Measuring the gas pressure

 

When they came to check the gas taps they used a manometer to test the pressure. A manometer is a U-tube. This is a U-shaped tube full of liquid. Normally the liquid level is the same on both sides because if it is disconnected, air pressures pushes down equally on the liquid surface on each side. To measure pressure, you leave one side open to the air and connect the other side up to a gas pipe. The pressure in the gas pipe should be higher than atmospheric and will push the liquid down on that side. By using the formula for pressure in the depth of a liquid (pressure = height of liquid x density of liquid x g) you can calculate how much higher the pressure is in the pipe than in the air.