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dry silica gel, the humidity sensor
turns off the heat lamp, closes the
purge valve, and turns the dry air
circulation pump back on.
Fabrication
The improved engine dryer is
constructed on top of an approximate
2 quart, wide-mouth glass jar. All
electronics mount over or under the
jar lid. The lamp (heater) is suspended
below the lid in the desiccant as is a
custom-designed humidity sensing
capacitor. After a number of failures
by commercially available humidity
sensors (and many dollars spent on
several types), I was forced to resort
to my own sensor design. By using
a calcium sulfate (CaSO4) desiccant
material as a capacitor dielectric,
the failure modes of the commercial
devices have been circumvented.
Next you need a relay that
switches off the air pump, turns
on the heat lamp, and opens the
purge valve. The purge valve itself is
adapted from a silicone scuba check
valve diaphragm. Lamp heat drives
Lid with air tube/humidity sensor and lamp
out the absorbed moisture. When
the desiccant moisture content
drops, the humidity sensor will
switch it back into the engine
dryer mode. The pump injects dry
air into the engine crankcase via a
standpipe mounted in the oil filler.
Air venting from the crankcase
vent is recovered and returned to
the silica gel for re-drying.
The relay mounted on the circuit
board has termination lugs for the
120V AC power cord, the connection
to the pump power plug, and the
lamp. A wall plug socket is modified
with a cut in the connecting tang to
separate the upper and lower plugs.
This is done to provide a switched
power outlet for the air pump/heat
lamp and a continuous power outlet
for the power supply module used to
run the electronics.
The relay and printed circuit board
mount on top of the 3-inch diameter
