Patent GB-190008755-A (GB)
Title: Apparatus for Measuring the Pressure on a Surface which Moves against a Fluid or against which a Fluid Moves.
Inventor: DARLINGTON PHILIP JACKSON
Filed: 1900-05-11
Granted: 1900-07-28
Abstract: 8755. Darlington, P. J. May 11. Pressure gauges; indicating direction of currents.- The apparatus is for determining the pressure on a surface of a fluid moving against it or against which it is moved, such as the pressure on a screw propeller at different points, on a ship's hull, or on the vanes of a turbine. The propeller blade 17 is recessed at the required points 1, 2, 3, Fig. 2, to receive diaphragms 22 and blocks 23, Fig. 5, which enclose air chambers 40 behind them. These air chambers are connected by passages 42, 42 and a tube 46 with the hollow 52 in the shaft 15, and thence by a tube 54 with an air reservoir 55 and air compressor 56, the former fitted with a pressure gauge 57. The blocks carry contacts 30, which are normally pressed against the contacts 38. From the contacts 38 wires 47, 48, 49 pass through the passages 42, 46 and hollow shaft, and are connected by a rotary switch b to the wires 4, 5, 6. Another rotary switch c is provided for a special test, to be described. Suppose, now, it is desired t determine the maximum pressure on the propeller at any of the points 1, 2, 3 during its rotation. Air is pumped into the apparatus by the compressor 56, until the diaphragm 22 is forced out sufficiently to keep the contacts 38, 30 out of contact. The switch 11 is then turned so as to connect the required pair of the leads 47, 48, 49 and 4, 5, 6 with the wire 12, and through the closed switch 13 with a current indicator m, line 14, and battery k to earth. Pressure is now gradually released by a valve 58, until a slight intermittent current is observed in the indicator m, showing that the contacts 30, 38 just touch at the moment of maximum pressure ; this pressure is then read off from the gauge 57. Minimum pressure is determined in a somewhat different manner. When it is desired to know the pressure on the blade at a certain definite point in its rotation, the switch 13 is opened, as shown in Fig. 1, and the switch c, which is adjustable, completes circuit at the required point in the rotation only, the test being made as before. The fitting a to connect the hollow in the rotating shaft with the fixed pipe 54 consists of a fixed ring surrounding the shaft and made airtight by stuffing-boxes. An annular chamber in the ring is connected to the tube 54, and a side port in the shaft opens into the annular chamber. The switches b, c are formed of insulated annular rings in contact with fixed brushes. In the case of the switch b the rings, which all rotate, are connected to the leads 47, 48, 49. In the case of the switch c, however, one ring rotates while the other is normally at rest. It can, however, be adjusted by a scale and pointer, according to the required angle at which contact is to be made. Electrical connection between the rings is established, during each rotation, by a stud projecting from the rotating ring striking a spring stud projecting from the adjustable ring. An aperture in the blade, normally closed by a plug, can be opened for blowing out moisture from the apparatus and so preventing the working parts from being frozen in cold weather. A coloured liquid may be forced out of this aperture for the purpose of observing the direction of the currents from the propeller blade.