GB1260934A - Pneumatic control system - Google Patents

Abstract

1,260,934. Valves. ROBERTSHAW CONTROLS CO. 8 April, 1969 [8 April, 1968; 1 Nov., 1968], No. 17938/69. Heading F2V. [Also in Division G3] A comparator 13, Fig. 1, for interconnecting a pneumatic source 16, such as a vacuum pump or the intake manifold of a vehicle engine, to a pneumatically operated device 12 proportionally to the difference between two pneumatic signals imposed on a diaphragm 89, Fig. 6, of the comparator is characterized by means for automatically resetting the comparator to change the signal directed to the device 12 until the two signals imposed on the diaphragm 89 are equal so as to cancel the proportional actuation of the control device. In the preferred embodiment, the device 12 adjusts a heat exchanger 11 supplying the interior of a vehicle and is connected to atmosphere through a restriction 33 and to the comparator by a port 31 which communicates with a port 18 leading to the pneumatic source 16 to an extent determined by the position of the diaphragm 85. The pneumatic signals determining the position of the diaphragm are applied through a manually adjustable valve 15 and a thermally responsive valve 14 to spaces 93 and 94. Each valve is connected to the pneumatic source 16 and has a restricted connection 26, 30 with the atmosphere, the valve 14 being adjusted by a bi-metal element 78, Fig. 4, and the valve 15 by a screwed connection 48, Fig. 2, with a plate 50 in driving engagement with a rotatable stem 58. A capacitor tank 108 connected through a restrictor 103 in the diaphragm provides the automatic resetting or integral action of the comparator to prevent permanent offset due to changes in load on the system or to adjustment of the valve 15.