1. Principles of Valve Selection for Water Supply Piping
Selecting the right valve for a water supply line starts with defining the duty, not the price. Answer five questions first: (1) function - isolation, regulation, or backflow prevention; (2) size and pressure class of the line; (3) acceptable pressure loss - gate and butterfly valves add little resistance when open, globe valves add significant resistance; (4) flow direction - does the line carry flow in both directions; (5) installation space and how often the valve will be operated. These answers will eliminate most unsuitable valve types before you compare products.
2. Valve Selection Rules at a Glance
| Condition | Recommended Valve Type | Reason |
|---|---|---|
| Line size up to DN50 | Globe valve | Compact, good shut-off and regulation at small sizes |
| Line size above DN50 | Gate or butterfly valve | Lower pressure drop and cost for large lines |
| Flow or pressure regulation needed | Globe valve or regulating valve | Linear throttling capability |
| Minimum flow resistance (e.g., pump suction) | Gate valve (fully open) | Nearly unobstructed full bore |
| Bidirectional flow | Gate or butterfly valve | Globe valves seal in one direction only |
| Limited installation space | Butterfly or ball valve | Short face-to-face, light weight |
| Frequent operation | Globe or ball valve | Shorter stroke, less seat wear in cycling |
| Pump discharge / backflow risk | Check valve (with closing spring) | Prevents reverse flow and pump spin |
These rules reflect widely applied water-supply design practice (e.g., Chinese building water supply design practice per GB 50015, with similar guidance in EN 806 and the IPC). Confirm the applicable local code for the project.
3. Where to Install Isolation Valves
| Location | Purpose |
|---|---|
| Service entry from the mains | Isolate the building or zone from the network |
| Ring main nodes; long ring sections | Segment the network so sections can be shut down for repair |
| Branch line start points and household connections | Isolate individual branches or units |
| Risers (bottom; top and bottom of vertical loops) | Isolate floors or vertical zones; drain down |
| Pump suction and discharge | Maintenance isolation for pumps |
| Tank inlet, outlet and drain lines | Fill, drain and isolate storage tanks |
| Equipment supply lines (heaters, cooling towers) | Maintenance isolation for equipment |
| Sanitary fixture supply points | Local isolation for fixtures and appliances |
| Lowest point of the network | Drain valve for system draining |
Valves should be accessible for operation and maintenance, clearly labelled, and installed so that the stem can be operated without obstruction. Where pipe sections are too long, add segmenting valves so a leak does not drain the entire network.
4. Check Valves: Selection and Placement
Frequently Asked Questions
Should I use a gate valve or a globe valve on my water line? Use a gate valve (or butterfly valve) for isolation on lines above about DN50, where low pressure drop matters and the valve stays fully open or fully closed. Use a globe valve for regulation, frequent operation, or small lines (up to about DN50) where its higher resistance is acceptable.
Where should check valves be installed? On pump discharge lines, tank and tower outlet lines (where inlet and outlet share a pipe), and on the supply lines of closed heaters or pressurized equipment. They prevent reverse flow, backspin of pumps and contamination of the supply.
Why do I need air release valves? Air trapped at high points reduces effective flow area, causes noise, accelerates corrosion and can trigger pressure surges. Automatic air release valves at high points expel air during filling and admit air during draining, protecting the network from air binding and vacuum collapse.
Which code governs valve selection and placement? Practice varies by region: Chinese projects commonly follow GB 50015 (building water supply and drainage); European projects follow EN 806 and national plumbing codes; North American projects follow the IPC or UPC. Use the code applicable to the project's jurisdiction.
Why are globe valves not allowed on bidirectional lines? Globe valves are designed to seal in one direction only; with reverse flow the disc is not held onto the seat. Gate and butterfly valves seal symmetrically and are the correct choice where flow can reverse.
How do I prevent water hammer when closing valves? Close valves gradually rather than instantly, use slow-closing or damped check valves on pump discharge, avoid rapid pump starts/stops, and keep flow velocity within design limits (typically below about 2-3 m/s in water mains). Where surge analysis shows risk, add surge relief or air valves sized for the line.