Patent GB-683001-A (GB)
Title: Improvements in or relating to devices for bleeding off a part-flow of a gas in gas-metering systems
IPC: G01F15/04
Filed: 1950-09-07
Abstract: 683,001. Gas meters. GEHRE, H. Sept. 7, 1950 [Sept. 10, 1949], No. 22097/50. Class 54. In a gas metering system a part-flow is bled off to a meter 3, Fig. 2, by a constant volume chamber 1 operated by a meter 7 in the main-flow, the chamber 1 being repeatedly charged and the number of charges added to the meter 3 by a gear 31 having a ratio dependent on the volume of the chamber and by a summator device 32. The main-flow meter 7, Fig. 1, which may be either a Wottman, paddle or piston type, drives a camshaft 11 which operates the inlet and outlet valves 9, 10 of the chamber 1, the followers 18, 19 for these valves being loaded by the valve springs. The valve 9 is connected by a duct 4 to the entry side of the meter 7 while the valve 10 is connected by a duct 5 with a throttle 2 and the part-flow meter 3 which is fitted with a valve 8 controlling the pressure at which the point-flow escapes to atmosphere. The valve 8 and the throttle 2 may be omitted if the valve 10 is designed to act as a throttle and the barometric reading is taken as the exhaust pressure. The meter 3 is connected to one side 28 of a differential gear, the other side of which is driven by the camshaft 11 through a gear 25 and a pawl and ratchet mechanism 22, the planet wheel 29 of the differential gear being connected through the gear 31 with the summator 32. In order to avoid errors due to the mixing temperature in the chamber 1 differing from that of the main flow, the chamber is scavenged prior to each charge. This is accomplished by a valve 33, Fig, 3, which opens after the inlet valve and closes with it. The valve is operated by a cam 35 on a shaft 11 and controls a duct 34 leading to the exit side of the meter 7. If the latter is of the rotary displacement type the fall in pressure between the entry and exit sides tends to make the scavenging-gas volume considerable so that it is necessary to provide a lock between the chamber 1 and the exit side of the meter 7 and operated by the latter to hold the sweptout gas until the valve 33 has closed. One such lock comprises a chamber 50, Fig. 4, divided by a mass-loaded membrane 49 into lower and upper spaces 46, 48 connected by ducts 45, 47 with the duct 34, the duct 47 also being connected to the exit side of the meter 7. A slide valve 44 driven in timed sequence with the valves of the chamber 1 from the shaft 11 uncovers the duct 45 after the inlet and scavenge valves have opened so that gas flows into the space 46, raises the membrane 49 and causes a displacement of gas from the space 48 to the exit side of the meter 7. After the chamber 1 has been scavenged the valve 44 connects the ducts 45 and 47 together so that the membrane sinks to its original position displacing gas from the space 46 to the duct 47. The lock is then ready for another scavenging operation. In another construction of lock, the duct 34, Fig. 5, is connected through a one-way valve 58 to the top of a cylinder 53 and also to the centre of this cylinder which is connected by a duct 52 controlled by a valve 57 with the exit side of the meter 7. The valve 57 is operated from the camshaft I which is fitted with a pin 62 to engage a hook on the lower end of a rod 63 carrying two pistons 55, 56 suspended by a spring 54 from the top of the cylinder. In the upper position of the rod 63 the piston 56 separates the ducts 34 and 52. When the rod 63 is moved downwards by the pin 62 gas is drawn into the cylinder 53 until, shortly before the rod is released by the pin, the valve 57 is opened and the scavenging gas flows from the duct 34, across the cylinder 53 and into the duct 52. The return of the rod 63 to its upper position is retarded by the gas trapped above the piston 55. This gas escapes between the piston and cylinder. The valve 57 is closed and the piston 56 again separates the ducts 34 and 52. The chamber 1, the ducts 4, 5 and the scavenging device may be located in the gas to be measured to compensate for the temperature difference across the throttle 2 and to prevent heat exchange between the part-flow and the surrounding air.