| 摘要 |
<p>The present invention provides a piston assembly comprising a primary piston (12) and a co-centric secondary piston (14). The pistons (12, 14) are received within a housing (10) for reciprocating movement therein and relative to each other. The housing (10) and the pistons (12, 14) are arranged for operating pressure to be applied to the secondary piston (14) so as to drive both pistons (12, 14) within the housing 10. The secondary piston (14) is provided with means (114) enabling the operating pressure to be equalised across the secondary piston (12) and at least one bypass passage (13) extends through the secondary piston (14). The arrangement is such that upon completion of the stroke of the pistons (12, 14) pressure equalisation occurs across the secondary piston (14) which causes the pistons (12, 14) to separate. The bypass passage (130) becomes fully operable subsequent to pressure equalisation, whereby a fast return stroke is achieved.</p> |
