PURPOSE:To make a fixed displacement discharge of nonpulsation securable, by designing a profile of each plate cam, driving each plunger of triple plunger pumps, in a way of prescribing the displacement to its turning angle. CONSTITUTION:Displacement diagrams a, b and c in each plate cam come to have an ascending region where displacement increases in proportion as a turning angle gets increased. Also it has a descending region where the displacement decreases in proportion as the turning angle gets increased. At both these ascending and descending regions, there are made so as to have an accelerating part, a uniform velocity part and decelerating part at every 60 deg.. A mutually crossed state of each of these displacement diagrams a, b and c comes to only two types I and II which alternate with each other at every 60 deg.. And, the displacement per unit turning angle of each of these diagrams a, b and c within the range of each state is specified. This specification makes the sum total of each displacement DELTAh1 and DELTAh2 of the accelerating part and the decelerating part and the displacement DELTAH equal to each other at every angle position. That is to say, a profile of a plate cam is designed so as to become an equation of DELTAh1+DELTAh2=DELTAH.
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