Stepper motor valve and method of control

A fuel-fired heating system comprising:

• a burner for receiving a supply of fuel flow for combustion in a fuel-fired heating apparatus;
• a furnace control for communicating a requested fuel flow;
• a stepper-motor regulated gas valve control for supplying fuel flow to the burner;
• the stepper-motor regulated gas valve control including:
• an inlet, an outlet, and a flow path therebetween;
• a main diaphragm chamber;
• a main diaphragm in the main diaphragm chamber that controllably displaces a valve relative to a valve opening in response to changes in pressure in the main diaphragm chamber, to thereby permit adjustment of the flow of fuel through the valve opening;
• a servo-regulator diaphragm configured to selectively block fluid flow into the main diaphragm chamber to thereby control the rate of fuel flow through the valve opening, the servo-regulator diaphragm being fluidly disconnected from the outlet when the valve is closed;
• a stepper motor coupled to the servo-regulator diaphragm and configured to move in a stepwise manner to displace the servo-regulator diaphragm for regulating fluid flow to the main diaphragm chamber, to thereby regulate the rate of fuel flow through the valve opening;
• and
• a system controller coupled to the stepper motor and the furnace control, the system controller configured to receive an input control having a current between 0 and 180 milliamps from the furnace control, the input control signal indicative of the requested fuel flow through the valve, the system controller configured to control the movement of the stepper motor, based on the input control signal, to provide an opening characteristic of the valve that is a function of the valve's outlet pressure over time.

A method for controlling fluid flow through a stepper-motor gas valve of a heating system, the stepper-motor gas valve including a main diaphragm chamber, a main diaphragm coupled to a valve and configured to displace the valve relative to a valve opening in response to changes in pressure in the main diaphragm chamber, a servo-regulator diaphragm configured to regulate fluid flow to the main diaphragm chamber and to be fluidly disconnected from an outlet of the gas valve when the valve is closed, and a stepper motor coupled to the servo-regulator diaphragm, the method comprising:

• receiving an input control signal from a furnace control of the heating system, the input control signal having a current in the range between 0 and 180 milliamps, the input control signal indicative of a requested fluid flow;
• converting the input control signal to a reference value between 0 and 5 volts, the reference value representative of the input control signal;
• determining a motor step value based on the reference value and a type of the fluid source coupled to the valve;
• and
• based on the motor step value, causing the stepper motor to displace the servo-regulator diaphragm to selectively block fluid flow into the main diaphragm chamber, to thereby provide the requested fluid flow through the stepper-motor gas valve.