Homes use a few main types of water valves. Ball and gate valves shut water off, globe valves can throttle it, and fixture stops shut off single fixtures. Check valves and backflow preventers keep water moving one way, a pressure-reducing valve lowers high pressure, and a water heater relief valve releases excess heat and pressure.
Which valves shut the water off?
These are the valves you actually touch. Their job is to stop water to the whole house, a branch, or a single fixture.
### Ball valves
A ball valve has a lever or short handle that moves only a quarter turn between open and closed, rotating a ball inside the body. The San Francisco Public Utilities Commission describes a main shutoff that is a ball valve with a handle "that turns off at a 90 degree angle to the supply pipe." That makes it easy to see whether it's open or closed.
Ball valves are on-off valves. NIBCO says ball valves "are generally not recommended for modulating service where critical flow rates are required." It also cautions against throttling any ball valve that is less than 45 degrees open.
### Gate valves
A gate valve has a round handwheel that takes several turns. NIBCO's gate valve instructions explain that flow "is stopped by forcing the wedge down between the seats of the body." On its non-rising stem design, turning the handwheel clockwise closes the wedge. SFPUC's advice for an older-style gate valve matches: "turn the wheel or handle on the valve clockwise until it stops."
Gate valves are strictly fully open or fully closed. NIBCO says they "should never be used for throttling purposes." For a closer comparison, see the difference between a ball valve and a gate valve.
### Fixture stops
These are the small valves under sinks, behind toilets and at the washer. They let you shut off one fixture without shutting off the house. Some are multi-turn, with a round or oval handle. Others are quarter-turn. BrassCraft says its quarter-turn stops control water flow "at the fixture or appliance with an easy 90-degree turn of the handle." They come in angle or straight styles for several pipe types, including CPVC and PEX.
Phoenix's adopted plumbing code requires them in most places. It calls for a shutoff valve on the supply to each plumbing fixture. In one- and two-family homes, bathtubs and showers are the exception. The code also wants one on the supply to each sill cock and to each appliance or piece of mechanical equipment. See how to shut off water to a fixture for where to find each one.
Which valves control flow or direction?
Not every valve is a simple on-off switch.
### Globe valves
A globe valve is built to regulate flow, not just stop it. NIBCO's globe and angle valve instructions say these valves "are used to start, stop or throttle the flow of fluids in piping systems." To throttle, you turn the handwheel to a spot between full open and full closed. NIBCO adds that flow is stopped "by forcing the disc down onto the valve body seat."
### Check valves
A check valve lets water flow one way and closes if it tries to reverse. NIBCO describes its non-return globe valve as "a directional valve operated by gravity to prevent backflow." It adds that the non-return feature "will only operate in the direction of the flow arrow on the side of the valve." NIBCO says that model must be installed with fluid flow in the same direction as the flow arrow. When you replace any check valve, match the arrow to the direction the water moves.
### Backflow preventers
Backflow preventers protect the drinking water supply. Phoenix's adopted code says the drinking water system must be built and kept up to prevent contamination from cross connections. It lists a range of approved devices and assemblies, each matched to a degree of hazard, from air gaps and vacuum breakers to testable backflow prevention assemblies.
At home, the one you see most is at the hose bibb. The code says hose bibbs, sill cocks, wall hydrants and other hose connections need a vacuum breaker. That can be an atmospheric-type or pressure-type vacuum breaker, or one permanently attached to the hose connection. The code exempts a few outlets, including water heater and boiler drain valves meant only for draining the tank. Irrigation systems carry their own requirements. See backflow preventers for sprinkler systems in Arizona.
Which valves protect against pressure and heat?
These valves work automatically. Leave their settings alone unless you know exactly what you're doing.
### Pressure-reducing valves
A pressure-reducing valve, or PRV, lowers incoming water pressure. The City of Phoenix says customers install a pressure regulator "on the customer's side of the water meter," and that private pressure regulators are the responsibility of the homeowner. Phoenix's adopted code sets the limit. Where static pressure inside a building is over 80 psi, it requires an approved PRV with a strainer. The PRV must meet ASSE 1003 or CSA B356 and bring the pressure down to no more than 80 psi static. The code makes exceptions, including service lines to sill cocks and outside hydrants. The code also says the valve must be designed "to remain open to permit uninterrupted water flow in case of valve failure." For more, see whether you need a pressure-reducing valve.
### Temperature and pressure relief valves
Every tank water heater needs one. Phoenix's adopted code requires an approved, self-closing (levered) pressure and temperature relief valve on storage water heaters that operate above atmospheric pressure. It also says the relief valve "shall not be used as a means of controlling thermal expansion," and requires the discharge pipe to discharge through an air gap located in the same room as the water heater. If yours drips, read why a water heater pressure relief valve leaks.
### Vacuum relief valves
Less common, but required in one situation. The code says bottom-fed water heaters and bottom-fed tanks connected to water heaters "shall have a vacuum relief valve installed."
Where does the code require valves in a house?
Beyond the fixture stops above, Phoenix's adopted plumbing code requires full-open valves in specific spots. In a house, the ones that matter most are:
- On the building water service pipe from the public water supply, near the curb.
- On the water distribution supply pipe at the entrance into the structure. That's your main house shutoff.
- On the discharge side of every water meter.
- On the water supply pipe to every water heater.
A few more rules help you in an emergency. The code says access "shall be provided to all full-open valves and shutoff valves," and that "Service and hose bibb valves shall be identified." Every valve also has to be safe for drinking water: "Valves intended to supply drinking water shall meet the requirements of NSF 61."
### Quick reference
| Valve | What it does | Where it typically goes |
|---|---|---|
| Ball valve | Quarter-turn on-off shutoff | Main shutoffs and other on-off points |
| Gate valve | Multi-turn on-off shutoff | Older main shutoffs |
| Fixture stop | Shuts off one fixture | Under sinks, behind toilets, at the washer |
| Globe valve | Starts, stops or throttles flow | Where flow needs adjusting |
| Check valve | Lets water flow one way only | Where water must not reverse |
| Backflow preventer | Keeps contaminated water out of the supply | Hose bibbs, irrigation and other cross connections |
| Pressure-reducing valve | Lowers incoming water pressure | Customer side of the water meter |
| Relief valve | Releases excess temperature and pressure | On the water heater tank |
Once you know what's what, the next step is knowing your main valve actually works. See how to test your main water shut-off valve.
Not sure what a valve in your house does? Ask us. We're licensed and insured, and every estimate is free with upfront pricing.