Patent GB-591274-A (GB)
Title: Improvements in or relating to devices for indicating differences in pressure or liquid level
IPC: G01L7/22
Filed: 1944-06-27
Abstract: 591,274. Indicating-apparatus ; pressure gauges. DEHN, F. B. (Yarnall-Waring Co.). June 27, 1944, No. 12208. [Classes 106 (ii) and 106 (iv)] A device for indicating differences in pressure or liquid level, which includes magnetic means co-operating with a spiralled armature mounted to rotate about its longitudinal axis, the magnetic means being movable in response to differences to be indicated and causing the armature to rotate and perform an indicator movement is characterised in that the spiral is mounted for rotation in a non-magnetic well mounted in a wall and disposed at one side thereof, and the magnetic means are disposed on circumferentially opposite sides of the well and movable generally along its length. Thus, the spiral rotates an extent determined by its pitch and transmits indicator movement through the well. A pressure gauge, Fig. 1, comprises a casing 15 and a housing 16 held together by bolts 17 and sealed b annular packing 18, 19 lying on opposite sides of a diaphragm support 20 apertured at 21. The cover 16 is made concave at 31 to accommodate a diaphragm 27 held at its outer end by packing 19 and a support member 20. At its centre the diaphragm is stiffened and supported to move as a unit by plates 29, 30. which are fastened together and held by clamp members 32, 33 threaded together. The clamp member 32 is apertured at 35 for the passage of a pin 36, the end 38 of which bears on the inside of member 33. At the other end the pin 36 is pointed at 42 to form a pin bearing with a concavity 43 in a thimble 44 which engages with a spring 45 as shown at 46. The diaphragm 27 is subjected to different pressures on both sides, a standard pressure from pipe 39 to the right and a variable pressure from pipe 40 to the left. Axle pin 36 carries a collar 41 to prevent accidental withdrawal from the clamping members 32, 33. The spring 46 carries at its lower end a magnet 48 held by bolts 49 which also fasten a plate 50 attached to the thimble 44 to the magnet. The spring 45 is supported at its top end between a block 77 and its cap 78, both held to the housing 15 by bolts 79. The amount of retarding force which the spring offers to the diaphragm is controlled in two ways : (a) the fulcrum of the spring 45 is adjustable ; (b) the spring is shaped to offer different retarding forces for different positions of the fulcrum. The fulcrum is in the form of a bar 86 having a knife edge 87 extending across the spring. The bar 86 is movable down the length of the spring by means of screw 94 to which it is attached. The block carrying the knife edge fulcrum is slotted at 88 from the back 89 so as to permit the block to be moved normal to the spring, thus controlling its "zero setting." The spring is shaped as shown in Fig. 3, tapering at edges 84, 85, having a tapered-edged slot 80 and getting slightly thicker along its length from top to bottom. As the fulcrum moves downward, the retarding force of the spring increases. Between the poles of the magnet 48 there is situated a well 54 screwed to the casing 15 as shown in Fig. 1. Inside the well 54 there is a spiral armature 55 which, as the magnet 48 moves along the well 54 in response to variation in pressure difference, turns to maintain the initial " flux relationship " existing between the magnet and the spiral. Rigid with the armature there is a shaft 71 carrying a pointer 72 which moves over a scale indicating the amount of turning of the armature, i.e. indicating the pressure difference. If the difference of pressures on the two sides of diaphragm 27 does not vary according to a straight line law, the pitch of the spiral armature can be varied to provide compensation and so the scale over which the pointer 72 moves may be graduated uniformly. A sylphon bellows may be used instead of the diaphragm 27 and the spring 45 may be strengthened by supplemental springs if required. In another embodiinent, Fig. 4, a casing 112 is provided with two parallel compartments 115, 116 adapted to hold a pool 117 of mercury. A magnet 48<1> rests on the mercury in the compartment 115. A variable pressure is introduced into compartment 115 and a standard pressure or a higher variable pressure is admitted into compartment 116. There is a well 54, between the poles of the magnet 48<1>, in which a spiral armature 55 rotates to turn a pointer 72 as before to give an indication of pressure difference in the two compartments. In Fig. 6, the invention is applied to any plain float with a bailer or other chamber. The float follows the level 129 of liquid 130 and swings a magnet 48<2> attached by means of an arm 131 to the float. The magnet rotates an armature, located in a well situated between the poles, as before. The well is screwed on to a flanged member 133 secured to the side of casing 137 by bolts 136. The pointer 72<1> moves over a transparent scale 139 lit by lamp 140. The invention may be applied to measuring the pressure in a steam drum or measuring pressures on opposite sides of an orifice and so obtaining the " flow " through the orifice or the flow through a weir meter. In one embodiment, Fig. 11 (not shown), an electromagnet is used. A recording pen may be used instead of a pointer in any of the embodiments. Specification 308,321, [Class 106 (iv)], is referred to.