Meriam's M201 is a special manometer that has been built specially for testing rotary gas meters used in commercial and industrial utilities. The M201 has special dampening circuitry to offset pulsation and provide an accurate differential reading.
The M201 has two hoses that need to be connected to two pressure points, one upstream of the meter and the other downstream. This is usually accomplished via two plugs installed in the taps located at the top of most rotary meters.
Once the test is performed and the current differential pressure is obtained, it is checked with the differential chart provided by the meter manufacturer for a given flow rate.
If the differential value is within range it is inferred that the meter is accurate. If the differential value is outside of the acceptable range, troubleshooting of the meter must begin that may involve disassembly or repair.
Since a rotary meter is a mechanical device there are of course a number of issues that can cause the differential/accuracy to be outside of specification. The most common issue falls into the category of increased internal resistance.
This can be associated with a bind in the rotors caused by improper installation, shock or debris. Debris could be large pieces, small pieces, or even an accumulation of pipe dust.
The meter may have either too much or not enough oil. Finally, another possible issue could be bearing wear or failure thus new bearings would be required. To minimise these common problems we suggest that rotary meters not be installed with heavy pipe strain, valves are always opened slowly to prevent shock, filters or strainers are always installed upstream of the meter, and that meters are properly maintained, particularly monitoring that the oil level is always half way up the sight glass.
It has been proven for several years now that the differential testing of rotary meters can be an effective supplementary or even primary field proving method.
These tests can in some instances be completed in just a few minutes and can save a utility considerable costs.
Using this proven testing method and test equipment on a more frequent basis than transfer proving can and will prove beneficial to any utility, large or small.
Meriam’s M201 has new features to make drop testing Rotary (Natural) Gas Meters even easier! New hardware options protect the M201from one-sided overpressure. Options include a 1/4 turn valve manifold and an integral push-to-read cartridge valve in addition to the traditional push-to-read valve manifold.
More importantly, new operating features provide users with a live pressure display and more automation to make field use easier than ever before.