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Old 05-14-2010, 12:52 PM   #11 (permalink)
Bicycle Bob
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Join Date: May 2008
Location: N. Saskatchewan, CA
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Appliance White - '93 Geo Metro 4-Dr. Auto
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The one I built, which has been in use for years, is based on a rubber diaphragm. I think that the friction in a syringe would cause wide swings between on and off. I used a small,strong tin can from yeast, and bound the rubber drum-head on with windings of rubber strip. The vacuum hose fits on a soldered-in tube. The microswitch is bare, mounted on a hinge, and gets pushed into the drumhead by an adjustment screw. You could probably use a jar, and glue the vacuum hose into the drumhead.

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