Vacuum
Pressure lower than atmospheric pressure.
Vacuum Activators
Dampers and control valves used in automotive air conditioning system; controlled by the vacuum created by engine intake manifold vacuum.
Vacuum control system
Intake manifold vacuum is used to operate dampers and controls in some automobile systems.
Vacuum Pump
Device used for creating vacuums for testing or drying purposes.
Valve
Device used for controlling fluid flow.
Valve, Expansion
Type of refrigerant control that maintains constant pressure in the low side of refrigerating mechanism. Valve is caused to operate by pressure in low or suction side. Often referred to as an automatic expansion valve, or AEV.
Valve, service
Device used to check pressures and charge refrigerating systems.
Valve, solenoid
Valve made to work by magnetic action through an electrically energized coil.
Valve, suction
Valve in refrigeration compressor that allows vaporized refrigerant to enter cylinder from suction line and prevents its return.
Valve, water
In most water cooling units, a valve that provides a flow of water to cool the system while it is running.
Valve plate
Part of the compressor located between the top of compressor body and the head. It contains compressor valves and ports.
Vapor
A gas that is often found in its liquid state while in use. The preferred name for vaporized refrigerant.
Vapor, saturated
Vapor condition that will result in condensation into droplets of liquid if temperature is reduced.
Vapor Barrier
Thin plastic or metal foil sheet used to prevent water vapor from penetrating insulating material.
Vaporization
Change of liquid into a gaseous state.
Vapor lock
Condition where liquid is trapped in a line because of a bend or improper installation. Such vapor prevents liquid flow.
Vapor pressure
Pressure imposed by a vapor.
Vapor pressure curve
Graphic presentation of various pressures produced by refrigerant under various temperatures.
Vapor recovery method
A refrigerant recovery system using relatively small equipment to remove refrigerant from residential, automobile, and light commercial units.
Vapor velocity
Speed or rate at which a gas moves.
Variable Air Volume (VAV) controller
Device having electronic components used to regulate the volume of air in a distribution system.
Variable control
A control that can make gradual adjustments to equipment, as opposed to-a simple onoff control.
Variable pitch pulley
Pulley that can be adjusted to provide different pulley drive ratios.
VAV
See Variable air volume.
V-belt
Belt commonly used in refrigeration work with a contact surface and pulley in a V-shape.
Velocimeter
Instrument used to measure air speeds.
Velocity
Quickness of motion; swiftness speed. Change in position with respect to time.
Ventilation
Airflow from one area to another.
Vibration absorbers
Soft or flexible substance or device that will reduce the transmission of a vibration.
Viscosity
Resistance to floe,.
Vmax
Maximum (peak) voltage in alternating current cycle.
Volatile
Easily vaporized; A liquid that changes to the gaseous state readily.
Voltage
1- Terrn used to indicate the electrical potential or electromotive force in an electrical circuit. 2-Voltage or electrical pressure which causes current to flow, 3-Electromotive force.
Voltmeter
Instrument for measuring, voltage in electrical circuit
Volumetric efficiency
Term used to express the relationship between the actual performance of a compressor or of a vacuum pump and theoretical performance of the pump based on its displacement.
Vortex tube
Mechanism for cooling or refrigerating that accomplishes cooling effect by releasing compressed air through a specially designed tube.
Vrms
Root mean square voltage; average voltage equal to the maximum voltage multiplied by a constant.