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VENTURI |
THROAT |
SERVICE |
PORT |
VENTURI |
INLET |
SERVICE |
PORT |
GAS VALVE |
SERVICE |
PORT |
Figure 32. Venturi Flow System Components.
combined in the throat and mix thoroughly as they proceed through the venturi tailpipe to the burner.
Service ports are provided at three places. On the right side of the venturi an inlet service port is provided just above the air filter box. Also on the right side, a throat service port is provided - at the narrowest section of the venturi casting. A gas pressure port is provided on the outlet face (right side) of the gas valve.
To evaluate system operation requires accurate measurement at these ports. A digital manometer, known to be accurately calibrated, is ideal. Other instruments may be used, but the “positive/negative” nature of the readings must be very clear. Also, gas pressure offset measurements are at very low levels (0.2” WC) and the instrumentation must be capable of determining it accurately.
4F-2. Venturi System Checkout
4F-2a. Unfired Venturi Differential Pressure
Before firing the unit, determine if air flow through the system is normal by operating the system with the gas valve turned off. Connect the positive side of the manometer to the venturi inlet port, which is at the bottom on the right side. Connect the negative side of the manometer to the outlet pressure port of the gas valve. (See Figure 33). Turn the gas valve knob to "Off". Turn the heater on by selecting "Pool" or "Spa" at the Flex Temp control and adjusting the temperature setting high. The blower will start immediately and the manometer will indicate the "unfired venturi differential" pressure. This is the pressure difference created by airflow through the venturi. It should be approximately 4.7" ± 0.3" at sea level. (See Section
If the reading is normal, proceed to gas pressure
offset measurement per the following section. If not, investigate air flow per section
Note that when the heater is operated with the gas valve off, it will eventually "lock out" because the ignition control does not sense flame. Normally, there will be enough time to obtain the measurement.
4F-2b. Gas Pressure Offset
Note that an equalizer tube is connected from a port on the front of the venturi inlet to the vent of the gas valve regulator. This is a very important component which allows the regulator to track air pressure even when abnormal things occur, such as blockage of the combustion air. Before firing, confirm that this tube and the venturi pressure switch tubes are in place and firmly connected.
Turn the heater off at the Flex Temp control. Turn the gas valve knob back to "On". With the manometer connections remaining as they were (See Figure 34) , start the heater at the Flex Temp control. When the burner fires, the manometer should read 0.2”
±0.1” WC — i.e., gas pressure is 0.2" WC less than venturi inlet pressure. If the offset is incorrect, adjust the gas pressure regulator to the correct pressure. This can usually be done while the heater is firing, but the burner may go off when the regulator seal cap is removed. In any case, the offset pressure measurement must be read when the heater is operating and the seal cap is firmly in place. Note that a special tool is required to remove the regulator cap.
Figure 36 shows the gas pressure offset reading when a
WARNING
In order to discourage incorrect adjustment by unqualified persons, the gas valve regulator cap requires a special tool for removal. Contact your Teledyne Laars representative about a special tool for this cap.
4F-2c. Gas Orifice Differential
Turn off the heater, disconnect the manometer tubes and replace the plug at the venturi inlet. Reconnect the tubes with the positive side of the manometer connected to the gas valve outlet and the negative side to the venturi throat as shown in Figure 35.
Turn on the heater. The manometer will read zero until the gas valve opens. Thereafter it should read 4.0”
±0.3 ” WC. See the sections on Air Flow Investigation and High Elevation Operation if this is not the case.
