A better way to calibrate chart recorders on natural gas pipelines

The Problem: The Challenges of Having to use Hydraulic Fluid in a gas pipeline

Todd has to calibrate multiple chart recorders on a gas pipeline but he has several concerns. Since it is a natural gas pipeline and it is the middle of winter, he is concerned about using hydraulic fluid to do the calibration. His concerns include:

  • Contamination: Because Todd has to use a liquid to calibrate a gas pipeline, there may be some residual fluid left over that that could create a false differential pressure
  • Damage to the chart recorder: Because is winter, this residual fluid in the sensing element could freeze and damage the chart recorder
  • Pressure Stability: Hydraulic fluid is less stable because it is incompressible and cannot expand to accommodate any fluctuations in volume

The Solution: A Ralston Instruments Calibration Manifold

A colleague told Todd about Ralston Instruments calibration manifolds. He is interested in this option because the manifolds use compressed nitrogen gas instead of hydraulic fluid. This feature helps to remedy Todd’s concerns because compressed nitrogen eliminates the risk of residual fluid contamination and will not freeze causing damage to the chart recorder. Moreover, unlike hydraulic fluid, compressed nitrogen is very stable because of its ability to expand to fill the test volume. Todd also likes that the Ralston Instruments calibration manifolds come complete with low volume hoses and quick-connect adapters that help to make setup easy and limits the amount of gas that is used with each calibration.

The New Configuration

Todd connects a quick-connect to the pressure regulator on his nitrogen bottle, one to the high side of the chart recorders and one on his pressure reference gauge. He uses the valves and fine adjustment control piston on the calibration manifold to dial in each of the test pressure points quickly and accurately. He is especially pleased that the calibration did not waste very much nitrogen since he was using the Ralston micro-bore hoses. He decides to use this calibration manifold from now on when doing static calibration of chart recorders and pressure transmitters.

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