Gas Pressure Training Tutorial

Introduction to Gas Pressures

• Derek introduces the tutorial on gas pressures, emphasizing the importance of understanding different types of pressures encountered during gas training.

• A change in terminology is noted: "working pressure" has been replaced with "operating pressure" at both the meter and appliance levels.

Equipment for Measuring Gas Pressure

• The tutorial will cover various tests using different equipment, including a U-gauge (water gauge) and digital manometers.

• Preparation steps for using a U-gauge are discussed, highlighting the need to level and zero it before use.

Understanding U-Gauges

• Explanation of how to read water levels in a U-gauge, focusing on the meniscus effect where water dips in a tube.

• Importance of keeping the U-gauge steady to avoid false readings; utilizing hooks for stability is recommended.

Conducting Tightness Tests

• Steps for performing a tightness test are outlined, starting with leveling and zeroing the manometer before connecting it to the meter.

• The first test conducted is a let-by test on the emergency control valve (ECV), typically performed between 7 and 10 millibars.

Analyzing Test Results

• After conducting the let-by test at eight millibars for one minute, permissible rises or drops are explained.

• If there’s no significant rise or fall during this period, further tests can proceed without concern about gas leaks.

Permissible Rises and Digital Manometers

• Discussion on permissible rises when using different gauges: 0.25 millibars for U-gauges versus 0.2 millibars for digital manometers.

• Emphasis on accuracy when using digital manometers; two decimal points provide better precision than one decimal point.

Final Testing Procedures

Temperature Stabilization and Tightness Testing

Overview of Temperature Stabilization

• The speaker discusses the process of temperature stabilization, emphasizing the importance of maintaining a pressure of 20 millibars during a two-minute tightness test.

• Key figures to remember include: 7-10 millibars for one minute, and 20-21 millibars for one minute during the tightness test.

Permissible Drops in Tightness Tests

• A drop in pressure is permissible as long as it remains within specified limits (e.g., four, eight, or one millibar), but zero drop is required on pipework regardless of its age.

• If a drop occurs during a tightness test, appliances must be isolated to confirm that the drop isn't from the pipework itself.

Understanding Pressure Drops with Appliances Connected

• When appliances are connected, permissible drops vary based on pipe size; for example:

• For pipes ≤28mm with an E6 gas meter: allowed an 8-millibar drop.

• For U6 or G4 meters: allowed a 4-millibar drop.

Further Details on Pipe Sizes and Pressure Drops

• For pipes >28mm but <35mm:

• E6 meter allows a 4-millibar drop,

• U6 or G4 allows a 2.5-millibar drop,

• U16 or G10 allows a 1-millibar drop.

Standing Pressure Measurement

Definition and Importance

• Standing pressure refers to gas pressure when it is not moving; it's crucial for confirming gas presence in the system.

Procedure for Measuring Standing Pressure

• The standing pressure should only be measured after purging has been successfully completed following a tightness test.

Acceptable Range for Standing Pressure

• Ideal standing pressure ranges between 19 and 30 millibars; below this indicates insufficient gas flow while above can lead to issues like water spurting from regulators.

Calculating Accurate Standing Pressure

Methodology

• To measure standing pressure accurately, slowly open the emergency control valve (ECV), allowing gas into the u-gauge.

• Read both legs of the u-gauge, add them together, then divide by two to find the accurate standing pressure.

Example Calculation

• An example shows if both legs read at 23 millibars each, adding them gives you 46; dividing by two confirms an accurate reading of standing pressure at 23 millibars.

Transitioning to Operating Pressure Measurements

Next Steps After Standing Pressure Measurement

Understanding Operating Pressure at the Meter

Importance of Operating Pressure

• The operating pressure at the meter should be 21 millibars, with an acceptable range of ±2 millibars (19 to 23 millibars).

• This pressure is determined based on a flow rate equivalent to 3.5 meters cubed per hour, which corresponds to approximately 33-34 kilowatts.

• A minimum flow rate of 0.5 meters cubed per hour (around 4 kilowatts) is also established for proper functioning.

Testing Appliances for Maximum Flow Rate

• When testing, all appliances should be set to maximum output except for cookers, which require testing on their three largest rings.

• It’s crucial that during tests, the system maintains a minimum pressure of 19 millibars without any faults like incorrect pipe sizing or inadequate incoming pressure.

Conducting Tightness Tests

• During tightness tests on cookers, ensure that the glass lid is up; this allows for proper checks on potential leaks from hobs.

• The three largest rings must be activated to accurately measure working pressure at the meter.

Measuring Working Pressure

• For the cooker tested with its three largest rings active, a working pressure reading of 22 millibars was recorded.