Patent GB-197153-A (GB)
Title: Improvements in controlling means for motor driven pumps
IPC: F04B49/02
Filed: 1922-03-30
Abstract: 197,153. New British Electric Supply Co., Ltd., and Jacoby, H. C. E. March 30,1922. Controlling compression. - An electricalivdriven compressor is controlled by a switchoperating piston enclosed in a cylinder with its under side constantly and fully subject to the pump pressure and its upper or spring-pressed side alternately subject to pump pressure and atmospheric pressure. The upper cylinder space is first partially vented to permit initial movement of the piston and then more fully vented to permit a quick movement of the piston and breaking of the switch. An expansion chamber may enclose the switch-closing spring and receive the vented air. The movable switch contacts are insulated from, but carried by, a rod 4, which passes through an expansion chamber 5 into a cylinder 6 wherein it abuts against a piston 7. The upper end of the expansion chamber is closed by a cap between which and a collar 12 on the rod a spring 11 is provided. An opening 16 leads compressed air to the space below the piston 7. A port 18 communicates with the lower end of the cylinder, and a second port 19 communicates with the cylinder through a hole 20 in the piston wall when the piston is in its lowest position. A port 21 communicates through holes 23 in the partition 14 with the upper end of the cylinder, and a port 24 communicates with the expansion chamber. The ports 18, 21, 24 are continued through a valve casing 25 to a sleeve in which slides a piston valve 27; and the port 19 leads into a chamber 29 within the casing. The lower port 28 of the valve 27 is enlarged, and its upper part carries a stem 30 fitted with an adjustably spring- pressed collar and with a valve 33 adapted to close the valve casing. The valve 27 is formed with a port 35 which connects the ports 18, 21, 24 when the valve is in its lowest position, and with a port 36 which connects the ports 21, 22 to atmosphere when it rises and lifts the valve 33 opening communication with the spring casing 37 which leads to atmosphere through a port 38. The enlarged port 28 of the piston valve fits loosely in its sleeve, but is provided with a face 39 engaging a seating on the sleeve, so that leakage past the valve takes place only in the lower position. The chamber 29 is fitted with a vent valve 41 pressed upwards by a spring and having below it a leak 46 to atmosphere; a plunger 47 on the piston valve maintains the valve 41 closed when the piston valve is in its lowest position. The rod 4 is formed with grooves 13 which in its upper position connect the upper end of the cylinder 6 with the expansion chamber 5. The valve 27 may operate a switch through an arm 50 connected with its stem 30. In action, rise of the pressure to the maximum causes the valve 27 to rise and lift the valve 33, which vents to atmosphere any compressed air that has leaked past the valve. The valve 27 then quickly rises, further venting first the port 24 and then the port 21 through the port 36 and valve 33. The chamber 5 and the upper part of the cylinder 6 are thus vented, allowing the piston 7 to rise slowly until the grooves 13 connect them, when a sudden further rise occurs with breaking of the contact. At the same time the piston 7 closes the port 19, compressed air being entrapped in the chamber 29. When the pressure falls again sufficiently, this air leaks past the enlargements 28 of the valve 27 until the valve 41 opens and vents the chamber, allowing the valve 27 to descend under the action of its spring and of the reservoir pressure, closing the valve 41 and allowing air to pass to the chamber 5 and the cylinder space above the piston.