Plug valve
Encyclopedia
Plug valves are valve
s with cylindrical or conically-tapered "plugs" which can be rotated inside the valve body to control flow through the valve. The plugs in plug valves have one or more hollow passageways going sideways through the plug, so that fluid can flow through the plug when the valve is open. Plug valves are simple and often economical.
When the plug is conically-tapered, the stem/handle is typically attached to the larger diameter end of the plug. Plug valves usually do not have bonnets but often have the end of the plug with the handle exposed or mostly exposed to the outside. In cases like that, there is usually not much of a stem. The stem and handle often come in one piece, often a simple, approximately L-shaped handle attached to the end of the plug. The other end of the plug is often exposed to the outside of the valve too, but with a mechanism which retains the plug in the body.
The simplest and most common general type of plug valve is a 2-port valve, which has two positions, open to allow flow, and shut (closed) to stop flow. Ports are openings in the valve body through which fluid can enter or leave. The plug in this kind of valve has one passageway going through it. The ports are typically at opposite ends of the body; therefore, the plug is rotated a fourth of a full turn to change from open to shut positions. This makes this kind of plug valve a quarter-turn valve. There is often a mechanism limiting motion of the handle to a quarter turn, but not in glass stopcocks.
Slightly conically-tapered metal (often brass
) plug valves are often used as simple shut-off valves in household natural gas
lines.
It is also possible for a plug valve to have more than two ports. In a 3-way plug valve, flow from one port could be directed to either the second or third port. A 3-way plug valve could also be designed to shift flow between ports 1 and 2, 2 and 3, or 1 and 3, and possibly even connect all three ports together. The flow-directing possibilities in multi-port plug valves are similar to the possibilities in corresponding multi-port ball valve
s or corresponding multi-port valves with a rotor. An additional possibility in plug valves is the have one port on one side of the plug valve and two ports on the other side, with two diagonal and parallel fluid pathways inside the plug. In this case the plug can be rotated 180° to connect the port on the one side to either of the two ports on the other side.
Stopcocks used in laboratory glassware
are typically forms of conically-tapered plug valves. When fused with the glassware, the valve bodies are made of glass. Otherwise, they can be made of an inert plastic such as Teflon. The plugs can be made of a similar plastic or glass. When the plug is made of glass, the handle and plug are fused together in one piece out of glass. When glass is used for both the stopcock body and the plug, the contacting surfaces between them are special ground glass surfaces (see Laboratory glassware
) often with stopcock grease in between. Special glass stopcocks are made for vacuum
applications, such as in use with vacuum manifold
s. Stopcock grease is always used in high vacuum applications to make the stopcock air-tight. Also if the plug valve is "locked" from being in the open or closed position for an extended amount of time lubricant can be added through the greaser with the valve in service.
Valve
A valve is a device that regulates, directs or controls the flow of a fluid by opening, closing, or partially obstructing various passageways. Valves are technically pipe fittings, but are usually discussed as a separate category...
s with cylindrical or conically-tapered "plugs" which can be rotated inside the valve body to control flow through the valve. The plugs in plug valves have one or more hollow passageways going sideways through the plug, so that fluid can flow through the plug when the valve is open. Plug valves are simple and often economical.
When the plug is conically-tapered, the stem/handle is typically attached to the larger diameter end of the plug. Plug valves usually do not have bonnets but often have the end of the plug with the handle exposed or mostly exposed to the outside. In cases like that, there is usually not much of a stem. The stem and handle often come in one piece, often a simple, approximately L-shaped handle attached to the end of the plug. The other end of the plug is often exposed to the outside of the valve too, but with a mechanism which retains the plug in the body.
The simplest and most common general type of plug valve is a 2-port valve, which has two positions, open to allow flow, and shut (closed) to stop flow. Ports are openings in the valve body through which fluid can enter or leave. The plug in this kind of valve has one passageway going through it. The ports are typically at opposite ends of the body; therefore, the plug is rotated a fourth of a full turn to change from open to shut positions. This makes this kind of plug valve a quarter-turn valve. There is often a mechanism limiting motion of the handle to a quarter turn, but not in glass stopcocks.
Slightly conically-tapered metal (often brass
Brass
Brass is an alloy of copper and zinc; the proportions of zinc and copper can be varied to create a range of brasses with varying properties.In comparison, bronze is principally an alloy of copper and tin...
) plug valves are often used as simple shut-off valves in household natural gas
Natural gas
Natural gas is a naturally occurring gas mixture consisting primarily of methane, typically with 0–20% higher hydrocarbons . It is found associated with other hydrocarbon fuel, in coal beds, as methane clathrates, and is an important fuel source and a major feedstock for fertilizers.Most natural...
lines.
It is also possible for a plug valve to have more than two ports. In a 3-way plug valve, flow from one port could be directed to either the second or third port. A 3-way plug valve could also be designed to shift flow between ports 1 and 2, 2 and 3, or 1 and 3, and possibly even connect all three ports together. The flow-directing possibilities in multi-port plug valves are similar to the possibilities in corresponding multi-port ball valve
Ball valve
A ball valve is a valve with a spherical disc, the part of the valve which controls the flow through it. The sphere has a hole, or port, through the middle so that when the port is in line with both ends of the valve, flow will occur. When the valve is closed, the hole is perpendicular to the ends...
s or corresponding multi-port valves with a rotor. An additional possibility in plug valves is the have one port on one side of the plug valve and two ports on the other side, with two diagonal and parallel fluid pathways inside the plug. In this case the plug can be rotated 180° to connect the port on the one side to either of the two ports on the other side.
Stopcocks used in laboratory glassware
Laboratory glassware
Laboratory glassware refers to a variety of equipment, traditionally made of glass, used for scientific experiments and other work in science, especially in chemistry and biology laboratories...
are typically forms of conically-tapered plug valves. When fused with the glassware, the valve bodies are made of glass. Otherwise, they can be made of an inert plastic such as Teflon. The plugs can be made of a similar plastic or glass. When the plug is made of glass, the handle and plug are fused together in one piece out of glass. When glass is used for both the stopcock body and the plug, the contacting surfaces between them are special ground glass surfaces (see Laboratory glassware
Laboratory glassware
Laboratory glassware refers to a variety of equipment, traditionally made of glass, used for scientific experiments and other work in science, especially in chemistry and biology laboratories...
) often with stopcock grease in between. Special glass stopcocks are made for vacuum
Vacuum
In everyday usage, vacuum is a volume of space that is essentially empty of matter, such that its gaseous pressure is much less than atmospheric pressure. The word comes from the Latin term for "empty". A perfect vacuum would be one with no particles in it at all, which is impossible to achieve in...
applications, such as in use with vacuum manifold
Manifold (general engineering)
A manifold, in systems for moving fluids or gases is a junction of pipes or channels, typically bringing one into many or many into one.-Applications:*Heated-manifold direct-injection die casting for zinc die casting....
s. Stopcock grease is always used in high vacuum applications to make the stopcock air-tight. Also if the plug valve is "locked" from being in the open or closed position for an extended amount of time lubricant can be added through the greaser with the valve in service.