A petcock is a miniature valve typically installed at the lowest point of a tank, radiator, or piping run to drain liquid, or at a high point to vent trapped air. They often feature a simple T-handle and a tapered plug design, operating with a quarter turn. Because they lack robust sealing mechanisms, they are restricted to low-pressure utility or automotive applications rather than process lines.
Open the petcock on the bottom of the compressor tank to blow out the accumulated condensate before it rusts the shell.
Over-tightening a brass petcock will snap the handle right off; they only need to be snug to seal against low pressure.
Also heard as
- drain valve
- bleeder valve
Related terms
Bleeder
A small vent or drain valve used to release pressure or fluid, especially between two block valves.
Plug valve
A quarter-turn valve that rotates a tapered or cylindrical plug with a port through it to start or stop flow.
Needle valve
A small valve with a long tapered stem tip that meters tiny flows with fine adjustment.