Patent GB-877953-A (GB)
Title: Improvements in control systems for hydraulic actuators
IPC: F15B21/00
Filed: 1960-03-03
Abstract: 877.953. Hydraulic apparatus. GRATZMULLER, J. L. March 3, 1960 [March 6, 1959], No. 7533/60. Class 69 (2). Hydraulic apparatus for controlling the operation of a single - acting hydraulic actuator 13, Fig. 1, comprises feed and exhaust ducts 9, 10 between the actuator and a source 1 of high pressure and a low pressure receiver 3, and means 4, 16, 17 for selectively connecting the actuator to the source and receiver alternately, the feed and exhaust ducts being connected to the actuator by a combined feed and exhaust duct 18 having a volume less than the volume of liquid expelled from the actuator during its return stroke whereby air is purged from the system. The actuator may operate an electric switch and consists of a cylinder connected by the duct 18 to the ducts 9, 10, each of which is provided with a one-way valve 16, 17 and is connected to a duct 7 leading to a selector cock 4 which, in one position, connects the duct 7 to the receiver 3 and, in an alternative position, connects the duct 7 to an accumulator 1 charged by a pump 2. When the cock is moved to connect the accumulator to the actuator initially, the liquid passes through the line 9 compressing air in the actuator and in the duct 10, the valve 17 being closed by the pressure in the duct 7. Movement of the cock to its alternative position permits the piston 12 of the actuator to return to its initial position by the action of a spring and exhaust liquid and air through the duct 10 to the receiver, repeated operation of the cock eventually removing all the air from the system. The valve 16 in the duct 9 may be omitted or replaced with a throttle, or both valves 26, 17 replaced by valves controlled by a single or separate solenoids so that as the valve in one duct is opened, the valve in the other is closed. The valves may be replaced by a device adjacent the actuator consisting of a cylinder having a chamber 29, 32, 75, Fig. 6, connected to the ducts 9, 18 and 10 respectively. A by-pass valve 35 connects the duct 9 to the chamber 75 and is opened by the high pressure in duct 9 to permit the actuator to be operated, the pressure in chamber 29 moving a piston 30 upwardly to close a valve 31. When the duct 9 is connected by the cock 4 to a duct 33 leading to the receiver 3, the force of the spring returning the piston 12 to its original position causes the liquid in chamber 75 to move the piston 30 downwardly to open the valve 31 and exhaust liquid and air to pass through the duct 10. The duct 10 may be connected to an intermediate receiver at a higher pressure than the receiver 3. In an embodiment having two actuators 41, 42, Fig. 8, connected by racks to a gear 36 so that the pistons 39, 40 move in opposite directions, each actuator is operated by high pressure from separate lines 43, 44 and exhausts into a common line 62. Line 43 is connected to the actuator 41 by a duct 45a, one-way valve 46, and a duct 45b. The duct 45a is also connected to the chamber 50 of a cylinder so that when the actuator 41 is supplied with high pressure, a piston 51 closes a valve 53. When the line 43 is disconnected from the high pressure, the pressure of liquid exhausted from the actuator closes the valve 46 and opens valve 53 and the liquid passes to the exhaust line 62. A similar arrangement is provided for the actuator 42. Both arrangements for the actuators 41, 42 may be combined in a unitary structure having a body 64, Fig. 9, connected at one end to the duct 45a, at its centre to the exhaust line 62, and at an intermediate point to the duct 45b. The piston 51 is formed with the valve 53 and accommodated in a bore in the body 64 and contains the one-way valve 46. The opposite end of the body is similarly arranged for the actuator 42. Filters 70 are provided at the inlets to the body.