Figure 11-3.A typical two-stage reciprocating low-pressure air compressor.
(fig. 11-7). This unit consists of two impellers mounted
on parallel shafts that rotate in opposite directions
within a housing. As the impellers rotate, they trap a
quantity of air themselves and the blower housing and
move the air around the casing to the discharge port.
This action takes place twice each revolution of an
impeller and four times per revolution of both
impellers. The impellers are positioned in relation
between to each other by timing gears, located at the
end of each shaft and external to the blower housing.