GB1116412A - Flow-ratio controller - Google Patents

Abstract

1,116,412. Valves. GAS COUNCIL. 28 June, 1965 [30 April, 1964], No. 17923/64. Heading F2V. [Also in Division G3] Air and gas passages 10, 12, Fig. 1, each include an orifice 11, 13, respectively, whilst a detecting bridge 14, 15 comprising capillary or orifice flow resistors R-R4 is associated with orifices 11, 13 having two pressure tappings 16, 17. The areas of orifices 11, 13 are such that at the required flow ratio the pressure drops thereacross are equal in which case the resistors are of equal value, or in a predetermined ratio n, in which case the relationship between resistors is The pressure tappings 16, 17 may be directly connected to a valve to correct the flow rate through the passages 10, 12; the valve may be of the diaphragm or piston type used in conjunction with three flow resistors and a further source of fluid pressure to provide an amplified output to another pair of connections, the pressure of one of which is constant; the remaining connection may lead to the diaphragm of another valve in one of the passages 10, 12. The diaphragm may be weight loaded if the constant pressure connection is not used; the weight and diaphragm may be replaced by a governed source of constant fluid pressure. The above detecting bridge is applied to the control of the air/gas ratio to an air blast injector of a burner (33, Fig. 4, not shown), the pressure air passage 10 leading from an air valve controlling the burner output to regenerator (35) to preheat the air whilst the gas passage 12 includes a governor the outlet of which is at atmospheric pressure; air orifice 11 is fixed and gas orifice 13 is adjustable. The output of the detecting bridge associated with the orifices 11, 13 is amplified and directed to opposite sides of a diaphragm (38) controlling a tapered plunger regulating the effective area of the air inlet to the injector. After the bridge has been balanced the air/gas ratio can be pre-set by adjusting the throughput and orifice 13. The resistor R4 discharges to atmosphere to compensate for the bridge arm 14 and a further adjustable resistor (R5) is disposed in parallel therewith to compensate for leakage (37) from the valve connected to the tappings 16, 17 so enabling the bridge to be balanced.