Rotary Gas Meters (Common CGR)
Rotary Gas Meters
Function of Common CGR Gas Meters
The gas flow through the rotary gas meter measurement chamber causes the two “8”-shaped rotors to turn. The volume of gas closed between the measuring chamber walls and rotors is transported four times in one full cycle from the meter inlet to the outlet. The timing gears set the rotors at the angle of 90° one to the other. The gear train, and the incorporated gas tight and hermetic magnetic coupling, transfers the rotor rotation to the index unit, which is separated in that way from the pressure tight housing.
The actual volume of gas is indicated on the mechanical counter. The measurement cartridge, as a separate unit, is fixed in the pressure resistant housing by means of elastomere gaskets. Thanks to this, the possible stresses, e.g. arising from improperly aligned piping, have no influence on measurement results of the CGR Rotary Gas Meter. Moreover, the measuring cartridge elements are made of materials with carefully selected values of thermal expansion coefficients. This minimizes temperature stresses that could cause the rotor seizures. All above factors, together with the highest precision machining of parts allow to reduce small but necessary clearances between the moving rotors and the measurement chamber walls, what reduces gas leakages to minimum and results in very high accuracy and wide measuring ranges of our CGR Rotary Gas Meters.
The CGR Rotary Gas Meter consists of the following main assemblies: Pressure resistant housing Measuring assembly Magnetic coupling Index head All parts subject to servicing or maintenance, like mechanical counter, LF (HF) sockets, oil filler and drain plugs, oil level sight-glass, are located on the front side of the meter. Thanks to this, it is not necessary to access the back side of the CGR meter and then it could be located very close to a wall or other construction element what reduces the installation deep.
ROTARY GAS METERS – MEASUREMENT OUTPUTS
Reference pressure (operating pressure) connection tap is located in the centre of the housing and is marked as “pr”. On the same side of the body there is another pressure tap for measuring the outlet pressure, if necessary. Same taps are also placed on the opposite side of the housing. For the measurement of the gas temperature, the gas meter can be optionally equipped with two temperature pockets located at the inlet side of the body. Same taps may be also placed on the opposite side of the housing.
The mechanical index unit indicates the actual volume of the measured gas at operating temperature and operating pressure. It can be rotated axially by 350° in order to facilitate the readings and enable easier connection of pulse sensor plugs. The index unit is provided with one low frequency LFK reed contact pulse transmitter, as a standard. On request the index may be equipped with: – LFI inductive pulse sensor (NAMUR) – HF inductive pulse sensor (NAMUR).
Installation & Recommendations
Installing Rotary Gas Meters
- Gas meters should be shipped in their original package to the place of installation.
- Gas meters have to be handled with care and be protected from falls, direct influence of rain, snow or high humidity.
- Rotary meters can be installed in horizontal or vertical position (index head may be rotated by 350°).
- The upstream pipe installation have to be equipped with a gas filter (10 micron accuracy is recommended). Before putting into operation new stations or installations, it is recommended to install a Top Hat filter or a temporary cone sieve strainer.
- To assure proper work of the lubricating system, the gas meter has to be installed in horizontal position, and any mechanical shocks during the installation are not permitted.
- It is recommended to install the meter in closed compartments, if possible. When installed outdoors a protection against direct weather influence should be used.
- The piping should be executed so as to avoid unnecessary stresses acting on the meter.
- When starting the gas flow through the installation, the valves should be opened slowly to avoid gas impingement which could damage the meter.