Category: Solenoids and Relays

Transformers for Low-Voltage Controls

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Transformers for Low-Voltage Controls

The use of low-voltage control systems is becoming more widespread as the demand for residential air conditioning increases. This necessitates the use of a transformer for voltage reduction, normally to 24 V. The selection of a transformer is not accomplished by merely selecting one that has the proper voltage requirements. The volt-ampere (VA) rating is …

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Hot-Gas Defrost Service Solenoid Valve

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Hot-Gas Defrost Service Solenoid Valve

Several piping arrangements are used for hotgas defrost systems, one of which is shown in Fig. 6-25. A portion of the compressor discharge gas is passed through the solenoid valve into the evaporator. The solenoid valve may be controlled either manually or automatically for this duty. Hot-gas defrost valve selection requires a slightly different approach …

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Suction-Line Service Solenoid Valve

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There are several applications, particularly on suction lines, where pressure drops in the range of 2 to 4 lb/in.2 (psi) cannot be tolerated. Therefore, only valves that are capable of opening at very low pressure drops are suitable for this type of use. Some valves incorporate the floating disc principle and are ideally suited for …

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Liquid-Line Service Solenoid Valve

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Liquid-Line Service Solenoid Valve

The primary purpose of a solenoid valve in a refrigerant liquid line is to prevent flow into the evaporator during the off cycle. On multiple systems, a solenoid valve may be used in each liquid line leading to the individual evaporators. The application of a liquid-line solenoid valve depends mainly on the method of wiring …

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Solenoid Valves Principles of Operation

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Solenoid valve operation is based on the theory of the electromagnets. The solenoid valve coil sets up a magnetic field when electrical current is flowing through it. If a magnetic metal, such as iron or steel, is introduced into the magnetic field, the pull of the field will raise the metal and center it in …

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HVAC Solenoid Valves

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HVAC Solenoid Valves

The primary purpose of an electrically operated solenoid valve is to control automatically the flow of fluids, liquid or gas. There are two basic types of solenoid valves. The most common is the normally closed (NC) type, in which the valve opens when the coil is energized and closes when the coil is de-energized. The …

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HVAC Power Relays

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HVAC Power Relays

A heavy-duty power relay that operates from solenoid action is shown in Fig. 6-20. In this device, a spring pulls the solenoid core, or armature, away from the electrical contact when the current is off. When current flows, the armature is pulled toward the coil. An electrical contact connected to the armature is either closed …

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HVAC Solenoid

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HVAC Solenoid

A magnetic field seeks the path of minimum reluctance, just as an electric current seeks the path of least resistance. Reluctance and resistance are related. Resistance refers to the opposition to current flow in a circuit. Reluctance refers to the opposition of the flow of a magnetic field. The lower the reluctance, the greater is …

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