An appurtenance (also called an appendage) is any valve, tap, shut-off device, fitting or control component attached to a piping system to regulate, direct or isolate the flow of a fluid.
In building services, industrial installations and civil infrastructure, the term appurtenance covers a broad family of accessories that are essential for the operation and maintenance of pipe networks.
Common types of appurtenances
- Gate valves — used to fully open or fully close a pipeline; not suitable for throttling.
- Ball valves — quarter-turn valves offering quick shut-off; common in smaller-diameter domestic pipework.
- Butterfly valves — lightweight disc valves for larger-diameter lines, used in HVAC and water distribution.
- Check valves (non-return valves) — allow flow in one direction only, preventing backflow.
- Pressure-reducing valves — reduce incoming mains pressure to a safe working level.
- Taps and bibcocks — end-of-line draw-off points for water supply.
- Strainers and filters — protect downstream equipment by removing particles.
- Air release valves — expel trapped air from high points in a pressurised system.
- Expansion vessels — absorb pressure fluctuations caused by thermal expansion.
Why appurtenances matter
Without appurtenances a piping system would be a passive set of tubes with no means of control. They allow operators and maintenance engineers to:
- Isolate sections of a network for repair without shutting down the entire system.
- Regulate pressure and flow to match demand.
- Prevent contamination through backflow.
- Drain or vent the system safely.
Standards and specifications
Appurtenances must be selected to match the pipe material, diameter, pressure class and the medium being transported (potable water, gas, steam, chemicals). In Europe, product standards such as EN 1074 (valves for water supply) and EN 13828 (building valves) define performance and testing requirements.
Installation considerations
Valves and fittings should be installed at accessible locations to allow inspection and replacement. Many specifications require isolation valves at regular intervals and at the entry to each building zone or apartment.
Related terms
- Valve
- Piping system
- Backflow preventer
- Isolation valve