(57) A reciprocating pump comprises three parallel connected plunger piston arrangements
and is driven via a cam mechanism (10) by means of a rotary driving device. In order
to insure a constant discharge, the cam mechanism (1) comprises three plate cams (14)
fixed on a common shaft (13) so that they are spaced 120 ° apart from each other,
the displacement curve (a1; a2; a3) of each plate cam has an ascending region in which
displacement increases as the angle of rotation of the plate cam increases, and a
descending region in which displacement decreases as the angle of rotation of the
plate cam increases, either the ascending region or the descending region including
an accelerating section in which displacement acceleratingly changes, a uniform velocity
section in which displacement linearly changes, and a decelerating section in which
displacement deceleratingly changes, the arrangement being such that the sum of the
displacement per unit angle of rotation in the accelerating section and the displacement
per corresponding unit angle of rotation in the decelerating section is equal to the
displacement per unit angle of rotation in the uniform velocity section.
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