Gas valve control system for a water heater
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Solution Overview
Problem
Existing gas valve control systems in powered vent water heaters often confuse operators by indicating errors when the control system remains energized despite the gas valve being switched off, due to the large inductive fan load and the need for a master switch, which is costly and inefficient.
Innovation Solution
A double-pole double-throw (DPDT) manually-operated switch is used to supply power only to the gas valve coil, allowing the controller to sense the switch position using a low current DC voltage, and indicating its position to prevent errors and maintain operational state.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a master on/off switch is used to switch all power to the appliance off, then the gas valve is disconnected from electrical power, but the control system cannot sense the switch position and may indicate errors to the operator
Solution Approach 1:
The patent segments the power switching function into two separate circuits: a high-power circuit for the fan motor and a low-power circuit for the gas valve. The gas valve switch operates independently in the low-power circuit, allowing the controller to sense its position without being affected by the high inductive load of the fan motor. This segmentation resolves the contradiction by enabling reliable gas valve control while providing accurate switch position feedback to prevent operator confusion.
2Loss of information
If the control system remains energized when the gas valve is switched off, then the controller can detect the switch position, but the system may indicate errors when attempting to light-off the water heater
Solution Approach 1:
The patent implements feedback by having the controller continuously monitor the position of the gas valve switch through the low-power circuit. When the switch is in the off position, the controller receives feedback indicating this state and prevents light-off attempts, thereby eliminating error indications. The feedback mechanism allows the controller to make informed decisions based on the actual switch position, resolving the contradiction between maintaining system energization for detection and preventing erroneous error messages.
3Ease of manufacture
If a master switch is used to control all power to the appliance, then the assembly is simplified for the OEM, but a lighter duty switch cannot be used for the gas valve due to the large inductive fan load
Solution Approach 1:
The patent segments the electrical circuits into high-power and low-power portions, allowing the gas valve switch to operate independently in the low-power circuit. This segmentation enables the use of a lighter duty switch for the gas valve while maintaining the ability to control the high-power fan motor separately. The OEM benefits from simplified assembly through the modular switch design, while the device complexity is managed by clearly defining the boundaries between high and low-power circuit requirements.
Solution Approach 2:
The gas valve switch serves multiple functions: it controls the gas valve coil in the low-power circuit and provides position feedback to the controller. By designing the switch to handle only the low-power gas valve circuit, the system achieves universality where a single component (the switch) performs both control and sensing functions, simplifying the overall assembly while meeting the specific duty requirements for gas valve operation.
Data Source
AI summary
A system and method of operating a gas fuel valve control circuit are disclosed. The gas valve control circuit includes a gas valve assembly configured to control a flow of a fuel gas to a load and a switch assembly including a switch in each leg of a plurality of legs of a power supply to the gas valve assembly. The switch assembly is configured to supply power and a return to the gas valve assembly in a first position and to open the plurality of legs of the power supply to the gas valve assembly in a second position. The switch assembly is configured to indicate a position of the switch assembly.