Mechanical gauges measuring test pressures should have a scale that is not exceeding what factor of the test pressure?

In the context of the National Fuel Gas Code, mechanical gauges used for measuring test pressures need to be appropriately rated to ensure accurate and safe readings. The general guideline is that the scale of the gauge should not exceed five times the maximum test pressure that it will measure. This requirement is established to enhance the reliability of the gauge and to prevent any risk of damage or inaccurate readings that might occur if the gauge is undersized for the application.

When a gauge's scale is rated at a maximum of five times the test pressure, it allows for adequate resolution and safety margin. This setup ensures that the gauge operates well within its operational limits while providing precise readings during pressure testing. If the gauge were to have a scale that exceeds this recommended factor, it might result in reduced accuracy and increased uncertainty in pressure assessments, ultimately undermining system safety and integrity. Thus, a gauge with a scale not exceeding five times ensures that it is suitable for the intended pressure testing applications in a safe and controlled manner.