Patent GB-852442-A (GB)
Title: Improvements in or relating to pressure-indicating instruments
IPC: G01L7/18
Filed: 1958-10-17
Abstract: 852,442. Pressure indicating apparatus. KALLE, K. T. Oct. 17, 1958 [Oct. 20, 1957], No. 33238/58. Class 106 (2). Apparatus for indicating small differences in pressures comprises two communicating containers 6, 14 holding liquid and connected at 2, 16 respectively to sources of gases the pressures of which are to be compared, rotor 8, 9 for maintaining a constant liquid level in the container 6, a smaller vessel 21 located in the container 14 having an inlet slot 24 and suspended on a bourdon tube 19, and a pump 13 driven at constant speed and having its outlet 25 connected to the bourdon tube which thus raises and lowers the vessel 21 depending on the proportion of gas and liquid drawn in by the pump from the vessel 21. The rotor 8 causes the liquid, which may be oil, in a surrounding container 1 to pass through a filter 5, be drawn through an opening 10 and fed through a hole 11 into the container 6 from which it overflows into the container 1. One gear-wheel of the gear pump 13 is connected to and drives the rotor shaft 8. The container 14 communicates with a chamber 15 surrounding it through an axial slot 17 and with the container 6 by openings 18 through which liquid enters and rises to a level determined by the pressure difference between the container 1 and the chamber 15. A rod 20 secured to the free end of the bourdon tube 19 extends through the slot 17 and loosely suspends the vessel 21 from a collar. The vessel 21 is slidably mounted over a pipe 22 connected to the suction side of the pump 13 and has an axial slot 24 the bottom end of which is located at approximately the level of the liquid in the container 14. The pressure side of the pump has a restricted outlet 25 and conduits 30, 31 connected to the bourdon tube 19 and a pressureindicating instrument, such as a manometer 32, respectively. The pump 13 withdraws a mixture of gas and liquid from the vessel 21 to which liquid is supplied through the slot 24. An over pressure, which depends on the proportion of liquid in the mixture withdrawn, is established at the pressure side of the pump due to the restricted outlet 25 and this causes the bourdon tube 19 to hold the vessel 21 so that the lower edge of the slot 24 is at or slightly below the liquid level in the container 14 to increase the proportion of gas supplied to maintain the moderate overpressure. If the pressure in the chamber 15 is lower than that in the container 1 the liquid level in the container 14 rises so that more liquid is supplied to the pump. The bourdon tube 19 straightens a little due to the increased pressure and the vessel 21 is raised so that a new equilibrium is established. The mixture discharged from the pump separates in a tube 27. The manometer 32 may be graduated to give a direct reading of the pressure difference between the container 1 and the chamber 15. The range of operation of the apparatus may be changed by screwing the container 6 upwards or downwards over a cylinder 3 to raise or lower respectively the liquid level. The apparatus may be used for purposes of regulation e.g. of the sub-pressure in a furnace by connecting the conduit 31 to a regulator.