1

HVACR115 – Mechanical for Gas Heat

HVACR115 – Mechanical for Gas Heat

Measuring Gas PressureMeasuring Gas Pressure

2

Measuring Gas PressureMeasuring Gas Pressure

• To measure gas pressure in the manifold you use the tap in the manifold or the gas valve outlet.

• Tubing can also be slipped over one of the burner orifice hoods.

• Two devices are commonly used to measure gas pressures…

• To measure gas pressure in the manifold you use the tap in the manifold or the gas valve outlet.

• Tubing can also be slipped over one of the burner orifice hoods.

• Two devices are commonly used to measure gas pressures…

3

Spring GaugesSpring Gauges

• Bourdon tube gauges are the most common type of spring gauges.

• They have a hollow metal tube that is formed in a curve or arc.

• A pointer is connected to the closed end of the tube by means of levers.

• When pressure is applied through the open end of the tube it tends to straighten out.

• Bourdon tube gauges are the most common type of spring gauges.

• They have a hollow metal tube that is formed in a curve or arc.

• A pointer is connected to the closed end of the tube by means of levers.

• When pressure is applied through the open end of the tube it tends to straighten out.

4

Spring GaugesSpring Gauges

• As it straightens out it moves the pointer along a round dial and shows the pressure reading.

• Spring gauges are subject to mechanical damage and must be handled with care. They must also be checked for accuracy on occasion.

• As it straightens out it moves the pointer along a round dial and shows the pressure reading.

• Spring gauges are subject to mechanical damage and must be handled with care. They must also be checked for accuracy on occasion.

5

Spring GaugesSpring Gauges

• The pressure gauge is connected to the manifold or the control.

• And the pressure is then indicated directly on the dial.

• Depending on the pressure gauge the reading may be expressed in PSI or in inches of Water Column.

• The pressure gauge is connected to the manifold or the control.

• And the pressure is then indicated directly on the dial.

• Depending on the pressure gauge the reading may be expressed in PSI or in inches of Water Column.

6

U-Tube ManometersU-Tube Manometers

• Gas pressure is displayed in inches of water column on the manometer.

• A manometer is simply a U shaped tube made up of a transparent material.

• Both legs of the tube are filled about half way with tap water.

• The water level in the manometer with both ends open the atmosphere is the 0 level.

• Gas pressure is displayed in inches of water column on the manometer.

• A manometer is simply a U shaped tube made up of a transparent material.

• Both legs of the tube are filled about half way with tap water.

• The water level in the manometer with both ends open the atmosphere is the 0 level.

7

U-Tube ManometersU-Tube Manometers

• The tubing from the gas manifold or control is connected to one end of the U-Tube and the other end is left open to the room air.

• When gas pressure is applied to the manometer the water in the gas side of the tube is pushed down while the water in the other side rises.

• The tubing from the gas manifold or control is connected to one end of the U-Tube and the other end is left open to the room air.

• When gas pressure is applied to the manometer the water in the gas side of the tube is pushed down while the water in the other side rises.

8

U-Tube ManometerU-Tube Manometer

• The manometer then indicates the gas pressure in inches of water column.

• The height of the water column that the gas pressure will support with atmospheric pressure on top of the water column.

• Usually the U-Tube has a ruler in inches between the two tubes for easy measurement.

• The manometer then indicates the gas pressure in inches of water column.

• The height of the water column that the gas pressure will support with atmospheric pressure on top of the water column.

• Usually the U-Tube has a ruler in inches between the two tubes for easy measurement.

9

U-Tube ManometersU-Tube Manometers

• The scale readings extend both above and below a zero point.

• The pressure reading is obtained by adding the height of the water column above the zero point, the the distance BELOW the zero point.

• The scale readings extend both above and below a zero point.

• The pressure reading is obtained by adding the height of the water column above the zero point, the the distance BELOW the zero point.

10

U-Tube ManometersU-Tube Manometers

• You must initially line up the water level in the two legs of the manometer with zero on the scale with both ends open to the atmosphere.

• You must initially line up the water level in the two legs of the manometer with zero on the scale with both ends open to the atmosphere.

11

Gauge and electronic manometersGauge and electronic manometers

• There are newer manometers that are electronic or gauges. These are replacing the U-Tubes on most service trucks.

• Studies have shown that if taken care of properly these will serve the same purpose. However, the U-Tube is still the most accurate.

• There are newer manometers that are electronic or gauges. These are replacing the U-Tubes on most service trucks.

• Studies have shown that if taken care of properly these will serve the same purpose. However, the U-Tube is still the most accurate.

12

U-Tube ManometerU-Tube Manometer

13

Gauge SetGauge Set