Nothing really. There are PD blowers and PD compressors. There are dynamic blowers and dynamic compressors.
In general use, people tend to draw the line around 2 compression ratios (less than 2 CR is a blower and more is a compressor), but even that is subject to changing from application to application.
People want to pay less money for a blower, but that isn't always possible (something like a Roots Blower is a pricey bit of kit).
People tend to think of a blower as having atmospheric suction but a recent thread on eng-tips.com has pointed out that there are blowers with design suction pressure over 300 psig.
Hope this helps some, there really isn't an ISO committee on gas compression definitions (and if there were that industry would ignore them).
There is a rule of thumb to differentiate between blower and compressor. If discharge pressure is less than 7 psig, it is blower, otherwise compressor.
I tend to agree that there is no difference. Some people have used an arbitrary pressure ratio to define what is what.
However, I would suggest that a blower is a compressor whose final outlet is to atmosphere! A compressor is a blower whose final outlet is - some way - enclosed...!!
Going by the above... I would say that the device which I use to clean my yard of leaves is a blower. Another example of a blower would be the ID/FD fans of a fired heater...
The device which I use to pump air in to my bicycle tires is a compressor. Another example of compressor would be the pipeline compressor that brings natural gas to my home or a gas injection compressor that hides all our carbon sins underground...
Rotary,
That definition seems to work (I'd leave out the exclamation points, but that is personal preference).
We have a lot of devices marketed as "blowers" on wellsites to bump the wellhead pressures from near atmospheric pressure to 10-15 psig. They are marketed as blowers, but by your definition they are just another stage of compression. I think I can buy into your definition.
PD Blowers, two lobe or three lobe, are really conveying devices. They have no built in compression. If there is no back pressure on the blower discharge, there is no pressure rise across the blower itself.
Compressors actually do work as they have built in compression ratios. Some compressors are positive displacement type and some are dynamic type.
Blowers displace the medium (air or gas) and operate against back-pressure created in a given process. Compressors, however, feature built-in compression, which becomes more efficient around pressures of 1 bar (15 psig).
A blower could be viewed as a compressor, because of the general gas pressure rise between inlet and discharge, but a compressor cannot be viewed as a blower due to the higher gas discharge pressures that occur.
So, what is a blower? Normally, they are viewed as low or high volume, low pressure rise gas compression machines. Whereas a compressor, is either a low volume or high volume, high pressure rise gas compression machine.
Now if we're dealing in liquids, those are "pumps".
most transmission companies limit ratios across interstate pipelines to under 1.7 ratios, therfore all those huge gas turbine or engine drive compressor stations are blowers?
There is no definition except the one you adopt personally or in some anal company specification.
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