difference between a blower and a compressor

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difference between a blower and a compressor

Postby walker » Tue May 19, 2009 9:39 am

There is the question:What is the difference between a blower and a compressor? Describe at least three methods of controlling the output of a compressor.
Should I expain the difference in general or I have to explain the blower which is fitted to the engine?What about of three methods of controlling the output of a compressor???

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Re: difference between a blower and a compressor

Postby walker » Tue May 19, 2009 11:19 am

Does anybody can correct this answer?

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.

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Big Pete
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Re: difference between a blower and a compressor

Postby Big Pete » Fri Jul 31, 2009 2:32 am

I think you have got it pretty well covered.
To me a blower would always be a rotary device, designed for large flow rates with a low differential pressure. Turbocharger, supercharger, Rootes blower, even an electric fan for aerating a sewage plant.
A compressor on the other hand, may be reciprocating or screw type, designed for relatively low flow rates with a high differential pressure and therefore may incorporate intercooling and or after cooling to improve efficiency and reduce weight.

Some of the ways of control would be: -

1) run the compressor continously and vent off surplus compressed gas through a safety / relief valve. ( wastes energy and causes unneccessary wear & tear on the compressor)
2) Manually start and stop the compressor according to indication on pressure gauge (which is what we used to do with start air compressors before UMS /EO but this requires machinery space to be manned 24/7)
3)Automatic starting and stopping of compressor, by pressure switch. (Pretty much industry standard)
4)Continuous running of compressor with automatic unloading controlled by pressure switch. (In the case of an Air Conditioning compressor this would be on SUCTION pressure)
5)Continuous running of compressor, with a variable speed drive, regulated manually or by a pressure sensor, to maintain constant pressure.

I believe some turbochargers now have variable geometry blades to improve efficiency at part loads, which I suppose is another way of regulating output, for a blower.

Good luck.
It is always better to ask a stupid question than to do a stupid thing.

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