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Murphy oil pressure gauges with switches that activate on low pressure. A pressure switch is a form of switch that operates an electrical contact when a certain set fluid pressure has been reached on its input. The switch may be designed to make contact either on pressure rise or on pressure fall.
After the control of air flow and temperature was standardized, the use of electromechanical relays in ladder logic to switch dampers became standardized. Eventually, the relays became electronic switches, as transistors eventually could handle greater current loads. By 1985, pneumatic controls could no longer compete with this new technology ...
Reversing valves are built into the heat pump by the manufacturer, and must be replaced by an HVAC technician if they fail. Since the valve is an integral part of the sealed refrigerant circuit, proper procedures for recovering and then later refilling the refrigerant must be followed, to prevent its loss into the atmosphere.
This damper can switch the electrical power to control additional "slave" dampers, minimizing the electrical load on the damper's control circuitry and power transformer A zone damper (also known as a Volume Control Damper or VCD ) is a specific type of damper used to control the flow of air in an HVAC heating or cooling system.
Pneumatically actuated shut down valve A diagram of the internal components of a safety shutoff valve. When this type of valve is tripped, the flow is quickly stopped and an indicator disc tells the operator that the electrical circuit has been opened by a failure somewhere in the system.
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Air coil freeze stat. A freeze stat is a temperature sensing device for HVAC that monitors a heat exchanger to prevent its coils from freezing.Freeze stats can be used on both refrigerant-to-air, and refrigerant-to-liquid type heat exchangers and serve different purposes with similar goals for each.
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