Water Valves, Drains and Plumbing Manifolds

Valve type and body material: what the line carries

Valve function organizes this aisle, so start with the job. Gate and ball valves isolate a line, globe valves throttle flow, check valves and vacuum breakers stop backflow, and pressure-regulating valves hold a set downstream pressure in psi. Body material follows the fluid: bronze and brass suit water and general service, and for drinking water look for lead-free or NSF/ANSI 61 marking; cast iron suits larger lines and drains, and stainless steel is chosen for corrosive or hygienic duty. Steam needs a valve rated for its temperature and pressure, not just the pipe size.

Size, thread and pressure: getting the connection right

Valve size is the nominal pipe size, such as 1/2, 3/4 or 1 inch, and connections come threaded (NPT in North America), soldered, flanged or push-fit, so match the pipe system. NPT threads are tapered and need sealant. Pressure ratings are given in psi at a stated temperature, and the working pressure must stay below the lowest-rated part in the line. For a repair kit, such as one for a vacuum breaker or backflow assembly, match the exact model number, because internal parts differ even between valves of similar size.

Questions about Water Valves, Drains and Plumbing Manifolds

What is the difference between a gate valve and a ball valve?

A gate valve lowers a wedge across the flow and needs several turns to operate, while a ball valve uses a ball with a hole and moves between open and closed with a quarter turn. Ball valves seal well and are quick; gate valves are mostly used fully open or fully closed.

What does a vacuum breaker do?

It stops contaminated water being drawn back into the drinking water supply when pressure drops, by admitting air at the high point. It is fitted on hose bibs, irrigation lines and similar outlets, and repair kits must match the exact model.

How do I choose a pressure-regulating valve?

Match the pipe size and connection, then check the inlet pressure range and the adjustable outlet range in psi. The valve must be rated for the fluid and the temperature, since water, air and steam regulators are not interchangeable.