Drain valves are used to drain water or other liquids from pipes, tanks, radiators and other systems by providing an opening where the liquid can be released.

Drain valves are often installed on water heaters, HVAC systems, pools, irrigation systems, industrial tanks and piping to allow drainage for maintenance or repairs.

Drain valves work by manually or automatically opening a barrier that allows liquids to drain out through an outlet and be released from the system.

Common types of drain valves include ball valves, gate valves, globe valves, plug valves, butterfly valves and stopcocks. Each has advantages for certain drain applications.

Most drain valves are operated manually using a handle, wheel or switch. You rotate the handle to open and close ball valves and butterfly valves. For gate and globe valves, you lift or turn the handle to raise or lower an internal gate.

Drain valves should be replaced when they start leaking, no longer fully open or close, or have corrosion and mineral buildup that impedes function. Routine maintenance helps determine when replacement is needed.

Drain valves should be periodically inspected, exercised to open and close fully, and have any debris or mineral deposits cleaned out. Replace worn handles, gaskets and washers as needed.

Common drain valve sizes include 3/4 inch, 1 inch, 1 1/4 inch, 1 1/2 inch and 2 inches. The required size depends on the piping, flow rate and drainage application.

Drain valves are constructed from materials like brass, bronze, cast iron, stainless steel, PVC, and other metals and plastics suitable for liquids and temperatures.

Some ball valve and butterfly valve designs allow them to regulate, throttle or partially close off flow as well as completely drain systems.

Drain valves should be opened slowly and cautiously to avoid rapid drainage and water hammer. Wear eye protection and close an upstream valve first if needed.

Drain valves can be automated by actuators.