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All cars use an electric pump-operated windshield washer with a
positive displacement washer pump. On some, the motor is placed in
the washer reservoir, while on others, it is driven by a wiper motor.
When the pump is attached to the wiper motor, the four lobe cam
starts a spring-loaded follower, but the pump does not operate all
the time that the wiper motor is running. This is because the pumping
mechanism is locked out and pumping action occurs.
A plunger is pulled toward the coil, allowing the ratchet pawl to
engage the ratchet wheel, which begins to rotate, one tooth at a
time. Each lobe of the cam starts the follower. The follower moves
the piston actuator plate and piston away from the valve assembly and
compresses the piston spring, creating a vacuum in the pump cylinder
through the intake valve. As the high point of each cam lobe passes
the follower, the piston spring expands, forcing the piston toward
the valves. This pressurizes the washer solution so it flows out the
exhaust valves to the spray nozzles.
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