GB1351709A - Fluid flow control device - Google Patents

Abstract

1351709 Fluid-pressure servomotor systems ROBERTSHAW CONTROLS CO 2 June 1971 [3 June 1970] 18585/71 Heading G3P A valve 28 controlling the supply of gas to a burner 10 is first moved to a partly open position when bleed flow takes place through two orifices 40, 62 between the main inlet 22 and outlet 24 and subsequently to a fully open position when flow takes place through the orifice 38 alone. The orifice 62 may be adjusted to vary the partially open position of the valve 28 and is controlled by a valve 72 which is closed by athermostatically operated lever 56 after a further valve 52 establishing communication with the outlet 24 through a pressure regulator 90 has been opened. The pressure created in a chamber 42 by the flow through the orifices is communicated by a passage 44 to the underside of a diaphragm for operating the valve 28. The angular position of the lever 56 is determined by an active bimetal element 86 heated by a coil 88 under the control of a thermostat 14 and connected by a bolt 84 to a compensating bimetal 82. When the demand for heat ceases, the thermostat interrupts the current to the coil 88 and the lever 56 gradually opens the valve 72 to increase the pressure in chamber 42 and partially close the valve 28. Further rotation of lever 56 closes both the valve 52 and the valve 28. The thermostat may be arranged to vary the energization of coil 88 is accordance with sensed heat requirements or to provide low and high voltage outputs in response to demands for heat at low and high rates.