Subject:
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Re: Pneumatic Air Compressor not working. Suggestions needed.
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Newsgroups:
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lugnet.technic
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Date:
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Wed, 6 Mar 2002 23:19:08 GMT
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Viewed:
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607 times
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One more thing that I forgot to mention. If you don't use the full stroke
of the pump cylinder when pumping, make sure you position the cylinder so
that you "bottom out" when the piston is fully retracted.
Air will only flow from the atmosphere into the cylinder if the cylinder is
at lower pressure. So when you extend the pump piston to draw in more air,
the highest pressure the air can reach inside the cylinder is slightly less
than atmospheric pressure (you lose some to the one way valve that lets air
in). When you retract the piston, the maximum pressure you can reach is
equal to that starting pressure times the volume of the pump with the piston
extended divided by the volume of the pump with the piston retracted.
Max Pressure = Atmospheric Pressure * Extended Volume / Retracted Volume
Since we can't do much about atmospheric pressure, the only way to increase
max pressure is to maximize Extended Volume / Retracted Volume. How is this
best done?
We can represent the volume of the pump with the piston fully retracted as
V1, and the volume with the pump fully extended as V1 + Max Stroke * Piston
Area.
Max Pressure = Atmosphere * (V1 + Stroke * Area) / V1
Our max stroke is fixed as soon as we decide what gear we will use to cycle
the pump, and the piston area is also fixed. So we can replace Stroke *
Area with a constant (c) and get;
Max Pressure = Atmosphere * (V1 + c) / V1
Max Pressure = Atmosphere * (1 + c / V1)
Now it is easy to see that you maximize Max Pressure by minimizing the value
of V1 (volume with piston fully retracted). And the way to minimize V1 is
to make sure the piston bottoms out when the pump is fully retracted. To
bad we can't take it all the way to zero. Infinite pressure!!!
Good Luck
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