a power socked, so it probably uses a bit of electricity… and you need to replace the desiccant every so many years. Right?
But for many types of desiccant air dryers, there's a hidden cost… and it is substantial!
In fact, the yearly cost will probably SHOCK you!
The culprit?
Purge air!
Purge air is air that is used to regenerate the desiccant. (the desiccant needs to be regenerated every few hours, to remove the water that it previously absorbed).
There are 2 main types of desiccant dryers:
Heated blower regenerated
This type uses an external blower and heater to regenerate the desiccant.

It requires only electricity (around 1 kW for every m3/min of compressed air).
Purge regenerated
This type doesn't use electricity to regenerate the desiccant...
Great, right! 
It uses precious compressed air!!!
This compressed air flow is between 10 and 20% of na…
Splash and Pressure Lubrication in Piston Compressors
Piston compressors have been around for centuries. They can be either oil-injected or oil-free, depending on the application and end use. In oil-injected models, the oil typically serves three crucial purposes: cooling, sealing and lubricating. But not all oil-injected piston compressors lubricate components the same way. There are two common methods of lubricating the pump in piston compressors: splash and pressure lubrication.

Splash lubrication In splash lubrication, oil is applied to the cylinders and pistons by rotating dippers on the connecting-rod bearing caps. Each time they rotate, the dippers pass through an oil-filled trough. After running through the oil trough, the dippers splash oil onto the cylinders and pistons to lubricate them. While splash lubrication is effective for smaller engines and pumps, it’s not a precise process. Parts of the pump may be insufficiently oiled or oiled too much. The amount of oil in the trou…