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The basic difference between blower and compressor is the pressure to which they can compress air.Blowers are designed to provide large volumes of air at low pressure and are most commonly used in conjunction with air diffusers.Blower simply displaces a volume of air from the inlet side to the discharge side and can operate against a back pressure of up to 1 bar.Blower is a device working its own to create positive pressure above atmospheric pressure or a vacuum.
Compressors are used to create pressures in the range of 100psi above atmospheric pressure.Multi-stage compressors can create pressures in the 1000's of psi.
There are two categories of compressor regulation: manual and automatic, and the elements needed to accomplish three basic functions:
1. Sense pressure changes
2. Relay pressure changes
3. Unloading mechanisms
With manual control, the compressor is adjusted by starting or stopping the driver,throttling the driver, or manually adjusting the capacity. In order to manually adjust the capacity, the compressor cylinders can be equipped with suction valve unloaders, suction valve lifters, and fixed or variable clearance pockets.
Мethod of controlling the output of a compressor with suction valve unloaders is a bypass control.
The unloader mechanism, attached directly to the suction valve, consists of valve fingers operating in the unloader cylinder directly on the valve strips. The spring-loaded fingers are forced to the unloading position. This mechanism, when actuated, holds the suction valve strips in the open position allowing the air to pass freely in and out of the suction valves without compression in the cylinder, thus reducing the delivered capacity of the cylinder and unit.
In automatic control schemes, the basic functions of sensing, relaying, and activating are performed by a combination of standard devices.Pressure switch-is a device which shuts-off the motor when the air pressure reaches to its maximum limit.
Valves are used throughout automatic control schemes to control and regulate the flow of air, water, and oil.