Grain Systems PNEG-581 - Manual (Page 22)

22 PNEG-581 Deluxe Vane Axial Heater
5. Heater Operation
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. One (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. Bypass 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.