FLUID FLOW CONTROL VALVE

摘要

1,273,297. Two-stage servovalves. SANDERS ASSOCIATES Inc. June 9, 1970 [July 1, 1969], No. 27960/70. Heading G3P. A two-stage servovalve for providing a flowrate to a servomotor independent of the load on the latter has a first-stage spool 15 adapted to connect high-pressure supply line 23 to either of the control lines 21, 22 of a pair of second-stage spools 41, 41' the space 53 between which receives fluid from line 23 via reducing valve 39. In operation, when spool 15 raises the pressure in line 21 or 22, the corresponding spool 41 or 41' shifts to connect the respective line 21, 22 to servomotor supply line 33 (spool 41) or 34 (spool 41') via a flow-path through the spool comprising a central, axial passage and a diametral passage, whereby control fluid eventually flows to line 33 or 34 at a rate sufficient to reduce the control pressure in line 21 or 22 to the pressure in space 53, the rate being independent of the load on the servomotor. The flow of control fluid is supplemented by a proportional flow from port 37 or 37' to line 33 or 34. The non-pressurized side of the servomotor is connected to exhaust by the operative spool 41 or 41'. In a modification, Fig. 4, the first stage is a flapper-nozzle unit 64-67 and the relay spools 71, 71' are arranged in opposing relation such that spool 71 controls supply and exhaust of the servomotor 77 when the flapper moves leftwards and spool 71' controls the servomotor when the flapper moves rightwards. In Fig. 6, a single second-stage spool 111 is used having a central land 114 co-operable with opposite ends of annular member 121 having, at each end, a pair of small radial slots (124) allowing land 114 to connect one of control lines 98, 99 to one side of actuator 106, and a set of larger radial slots (131-134) allowing land 114 to connect supply port 107 to the same side of actuator 106. In each case, a small deadband can be introduced by springs such as 117, 118 acting on the second stage spool(s). The pressure reducing valve 79 or 109 can be responsive to the pressure in control line 86 or 98 to maintain the pressure at supply port 78, 107 equal to the control pressure.