Patent GB-832826-A (GB)
Title: Improvements in or relating to differential pressure measuring apparatus particularly for measuring fluid flow
Inventor: DUBOIS ROBERT CLARK
IPC: G01F1/38
Filed: 1957-06-11
Abstract: 832,826. Fluid-pressure servomotor-control systems. MANNING, MAXWELL & MOORE Inc. June 11, 1957, No. 18391/57. Class 135. A differential pressure measuring apparatus comprises a pressure-sensitive means which acts on one end of a rigid elongate lever pivoted intermediate its ends, said lever carrying a rigid baffle which controls the discharge of air from a nozzle, the baffle-nozzle separation determining the pressure supplied to an indicating instrument and to a feed-back motor which acts on the other end of the elongate lever. As described, the fluid flow along a pipe P, P<SP>1</SP>, Fig. 12, is measured by a differential pressure device responsive to the pressures upstream and downstream of an orifice plate in the pipe. The device comprises a two-part casing D<SP>2</SP>, D<SP>3</SP>, Fig. 2, including a pressuresensitive capsule 23 connected by a link 30 to a rigid elongate lever assembly 31, 31a, 41, 42, Fig. 5, to which is attached a rod 52<SP>x</SP> the end 52t of which constitutes a baffle which controls the flow of air from a nozzle 70, Fig. 2. An auxiliary temperature compensating capsule 29 may be provided. The lever parts 31, 31<SP>a</SP>, are screwed together to clamp the centre of a diaphragm 32 the periphery of which is clamped to the casing so that the diaphragm forms a fulcrum for the lever assembly. The two arms 41, 42, Fig. 1, of the lever assembly are provided at their ends remote from the nozzle with extensions 41<SP>c</SP>, 42<SP>c</SP>, which receive the trunnions of a roller 46 to which one end of a proportional feedback bellows 49 is fixed. The other end of the bellows 49 is fixed to the central part of a U-shaped frame 52 the limbs of which are pivotally attached to the limbs 55, 55<SP>a</SP> of a second U-shaped frame 54, 55, 55<SP>a</SP>, secured to the plate 63 of the housing part D<SP>3</SP>. A rigid bar 43, Fig. 1, is secured to the ends of the arms 41, 42 and resilient blades 67, 67<SP>a</SP> are connected to the bar 43 and to projections 56, 56<SP>a</SP> of the rigid frame 54, 55, 55<SP>a</SP>. The blades 67, 67<SP>a</SP> resist longitudinal movement of the lever assembly 31, 31<SP>a</SP>, 41, 42. An air relay 74 is attached to the plate 63, Fig. 2, and comprises, Fig. 10, two diaphragms 76, 77 and a double valve and seat arrangement 82, 85 in a housing 75. The valve member 85 is urged to close the port 86 by a spring 88 and the member 82 is urged away from the member 85 by a spring 89. The housing 75 has four chambers 87, 80, 91 and 78. The chamber 87 is connected to the air supply and leads to chamber 80 via the diaphragm port 86. The chamber 80 is connected to the indicating instrument G, Fig. 12, and to the chamber 91, Fig. 10, via the passage 90 in the member 82 and is connected to exhaust at 92. The chamber 78 is connected to the chamber 87 via a restrictor and to the nozzle 70, Fig. 2. The angle at which the bellows 49 is located with respect to the lever assembly 31, 31<SP>a</SP>, 41, 42 determines the amount of feedback and adjustment of this angle varies the proportional band. Specification 790,294 is referred to.