Patent GB-460567-A (GB)
Title: Improvements in and relating to control devices for fluid distribution systems
IPC: G05D16/16
Filed: 1935-04-23
Abstract: 460,567. Fluid - actuated valves; Venturi meters. TRIGGS, W. W. (Pittsburgh Equitable Meter Co.) April 23, 1935, No. 12151. [Classes 69 (i) and 135] In a flow controller for gas mains, the pressure difference produced by an orifice plate 15 in the low pressure main 2 is increased by means of a Venturi tube 22 one end of which is located at the vena contracta of the orifice and the point of increased pressure difference at the throat of the Venturi is connected by a conduit 21, 42, 41, 32 containing a control chamber 57 having one or more control valves 40 with a point in the main 2, a further conduit 60 leading off from the control chamber to the pressure-responsive diaphragm 7 actuating through a lever 4 a main valve 3 which cuts off the high pressure main 1. By means of pipes 80, 81 the pressure difference may also be used to actuate any conventional type of differential pressure flow meter 75. The plate 15 and the Venturi 22 are mounted in a narrow cylindrical member 11 between the main 2 and the controller casing 2<1>. The Venturi which is made in two parts screwed together is supported by a tube 21 passing through the member 11 into a ported body member 36. A tube 32 concentric with the tube 21, is screwed to aT-piece 35 connected to the member 36, and communicates with the main by a passage 29. The control chamber 57 is formed in the member 36 and restrictions 38, 49 at its ends are controlled by a shuttle valve 40 which can be set by means of a graduated member 52 supported in a bonnet 45. The connections 80, 81 to the meter are connected to the member 36 and the T-piece 35 respectively. Further connections 61, 62 lead to a safety regulator 67 comprising a spring-loaded diaphragm-actuated valve 66, Figs. 1, 4, which opens when a predetermined maximum pressure has been attained in the main 2 whereupon the main valve 3 closes. The arrangement is shown diagrammatically in Fig. 4. With the restriction 49 closed, the chamber 57 and hence the loaded diaphragm 7 is exposed to the full pressure difference produced by the venturi and the orifice plate. The valve 3 therefore opens wider so that the increase of pressure or " boost " in the main on increased demand, over the normal pressure when the demand is a minimum, is then a maximum. As the restriction 49 is opened and restriction 38 is closed, so the available " boost " is decreased. As the pressures in the conduits 80, 81 vary for different settings of the valve 40, the meter readings have to be multiplied by a coefficient depending on the valve setting. Calibrating apparatus for determining these coefficients and other coefficients from which the " boost " for each valve setting is determinable comprises a conduit 101, Fig. 9, in which a constant flow is maintained, the flow being determined from the reading of the manometer 103 and the known constant for the orifice plate 104. The connections 80, 81 are replaced by the arms of a manometer 112 and a third manometer 106 is connected from the chamber 57 to the main. The manometer 106 measures the " boost directly. By means of the corrected meter readings it can be seen whether one or more of the controllers in a distribution system is carrying more than its share of the load, and by means of the valve 40 the " boost " may be adjusted to correct any unfair loading. In a modified form, the Venturi is located on the downstream side of the orifice plate 15, its inlet end being located at the vena contracta of the orifice.