four-way cock
A cock connected with four pipes or ports, and having two or more passages in the plug, by which the adjacent pipes or ports may be made to communicate; formerly used as a valve in the steam engine, and for various other purposes.
four-way cock: valve with four ports and crossover passages
A four-way cock is a rotatable plug valve with four external ports arranged around its body and internal passages that allow any two or more ports to communicate depending on the plug's angular position. Unlike a simple two-way stopcock, it provides multiple flow paths through a single valve unit, making it useful where space is tight or where different fluid circuits must be switched without installing separate valves.
The plug itself is the rotating element, typically conical or cylindrical, drilled with one or more diagonal or perpendicular passages. As the plug turns, these internal channels align with different combinations of the four outer ports. A quarter-turn (90 degrees) between positions is common, though some designs require different angles. The plug is held in place by a gland nut and sealed with packing material or a ground brass-on-brass fit to prevent leakage.
Historical and Modern Use
Four-way cocks were standard on stationary steam engines, where they routed boiler steam, exhaust, and sometimes water between the engine cylinder, condenser, and manifolds. The design allowed an operator to switch operating modes or isolate sections with a single lever movement. Today they appear less frequently in new steam plants, having been replaced by solenoid or gate valves in piped systems, but remain useful in hydraulic test benches, laboratory gas apparatus, and compressed air control panels where manual operation and compact switching are valued.
The main wear point is the plug itself. If packing material degrades or the ground surfaces corrode, leakage increases and rotation becomes stiff. Hard water, steam condensate, and aggressive gases accelerate this. Replacement plugs are expensive and require precise boring, so many old cocks are rebuilt in place by experienced fitters or retired from service.
The name describes the geometry simply: four ports on the body, plus internal cock (passage-switching) action. Related terms include three-way cock (three ports) and stopcock (two ports). In modern specification documents you may see four-way cock listed as "four-port selector valve" or "four-port ball valve" if it uses a spherical plug instead of a conical one, though the older plug design remains more common in heritage and pressure-test equipment.