Valves, Controls, and Specialty Devices in Water Supply

Valves, Controls, and Specialty Devices in Water Supply

Every potable water system depends on valves and controls to isolate sections for repair, regulate pressure, prevent contamination, and accommodate thermal expansion. Selecting the wrong valve type — or installing a correct valve in the wrong orientation — can cause service failures, code violations, or health hazards. This lesson covers the seven devices you will encounter most often on the job.

Ball Valves

A ball valve uses a drilled sphere (the ball) that rotates 90° between fully open and fully closed. When the handle is parallel to the pipe, flow passes through the bore; when perpendicular, the bore is blocked. Full-port ball valves have a bore matching the pipe inside diameter, producing minimal pressure drop. Ball valves are the preferred isolation valve in modern potable systems because they close quickly, hold a tight shut-off, and are easy to inspect by handle position. They are not throttling valves — use them either fully open or fully closed.

Gate Valves

A gate valve lifts a wedge-shaped disc (the gate) out of the flow path when opened. It requires multiple turns to open or close fully. Gate valves cause very little pressure drop when fully open, but they are poor throttlers: partial opening causes vibration and accelerated wear. They are still found in older systems and on larger mains. Avoid installing them where frequent operation is expected.

Globe Valves

A globe valve passes water through an S-shaped path across a circular seat. A disc or plug screws down onto that seat to stop flow. This design provides fine flow control, making globe valves appropriate for throttling applications such as balancing lines. The tortuous flow path creates significant pressure drop, so they are not used as isolation valves on main supply lines.

Check Valves

A check valve allows flow in one direction only, closing automatically when flow reverses or stops. The body is stamped or cast with a directional arrow — always align this arrow with the direction of normal flow. Swing check valves use a hinged disc; spring-loaded check valves use a spring-biased disc. Orientation matters: swing checks must be installed horizontally or with flow moving upward; installing one with flow moving downward can cause the disc to slam open and never reseat. Spring-loaded checks can work in any orientation. Check valves are required by code on the cold-water inlet to water heaters in closed systems and at cross-connection control points.

Pressure-Reducing Valves (PRVs)

A PRV — also called a pressure regulator — automatically reduces high inlet pressure to a lower, steady outlet pressure. Inside, a spring-loaded diaphragm senses downstream pressure and modulates a seat to maintain the set point. Most residential and light-commercial PRVs are set to deliver between 50 and 80 psi downstream. Install a PRV with the flow arrow pointing in the correct direction, a strainer on the inlet side, and isolation valves and a gauge on each side for future service. Some PRV designs are orientation-sensitive; consult the manufacturer's instructions.

Expansion Tanks

When a water heater is connected to a closed system — one that has a backflow preventer or PRV on the supply — there is nowhere for the water to expand as it heats. Without relief, thermal expansion drives pressure above the relief valve setting repeatedly, shortening equipment life. A pre-charged expansion tank (a small steel vessel with an internal bladder) absorbs that expanded volume. The tank is installed on the cold-water supply line near the water heater. The air pre-charge in the tank must be set to match the static supply pressure before installation.

Hose-Bib Vacuum Breakers

A hose-bib vacuum breaker (HBVB) is a backflow prevention device threaded onto the outlet of an outdoor hose bib or laundry connection. It contains a spring-loaded check that opens to admit air when a downstream siphon forms, breaking the vacuum and preventing contaminated water from being drawn back into the potable supply. HBVBs are required by plumbing codes at all non-potable hose connections. They must be installed with the cap vents facing down so that the air ports are not submerged.

Thread Sealants for Potable Service

Only thread sealants listed for potable water use may be applied to fittings carrying drinking water. PTFE (polytetrafluoroethylene) tape and NSF-rated pipe dope (pipe thread compound) are the two standard choices. Apply sealant starting on the second thread from the end — leaving the first thread bare — to prevent sealant from entering the water stream. Never apply sealant to the female threads that seat against the valve disc; excess sealant at the seat can prevent full shut-off.

Installation and Safety Practice

Before working on any existing system, follow lockout/tagout (LOTO) procedures: shut the isolation valve, lock and tag it, and verify zero pressure with a gauge before breaking a joint. Wear safety glasses whenever cutting, threading, or pressure-testing pipe — chips and water under pressure are eye hazards. When tightening threaded valves, apply steady wrench pressure and stop when snug-plus-one-quarter to one-half turn; over-tightening cracks cast bodies and damages seats. Always confirm flow direction by reading the arrow cast or stamped on the valve body before final make-up.

Code Reference

Both the International Plumbing Code (IPC) and the Uniform Plumbing Code (UPC) contain provisions for valve types, locations, and backflow prevention. Your instructor will point out the specific sections applicable to your jurisdiction. When in doubt, check the adopted code and the manufacturer's installation instructions — both govern.