American Dryer Corp. AD-400 - Manual (Page 44)

Electric Butterfly Valve
The butterfly valve and its electric actuator cycle the gas burner from hi fire to low fire. The electric
actuator (EMA-418) operates on 115 volts single phase power and has a stroke of 90 degrees. When no
voltage is applied to the actuator, the valve is in the lo-fire position, and modulates to hi-fire position
when 115 volts is applied. Control power will not be applied to this actuator until the second motorized
gas valve has fully opened. This feature is controlled by an internal limit switch in the second gas valve.
Once Enabled this valve will now modulate from the lo-fire position to hi-fire. The gas burner flame will
always start at the lo-fire and then slowly increase to the hi-fire rate.
The lo-fire rate is set by adjusting the electric butterfly valve stroke arm to connecting linkage. When no
voltage is supplied to the electric actuator, the butterfly valve should be set to allow only enough gas to
the burner box to cause a small flame on all gas ports on the burner box floor. When the electric actuator
is pxjwered, the connecting linkage should be set so that the butterfly valve is at its maximum open
position. The hi-fire rate is set by a manual butterfly valve. The electric actuator's power supply is
controlled by the dryer's computer, not the burner controller module.
Manual Butterfly Valve
The manual butterfly valve sets the hi-fire gas rate of 1,600,000 Btuh. To achieve this rate, the differential
pressure between the gas inlet pressure and the burner box air pressure must be set for 22 inches water
column for natural gas and .9 inches water colunm for L.P. gas. To adjust, simply loosen the adjustment
dial screw and move the dial so that the proper pressure is obtained. Retighten screw.
Check Valve
At hi-fire, the gas pressure in the gas supply piping is higher than the air pressure in the burner box, and
the check valve will be closed and only raw gas is fed into the gas burner. When the electric butterfly
valve reduces the gas flow to cause lo-fire, the gas pressure in the gas supply pipe will be less than the air
pressure in the burner box. The check valve will now open, allowing some air to bleed into the lo-fire gas
supply. This gives a premix of gas and air which results in excellent flame stability at the lo-fire gas rate,
and it helps pressurize the gas inlet pipe so that gas flow is uniform at all gas ports. If the check valve disc
sticks closed, this will result in a yellow lo-fire flame.
2. Sequence of Operation
1. With dryer power on a 115-volt signal is sent to terminals 1 and 2 of the Burner Controller Module
(BCM). A power indicator light has been added to the controller base for troubleshooting purposes.
2. A diying cycle is started.'
3. Dryer computer calls for heat.
4. The BCM checks that all of the dryer's safety circuits are closed (terminal no. 7 of the BCM). If this is
the case, then the green "operating interlocks" LED on the BCM will light. If a safety switch is open,
the green LED will not light, and the red "system unsafe" LED will light. The ignition sequence will
stop.
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