In our continuing series on natural gas flow meters, here I discuss another positive displacement meter, the rotary meter. While this meter was initially introduced to measure liquids, much of this post is dedicated to measuring natural gas. The rotary style meter excels in measuring high-volume applications for utility billing and submetering.
Natural Gas Flow Measurement
Our posts frequently share applications for thermal mass flow meters because that is our business at Sage Metering. Our thermal mass meters excel in a wide range of applications, but there are other meters that work well in other gas flow measurement areas. For this reason, this series introduces some other metering alternatives.
The rotary meter is often referred to as a rotary piston meter. The technology was initially introduced in 1846 by the Roots brothers in the water pump design. In 1920, the first, gas rotary meter was released using the lobed impeller model from the Roots brothers’ design. Over the years, there have been many improvements in materials, modular design, manufacturing and electronics.
PD Meters or Positive Displacement
The rotary meter is in a class of meters referred to as positive displacement, or PD meters. PD meters are recognized as having longtime technology, have a high degree of accuracy and remain the workhorses in the industry, even though other technologies have advanced. The PD meter requires fluid flow to physically or mechanically displace the components of the meter to measure the volume; therefore, it achieves volumetric flow.
These precision-machined meters contain two figure-8 shaped lobes which spin in correct alignment. With each rotation, they displace a precise quantity of the substance being measured. Another PD meter is the diaphragm meter, which also serves well in gas billing. Rotary meters, however are capable of handling higher volumes and pressures than the diaphragm meter.
The rotary meter is recognized for its accuracy and is used in utility billing and submetering. Over the years, as well-served diaphragm meters are being taken out of service, particularly the larger commercial and industrial sized meters, many are being replaced with a lighter and smaller rotary meter.
The meter has moving parts and limited to metering clean, dry gases. Since the meter measures volumetric flow, it also requires pressure and temperature compensation to obtain corrected gas flow.
Manufacturers of rotary meters for natural gas include Elster American (RPM), GE Measurement & Control Solutions (Dresser Roots), Itron (Delta), Romet Limited, and others.
If you are interested in natural gas flow measurement, you may want to review the following meter styles:
- Coriolis Flowmeter
- Diaphragm Meters
- Gas Turbine Meter
- Ultrasonic Flowmeters
- Orifice Plates
- Thermal Mass Flow Meters
Photo: Wikipedia (Rainer Bielefeld)