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Pressure
In general, pressure is the force applied perpendicular to an object’s surface per unit area over which the force is dispersed. It is often measured in pounds per square inch (psi), pascals or bar.
In air compressor systems, pressure measures the force that compressed air exerts inside the system — the right level matters for operating pneumatic tools, machinery and processes effectively and safely. Knowing about pressure and how much you need helps you choose the right system for your application.
FAQs
Pressure measurement usually uses a gauge that compares the pressure inside a system to the atmospheric pressure. You can also determine pressure using a formula. The formula for pressure is:
P=F/A
Here’s what each part means:
- P: Pressure
- F: Force
- A: Area
The imperial system uses psi units to measure pressure, which compares force in pounds to area in square inches. The metric system uses pascals, which compares force in newtons to area in square meters. Once you know the pressure in pascals, you can convert it to bars by dividing by 100,000. People use bars because 1 bar is slightly less than the current atmospheric pressure on Earth at sea level.
Air compressors generate pressure using air displacement. They mechanically force air through a chamber, where the system then compresses it. Pushing with a particular force in a specific area creates a higher pressure within the chamber.
Most air compressors use positive displacement. They pull air into the chamber, and internal parts reduce the volume to compress the air and increase pressure. Positive displacement compressors include:
- Vacuum or rotary vane
- Piston
- Rotary screw
- Scroll-type
Dynamic or nonpositive models speed up air to a high velocity using an impeller with rotating blades. Once in the chamber, the airflow is restricted, which causes the velocity to create higher pressure. Turbochargers in cars use these types of compressors.
When choosing an air compressor for your application, you must determine the optimal pressure range. Too high could damage equipment, create safety hazards and raise operational costs. Too low could prevent equipment from functioning or reduce the efficiency of your system.
To determine the ideal level for your application, start by identifying what tools your air compressor needs to run. Different pneumatic tools require different pressures. Pressure determines the power. As you consider pressure, you should note the airflow rate, typically measured in cubic feet per minute (cfm). The flow determines how much air you can move at a time.
You may hear various terms related to pressure in the context of air compressors, including discharge and rated pressure. Rated pressure is the operating pressure at which compressor performance is measured. In other words, it is the maximum pressure the compressor is designed to achieve. The manufacturer displays this value as a reference point for choosing a compressor that fits your needs.
Discharge pressure is the pressure produced at a particular point in the system under specific conditions, or the pressure at which compressed air leaves the compressor. This value represents real-life conditions. It is lower than the rated pressure due to internal pressure losses or component friction.
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