Patent GB-773523-A (GB)
Title: Improvements relating to engine indicators
Inventor: ROACH WALTER JAMES ROBINSON
IPC: G01L23/32
Filed: 1952-10-24
Abstract: 773,523. Engine indicators; recording-apparatus. DOBBIE McINNES, Ltd. Oct. 19, 1953 [Oct. 24, 1952], No. 26697/52. Classes 106(2) and 106 (4). An apparatus for recording curves of pressure variation throughout an engine cycle comprises a small-bore cylinder 50 and pointer 51, Fig. 1, for moving a first spark point 62 in response to high pressure variations; a large-bore cylinder 77 and piston 78, Fig. 5, for moving a second spark point 75 in response to low pressure variations without the necessity of movement-magnifying linkage; and record-carrying means 63, 76 with which the spark points co-operate to effect a record. A common record carrier for the two spark points 62, 75 may be used. To each cylinder head 10, 11, 12, Fig. 1, is coupled a pressure controlled contact breaker 13. This contact breaker, Fig. 2, includes a metallic diaphragm 17 acted on on one face by an adjustable fixed pressure applied through a filter and desicator unit 33; and on the other face by the varying pressure within the cylinder through a connection 20. When the pressure in the engine cylinder reaches that applied through 'the desicator unit 33, the diaphragm 17 contacts an electrode 22 in an insulating bush 24 to cause one or other of the spark points 62, 75 to operate and make a mark on the record sheet mounted on the associated revolving record carrier. The low-pressure piston 78, Fig. 5, is formed with a radial clearance, for example between one and two thousandths of an inch, and the piston 78 and rod 79 are guided by end plates 107. This reduces friction. Each piston is displaceable to and fro against spring action, the springs being adjustable or replaceable to enable indicator diagrams to be taken to different scales. The adjustable fixed pressure is applied to the low pressure piston 78 through a pipe 90 and thence through a pipe 91 to the contact breaker 13. The adjustable fixed pressure is applied to the high pressure cylinder 50 from a gas distribution box 44 that is also coupled to the contact breakers 13, there being screw-down valves for cutting off the lower pressure cylinder 77 when the high pressure cylinder 50 is being used and vice versa.  Adjustable fixed pressure. Air or an inert gas is blown under valve control 96, Fig. 8, through a nozzle 97 surrounded by a chamber 98 with apertures near the upstream side 99 and down stream side 100 of the nozzle 97, the chamber producing a partial vacuum at 99 when the down stream aperture is open to atmosphere, or a slowly increasing pressure at 99 as the downstream side 100 is slowly closed by a valve 101. Alternatively, the source of adjustable pressure may be a rotary pump 102 or a piston pump 103, the suction outlet 104 and the delivery outlets 105 of said pump being connected to a control valve 106 of piston-valve or change-over cock construction. The valve 106 has a third connection leading to the lowpressure cylinder 77 and it ensures that either the full suction or delivery pressure or any intermediate combination of the two may be available at the cylinder 77.