22 has port 24 through which fluid enters cylinder 22 and outlet 32 through which fluid exits cylinder 22 in addition valve 25 forms a seal within cylinder 22 valve 25 is a poppet valve comprising plug 42 plug spring 44 and plug spring platform 46 plug 42 is a plug shaped and sized to seal cylinder 22 against fluid passage when retained in place as shown by valve spring 44 valve spring 44 is a low strength spring which extends from plug 42 to plug spring platform 46 and restores plug 42 to a sealing position in the absence of other forces plug spring platform 46 includes holes or fluid passages not shown to allow fluid to flow through spring platform 46 toward outlet 32 in one embodiment plug spring platform 46 is threaded to fit into threads in outlet 32 the threaded interior of cylinder 22 also allows threaded tubes and hoses to be attached at outlet 32 rotation of cam 12 drives piston 16 back and forth along piston axis pa as described previously straight shaft 18 sometimes blocks port 24 closing port 24 and preventing fluid from exiting cylinder 22 save by outlet 32 while piston 16 moves to the left from its rightmost extension within cylinder 22 valve 25 seals cylinder 22 preventing fluid from exiting seal 22 via outlet 32 the movement of piston 16 creates a partial vacuum between piston face 21 and plug 42 of valve 25 valve 25 is retained in a seal by seal spring 44 and by vacuum movement to the left by piston 16 withdraws straight shaft.