| 摘要 |
631,779. Automatic fluid-pressure control systems. BRITISH THOMSON-HOUSTON CO., Ltd., and BACHE, R. F. Oct. 16, 1947, No. 27766. [Class 38 (iv)] A mercury U-tube gauge provided with electrical contacts detects pressure variations in the delivery ducting of a blower or compressor and controls a reversible electric motor operating a discharge valve in the ducting. The gauge comprises a wide-bore tube 4, Fig. 2, connected at its upper end 6 to the point where the pressure is to be controlled, and mounted so that its height can be adjusted by screw 8. Its lower end is connected by rubber tubing 5 to a capillary tube t whose inclination to the horizontal is adjustable by rotation of the mounting 2. Three tungsten electrodes are sealed into wells formed in the bore of the tubing, the normal mercury level being between the top and middle electrodes. The control circuit comprises low-voltage relays 3, 4, Fig. 4, operated by D.C. from a transformer T and rectifier R, through the mercury gauge contacts. Contactors 1, 2 supplied from the A.C. mains L, N, under the control of relays 3, 4, operate contacts in the leads to the main and auxiliary motor terminals A1, A2 and Z1, Z2 respectively. When the lower electrode in tube t is connected to the centre electrode, only the motor is stationary, the circuit of contactor 2 being closed by contact 4a of energized relay 4, to open contacts 2b, c and d and close 2a in the circuit of contactor 1. At this time contactor 1 is unenergized, and all its contacts 1a ... 1d are open. If the pressure falls, relay 4, and hence contactor 2, are de-energized, contacts 2b, c and d are closed, and the motor operates in a direction to close the discharge valve. If the pressure rises, relays 3 and 4, and hence contactors 1 and 2, are all operated, contacts la ... 1d are all closed and contacts 2b ... 2d are open, and the motor operates in the reverse direction to open the discharge valve. For starting up, the manually-operated switch e energizes relays 3, 4, to open up the discharge valve before switching on the blower. The motor drives the valve through a reduction gearing and a flexible coupling by which limit switches f, g, hare operated to disconnect the motor in the extreme valve positions. When the blower is handling a gas other than air, the discharge from the valve may be connected to the inlet of the machine. |
