Low fire start control
A direct gas-fired industrial air heater low fire start control, includes circuitry for simulating a resistant circuit which bypasses the discharge temperature sensors, the remote temperature selector, and a space temperature controls, that has the effect of driving the modulating valve to a fixed open setting which in turn changes the valve voltage in order to obtain desired gas flow. In a further embodiment, an isolated DC voltage source which normally bypasses the voltage input to the system of the modulating valve can be inserted into the circuitry to effectively drive the modulating valve to a fixed open setting to obtain the desired gas flow rate. Various circuitry, and bypass gas flow arrangements, are further shown to increase the efficiency of ignition of the burner assembly, when started.
1. A control system for a direct fire gas burner comprising:
a modulating valve for controlling gas output to the burner;
a control in electrical communication with the burner and with said modulating valve;
said control providing a low fire start gas condition of the burner above a minimum firing rate as said control interrupts electrical power to said modulating valve therein adjusting the flow of gas attaining a low fire start;
one of a space temperature selector in electrical communication with said valve and said control and a discharge temperature sensor in electrical communication with said valve and said control; and,
a simulated resistance circuit within said control capable of driving the modulating valve to an open setting in response to a resistance setting; the simulated resistance circuit comprising:
a first bypass circuit which bypasses said space temperature selector, said first bypass circuit including contacts to selectively open and close said first bypass circuit; and,
a second bypass circuit which bypasses said discharge temperature sensor; said second bypass circuit including contacts to selectively open and close said second bypass circuit.
2. The control system of claim 1 and further comprising:
said simulated resistance circuit bypassing the discharge temperature sensor and the space temperature selector, and driving the modulating valve to an open setting in response to a resistance setting.
3. The control system of claim 1 wherein at least one of said first bypass circuit and said second bypass circuit includes a resistor.
4. The control system of claim 3 wherein both said first bypass circuit and said second bypass circuit include a resistor.
5. The control system of claim 3 wherein said resistor is a variable resistor.