Patent GB-1341760-A (GB)
Title: Flow control apparatus
IPC: G05D16/20
Filed: 1971-04-19
Abstract: 1341760 Fluid-pressure servomotor systems WESTINGHOUSE ELECTRIC CORP 19 April 1971 [25 March 1970] 24191/71 Heading G3P [Also in Division A5] Apparatus for introducing a fluid into a system comprises: a flow control unit with an inlet connectable to a source of said fluid, and an outlet; a discharge orifice operatively connected with said control unit by a fluid passage; means for supplying said orifice with a fluid for discharging; a surface positioned adjacent said orifice, and a sensing device capable of sensing some parameter of the system and moving the surface relative to the orifice in response to the sensed parameter. The pressure of the surface adjacent the discharging orifice causes a back pressure in the fluid passage; this back pressure is used to activate the flow control device and admit fluid to the system at a rate which is a function of the magnitude of the back pressure. An embodiment for keeping constant the partial pressure of oxygen in a closed circuit breathing system is described. The electrical signal from a partial pressure of oxygen sensor 20 is fed via wires 83, 84 into a modified galvanometer 22, which is calibrated 87 to give a reading of the oxygen partial pressure. The armature of the meter is a disc 58 which is eccentrically mounted on an axle 63, 64. A discharge orifice 50 is mounted adjacent the peripheral surface 55 of the disc, defining a gap 56, the magnitude of which is, because of the eccentric mounting of the disc, a function of the output of the sensor 20. The flow control unit 10 has an inlet 12 leading to an inlet chamber 25 and an outlet 16 leading from an outlet chamber 28, the chambers 25 and 28 being joined by a passage 36 which is normally closed by a tilt valve 30. A passage 42 and tube 23 feed oxygen from the inlet to the discharge orifice 50, a flow restrictor 44 in the passage 42 limiting the amount of oxygen. If the surface 55 is sufficiently far away from the discharge orifice to cause negligible back pressure in the tube 23, then the pressure in the upper diaphragm chamber 39 is substantially the same as the system ambient pressure, that is equal to the pressure in the outlet chamber 28. Under these conditions the diaphragm will not move and the valve 30 remains closed. If however the surface 55 is close enough to the orifice to cause a back pressure, the pressure in the upper diaphragm chamber 39 will be greater than that in the outlet chamber 28 and the diaphragm will be urged downward, thus opening the valve 30 and admitting oxygen to the system. The smaller the gap 56 the greater will be the back pressure and the more the oxygen supply valve 30 will be opened. A valve 96 may be included in the tube 23 in order that the tube may be fully closed thus causing the maximum back pressure and thus fully opening the tilt valve 30. The invention is set up by placing in an atmosphere of known oxygen content and adjusting the position of the orifice 50 using the knob 93 until the back pressure is just insufficient to open the tilt valve. The apparatus will then maintain this value of oxygen partial pressure in any atmosphere in which it is placed, for if the oxygen content falls below this level the output of the sensor will cause the disc to rotate in a sense which narrows the gap 56 and more oxygen is admitted. The device can be made fail-safe by having the flow restrictor 44 of such a size that the amount of oxygen escaping from the orifice is sufficient to sustain life if the control mechanism fails.