Grain Systems PNEG-588-04 - Manual (Page 23)

6. Operation
PNEG-588-04 Deluxe Downwind Heater Installation and Operation 23
Modulating Valve Operation
1. The modulating valve regulates gas flow through the heater based on sensing unit in the plenum and
maintains a constant drying air temperature.
2. The sensing bulb of the modulating valve should be mounted through the bin wall with the side
reading “top” up. The bulb reacts to temperature. It changes the amount of gas (increase or
decrease), burning warmer or cooler depending on the position of the valve SET POINT. If the bulb
is cooler than it was at the SET POINT, the bulb senses the cooler temperature and opens the valve
further so more heat is applied to the drying air. If the bulb is warmer than it was at the SET POINT,
the valve closes further and reduces the temperature until the air is at the valve SET POINT.
3. It is important that the pressure regulator be set high enough to allow the modulating valve to deliver
enough gas to maintain the plenum temperature necessary. The regulator is normally factory set at
15 PSI (propane units). To set the regulator, run the heater and turn the modulating valve T-handle
in. This gets full line pressure to the burner. Then adjust regulator to read 15 PSI (depending on the
plenum temperature needed).
4. Turn the fan and heater ON. To set the modulating valve, turn the T-handle out (counterclockwise)
until loose and wait a few minutes for the plenum temperature to equalize. When the temperature
under the bin has equalized, gradually turn T-handle in (clockwise) about 1/2 turn at a time. Wait until
temperature under bin has equalized as before. If temperature under bin is less than the desired
temperature, continue turning T-handle in, increasing gas flow and waiting for plenum temperature
to equalize until the desired temperature is the stable temperature of the plenum. If temperature
under bin is the same 10 minutes after you last made any adjustments to the T-handle you can be
certain that the temperature under the bin is the SET POINT of the valve. 1 Turn of the T-handle
equals approximately 7°F of temperature.
5. The valve will now keep the plenum temperature at the set point regardless of ambient conditions as
long as humidistat or thermostat do not shut down the heater. A bypass orifice is used to maintain a
small flame when outside temperature is near or above the set point of the valve. The bypass insures
steady application of heat at minimum gas flow operation. By pass orifice will only operate correctly
if pressure regulator is set correctly.
6. To observe how the modulating valve increases the efficiency of bin drying, check the gas pressure
of the unit in the morning and compare to the pressure read mid-afternoon. If the ambient (outside)
temperature is significantly greater later in the day (as normal), the gas pressure will be less. Since
less heat is required to maintain the same temperature in the plenum, the modulating valve will have
reduced the amount of gas used by the heater.