Improvements in or relating to unloading valves and unloading mechanisms for pumps

摘要

740,738. Rotary pumps. NEW YORK AIR BRAKE CO. Dec. 3 1953 [March 16, 1953], No. 33601/53. Class 110(2) [Also in Group XXIX] A continuously running pump of outwardly-sliding vane type is provided with :an unloading valve in the form of a differential piston 40, the smaller end 43 of which controls an unloading port 41 in a block 13 and is subject to the pumps delivery pressure acting in a direction to open the port 41, and the larger end 42 of which is subject to the pressure in an outlet communicating through a connection 34 with an "open centre" control valve, means, such as the passage 45 in the piston 40, so dimensioned as to develop a relatively low back pressure even at the minimum delivery of the pump being provided to connect the pump delivery with the cutlet. Thus when the "open centre" valve is in its neutral position, the pressure in the outlet falls and the unloading port 41 is opened. When the "open centre" valve moves away from its neutral position, the pressure in the outlet rises and the port 41 is closed. A relief valve 47 is arranged between the outlet and the pump reservoir. The unloading valve may be separate from the pump but as shown the block 13 is connected to a plate 9 with suction and delivery ports 26, 22 by bolts 12 which centre a ring 11 embracing an eccentrically mounted rotor 16 and into a head plate 8. The rotor is slotted to receive inclined vanes and is keyed to a shaft 15 mounted in bearings 14 and driven through a pulley 19 for example from the fan belt of a vehicle engine. The block 13 has a connection 29 with the exhaust of the "open centre" valve and this leads through a passage 28 open at 31 to the pump reservoir to the suction port 26. The pump reservoir is formed by a cuplike shell 32 secured to the block 13 by a screw 35. The delivery port 22 is flared towards its outlet and has branch ducts 24 leading to one of two circular grooves 25 open to the bottom of the vane slots. The ports 22, 26 have complementary balancing grooves 23, 27. The pump and its unloading valve are particularly adapted for parasite power systems operating vehicle steering gear, hatches, aircraft control surfaces. &c. Specification 589,349, [Group XXIX], is referred to.