GB744620A - Improved testing device for fluid pressure gauges - Google Patents

Abstract

744,620. Testing pressure gauges. PRESSURE GAUGES, Ltd. April 9, 1954 [April 9, 1953], No. 9682/53. Class 106 (2). A deadweight tester for fluid pressure gauges comprises a pair of piston and cylinder units 29, 19 and 28, 18 of different internal diameters rigidly mounted substantially coaxially at opposite ends of a bore 17 in a body 16 with mechanical interconnection 31 between the pistons and means for applying a predetermined endwise loading to one piston, the piston and cylinder units being made of materials having thermal coefficients of expansion differing so that the difference of the effective areas of the piston and cylinder units remains substantially constant over the working range of temperatures. A high pressure pump 2, Fig. 3, hydraulic connecting post 3, reservoir 4 and differential piston and cylinder unit 5, Fig. 2, are all mounted on a base 1 having four adjusting screws 6 and a bubble level indicating gauge 7. The pump 2 is of the screw operated single stroke type, the screw being operated by a capstan handle 8 to generate hydraulic pressure, the base being steadied by an adjacent handle 9. The pump 2 is connected by a union 12 to the post 3 which is fed directly from the reservoir 4 under the control of a needle valve operated by a knob 13, a union 14 and pipe 15 connecting the post 3 to the piston and cylinder unit 5. The unit 5 comprises the body 16 with bore 17 in which the cylinders 18, 19 are secured in fluid-tight manner. Pistons 28, 29 slide in the cylinders 18, 19 and are interconnected by a wire 31 secured by collets 32, 33. The upper cylinder and piston 19, 29 have a larger diameter T and are made of a metal or alloy having a lower coefficient of expansion a 1 than the diameter B and coefficient a 2 of the lower cylinder and piston 18, 28 and the dimensions and coefficients are chosen so that T<SP>2</SP>/B<SP>2</SP>is approximately equal to a<SP>2</SP>/a<SP>2</SP> whereby the difference of effective areas of the piston and cylinder units will remain substantially constant with temperature changes over a working range. A pressure gauge to be tested is connected to a union 37 on the post 3, the valve 13 is opened while the handle 8 is unscrewed to fill the pump 2 with liquid from the reservoir, the valve 13 is then closed while the pump handle is screwed up until a weight pan 34, secured to the upper piston 29 and carrying a weight representing a certain pressure, is lifted off an abutment 36 in the bore 17 and rises to a position where it is entirely supported by liquid pressure as indicated by a level marked on an adjacent post 35. The pan 34 is rotated by its knurled edge to overcome friction and allow the correct pressure defined by the weight to be generated and applied to the gauge under test. Specification 596,043 is referred to.