GB1395897A - Control system - Google Patents

Abstract

1395897 Fluid-pressure servomotor systems WEIR PUMPS Ltd 1 Sept 1972 [10 Sept 1971] 42256/71 Heading G3P A control arrangement comprises primary means 20, 21 for sensing fluid conditions at the discharge of a centrifugal pump 2 and generating signals proportional to the conditions, a comparator 11 for comparing a sensed signal value with a desired value from a regulator 23 and producing a control signal based on the comparison to actuate a regulator 12 controlling the operation of a steam turbine 3 driving the pump, secondary means, such as pneumatic trip switches 40 for sensing further operating conditions and a control device 9 for interrupting the control signal to the regulator when any of the further conditions are unsatisfactory. Static pressure is sensed at a point 16 in the discharge and the pressure drop across an orifice at points 17, 17. These are passed to a pneumatic controller 24 which is fed from a reduced pressure source 25 until the pressure developed by the pump is sufficient to trigger a snap actuator 26 and a gate 26A to supply full air-pressure. If an increased output from the pump is required, for example to supply more feed water to a boiler, a non-return valve 18 opens and the increased pressure drop between the points 17 ...17 causes the comparator 24 to open the regulator 12. The secondary means includes a plurality of fluid switching devices 28 .... 33 arranged in series in a conduit 8 and responsive, respectively, to turbine exhaust back pressure, pump water temperature, pump oil temperature, head available at pump suction 45 and the load on the pump. A manually operable valve 36 connects inlet 37 of a control valve 35 to the air supply source which then flows through the devices 28 .... 33 and exhausts through a selection switch 38 which additionally serves to bring the pump into operation if it has been on "stand-by". Exhaust air from the final device 33 is recycled to maintain the valve 35 and the switch 38 closed. A stand-by pump having a control arrangement exactly similar to that of Fig. 2A starts up automatically in the event of shut-down of the main pump. The switch 38 of the stand-by pump has a duct 40 to receive an airflow via line 41 from the valve 35 of the main pump circuit when the main pump is shut down so that port 39 communicates loop 8 with the line 41. Air is now directed via line 42 of the stand-by pump control circuit to the part 37 of valve 35 to pressurize the circuit 8 and start the stand-by pump. Relays 52 in the main and standby pump circuits sense the magnitude of the signal passing to a servo-positioner 14 and open a valve 32 to stop the pump if the load becomes excessive. A governor actuates a multi-port slide valve 53 and a discharge valve 15 to vent the regulator 12 if overspeeding occurs. The arrangement may be under the local control of a manual pressure regulator 57 or be remotely controlled by the valve 36 and the switch 38. Specifications 1371231, 1366895, 1360489 are referred to.