Patent GB-1129520-A (GB)
Title: Improvements in or relating to fluid flow control devices
IPC: H03K3/351
Filed: 1965-11-22
Abstract: 1,129,520. Valves. MONSANTO CO. 22 Nov., 1965 [23 Nov., 1964; 6 May, 1965; 24 May, 1965 (2); 15 Sept., 1965], No. 49491/65. Heading F2V. [Also in Divisions G1, G3 and H3] The effective opening of the electro-magnetic cally actuated valve A is modulated in response to changes in a physical variable by controlling the voltage to the coil 3. Power is supplied from A.C. source 36, 38 through a silicon-controlled rectifier 40 of which the gate electrode 42 is controlled by a relaxation oscillator comprising unijunction transistor 46, capacitor 52 and resistor 55. The oscillator is synchronized with the supply by a square wave control voltage produced by diode 56, resistor 54 and Zener diode 58. The physical variable can be represented by a control resistor 45 which in conjunction with capacitor 52 determines the firing time of transistor 46. As the control resistance is decreased from a critical value rectifier 40 will conduct for increasingly larger angles. Both the maximum opening force on the valve plunger 18 against spring 13, and the effective pulse width are varied. This causes a forced vibration of the plunger on and off its seat which determines the effective valve opening. The circuit includes a thermistor 43, a temperature compensating resistor 53, and a surge suppressor 57. The valve plunger is fitted with a seat comprising a stainless steel insert 28 with a plastics sleeve 29. This reduces rebound. The plunger is guided so as to seat constantly in the same place. For liquid level or pressure control, a cadmium sulphide resistance type light-sensitive transducer (90), Fig. 4 (not shown), takes the place of control resistor 45. This senses changes of level in a tube (92), or changes of pressure when a control flag connected to a pressure gauge controls a light aperture. Proportional band adjustments are provided by a coarse adjustment potentiometer (95) and a fine adjustment potentiometer (96) which serves to re-set the flow rate. In Fig. 5 (not shown) a main valve (81) is controlled by a pilot valve (V) constituted by the valve of Figs. 1 and 3. Valve (V) is downstream of a fixed orifice (84) between the inlet and outlet of the main valve which is responsive to pressure upstream of the pilot valve. A differential pressure feedback loop may be used to maintain a fixed drop across the main valve. Or the main valve may be positioned using a feedback loop wherein an iron rod fixed to the main valve varies the inductance of a coil. The control valve may be used with a fixed orifice (60), Fig. 8 (not shown), on the downstream side, whereby there is an internal negative feedback owing to pressure on the plunger (18). The device in this form may constitute a stable resistancepneumatic transducer with a linear characteristic. In Fig. 10 (not shown), the pressure drop across an orifice (101) is measured on an electrical readout device (106) receiving an output from the solenoid coil (105) of the control valve (A) which is connected across the orifice. In Fig. 11 (not shown), the plunger (18) has two axially spaced sealing rings (131, 132) and a pressure equalizing passage (133). In operation, these rings are flexed without sliding and the axial rebound characteristic is damped. This is stated to avoid the need for a quiescent period between each succeeding force pulse, and to allow the use of a variable amplitude sine wave voltage instead of the waveform produced by Fig. 3. The control valve may have a conical closure (223), Fig. 16 (not shown), seating on a conical plastics seat (237), or a loose ball valve (291), Fig. 20 (not shown) may be interposed between this seat and the plunger. In a further embodiment, Fig. 22 (not shown), the control valve is biased as shown toward open position and the flow is modulated by varying a pulsed D.C. current to the coil through the circuit of Fig. 26 (not shown). In operation, the plunger (317) is, on average, held against the seat (316) but vibration off the seat is permitted by the current reduction accompanying the so-called "negative pulses". The plunger carries a seat ring (325). Modifications of this seat are disclosed, Figs. 24 and 25 (not shown). An analysis of laboratory test results is included. The valve of Fig. 5 may be used as a pressure reducing valve, in which the reduced pressure is set by adjusting the variable resistor 45, Fig. 3.