Title: Beginning of the System, Compressors
Course: Fluid Power Pneumatics (Sandbox) > Section: Module 4: Breaking Down a Pneumatic System / Air Delivery Side - 10 Hours

Start at the Beginning

Let's look at a system from the beginning. Here is the schematic that we have looked at before.

Reading the schematic from left to right, we see an empty triangle. This triangle represents the air supply coming into this particular system. In order to get air to this system, we would have to have some sort of an air delivery system. In a pneumatic system we would use a compressor to do this. Unlike hydraulic systems, where the pump produces flow instead of pressure, an air compressor produces pressure. The pressure is delivered to a tank, where it is stored. Flow in a pneumatic system occurs when there is a difference in pressure between two points.

Compressors

The following is the schematic symbol for a compressor.

Compressors come in all sorts of sizes and styles and are typically divided into two categories: Rotary and Reciprocating.

The two yellow compressors are piston compressors. These types of compressors are what you would find in most garages, small shops, and homes. A piston compressor is an example of a reciprocating compressor. Piston compressors are not as efficient and are typically louder than, lets say, a screw compressor (the third compressor). They are, for the most part, a less expensive compressor than a screw compressor of equivalent size.

The Coaire compressor is a screw compressor. This is an example of a rotary-type air compressor. Screw compressors are more efficient, quieter to operate and can deliver large volumes of air. Maintained screw compressors can deliver well throughout years of service.

No matter what type of compressor is used, all compressors must have some sort of driver, whether it be an electrical, a gas, or a diesel powered motor. Once the compressor part of the system is being driven, a compressor works by taking a large volume of atmospheric/ambient air and decreasing the volume, or compressing the large volume, into a small volume. Then, it takes that compressed air and stores it in a tank. There are a few things that happen when the compressor takes a large volume of air and compresses it into a small volume:

1. Heat in the system goes up. This happens because you are taking air molecules that were spread apart and compressing them closer together.
2. Pressure goes up.
3. Moisture can go up. This is because any humidity in the atmospheric air that is being compressed will be trapped and forced into the smaller volume. Remember, we are taking a large volume and compressing it into a small volume.

How a Screw Compressor Works:

Piston Compressor:

This is a typical piston compressor.

Look at the following diagram. It explains how a piston compressor works. The following diagram is a cut-away section view of the piston. This is similar to the pistons that would be found in the above piston compressor.

Let's go through the steps on how atmospheric/ambient air enters the piston area and gets to the storage tank:

1. In the diagram, locate the drive shaft. This drive shaft is connected to the electric motor. As the motor turns, the drive shaft turns. The drive shaft is connected to the crank shaft, which is connected to the connecting rod, which then moves the piston up and down.
2. On the left-side of the diagram, locate the air inlet valve. As the piston goes down, atmospheric/ambient air is drawn into the piston chamber. At the same time, the delivery valve is closed.
3. On the right side of the diagram, locate the delivery valve. As the piston moves up, the inlet valve is closed and the delivery valve is opened. The air is then delivered to the holding tank.
4. Once the air is delivered to the holding tank, it keeps building up pressure. This stored air can then be used in many ways.

Now that we have stored air, we can start looking at what we can do with that stored pressurized air.

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