Airstream 18 owner manual Modulating Valve Operation

LTD HEATER OPERATION

MODULATING VALVE OPERATION

Your LTD heater is equipped with a modulating valve. The following material should be read thor- oughly.

1.The modulating valve regulates gas flow through heater based on sensing unit in the plenum, and maintains a constant drying air temperature.

2.The sensing bulb of the modu- lating valve should be mounted through the bin wall with the reading side top up. The bulb reacts to temperature. It changes the amount of gas (in crease 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 tempera- ture 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 re duces 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 neces- sary. The regulator is normally factory set at 15 psi. 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 regula- tor 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 min- utes for the plenum temperature to equalize. When the tempera- ture under the bin has equalized, gradually turn T-handle in (clock wise) about 1/2 turn. Wait until temperature under bin has equalized as before. If tempera- ture 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 ple- num. 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 de- grees F of temperature.

5.The valve will now keep the ple- num temperature at the set point regardless of ambient condi-

tions 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.

6.The modulating valve may re- quire minor adjustment periodi- cally if a certain temperature rise over ambient (outside) tempera- ture is desired.

7.To observe how the modulating valve increases the efficiency of bin drying, check the gas pres- sure of the unit in the morning and compare to the pressure read mid-afternoon. If the ambi- ent (outside) temperature is sig- nificantly 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 re- duced the amount of gas used by the heater. This is preferred to cycling the application of heat as is commonly done. The grain is not shocked and cooled quickly and then reheated, which is a waste of fuel in con- ventional bin drying systems.

17