Selection 

　　Valves serve the purpose of controlling the fluids in building services piping. Valves are produced in a variety of design types and materials.　　Proper selection is important to ensure the most efficient, cost-effective and long-lasting systems. 

Function 

　　Valves are designed to perform four principal functions:

　　1. Starting and stopping the flow

　　2. Regulating (throttling) the flow

　　3. Preventing reversal of the flow

　　4. Regulating or relieving the pressure of the flow

Service Considerations 

　　1. Pressure

　　2. Temperature

　　3. Type of fluid

　　　a) Liquid

　　　b) Gas; i.e., steam or air

　　　c) Dirty or abrasive (erosive)

　　　d) Corrosive

　　4. Flow

　　　a) On-off throttling

　　　b) Need to prevent flow reversal

　　　c) Concern for pressure drop

　　　d) Velocity

　　5. Operating conditions

　　　a) Condensation

　　　b) Frequency of operation

　　　c) Accessibility

　　　d) Overall size/space available

　　　e) Manual or automated control

　　　f) Need for bubble-tight shut-off