Proportioning relay valve

摘要

A proportioning relay valve (10) includes a housing (12) receiving a relay piston (28) which controls communication between supply (14), exhaust (18) and delivery or outlet (16) ports. Control pressure is communicated to the relay piston (28) through a proportioning piston (58). The proportioning piston (58) is controlled by the pressure level at the actuating pressure port (22) to proportion communication to the relay piston (28) when the pressure level at actuating pressure port (22) is low and to permit unproportioned communication to the relay piston (28) when the pressure at actuating pressure port (22) is high. A bypass passage (80) and relief valve (86) also control the proportioning piston (58) so that unproportioned communication to relay piston (28) is permitted regardless of the pressure level at the actuating pressure port (22) when pressure at the control port (20) exceeds a predetermined value.