A combination pump is a fuel pump with a vacuum pump attached. The fuel pump portion acts the same as just described but has a vacuum unit attached. When power is applied to the rocker arm by the eccentric on the cam shaft, the arm movement pushes the vacuum diaphragm down, expelling the air from below the diaphragm and forcing it into the intake manifold.
A combination pump
The same downward stroke enlarges the area above the diaphragm drawing air from the windshield wiper creating a vacuum.
As the rotating eccentric moves to its low point, the compressed spring is free to move the diaphragm upward expelling air from above the diaphragm into the crank case. The upward stroke draws air from the wiper into the expanded area below the diaphragm.
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When intake manifold pressure is low enough (when there is enough vacuum) the diaphragm is held near the center of its stroke by the combined effect of the spring pressure and the manifold vacuum. Hence, very little movement of the diaphragm is effected by the rocker arm.
Then this vacuum operates the wipers. When the vacuum is not great enough, the rocker arm, as stated earlier, forces the diaphragm down, expelling air into the intake manifold and is able to create enough vacuum to operate the wipers.
This article is only for Classic, Vintage, Antique or Old School cars – Please keep a comment below if there is anything else we should collect into our article.Its would be helpful for classic car users out there. Please check out for more info of Antique car models, Spare parts, Service and Other details.
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A combination pump is a fuel pump of Classic Cars Article Source : This article courtesy should goes to Auto Mechanics Autodology – Technical instruction manual by System Operation Support.