What is a Plug valve?

Plug valves are valves 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 such cases, 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 that retains the plug in the body.

The simplest and most common general type of plug valve is a 2-port valve with 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 valves or corresponding multi-port valves with a rotor.

An additional possibility in plug valves is to 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

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If you are in the valve world at all, you know that the plug valve oftentimes gets a bad rap. There are different reasons for this. One being that the maintenance for these valves is greater than that of other valves. They need to be lubricated while out in the field and more times than not, this is overlooked.

Secondly, due to the corrosiveness and high temperatures of the substances flowing through the plug valves , they tend to wear much quicker than that of some other valves. This means they require patching and maintenance on a regular basis.

Lastly, the plug valve is not the valve of choice when it comes to throttling. You will want a v port, butterfly or ball valve in those types of applications.

On a good note, the plug valve does not clog. And one of the most common uses for a plug valve would be in our homes or businesses where we utilize gas services. The brass, 2 port valve, which is used in gas lines, is conically shaped and its structure bares a handle. When the handle is turned to 90 degrees from the inlet and outlet ports of the valve, the valve flow is shut off. For the gas to flow though the pipes, the handle and plug would need to line up with the inlet and outlet ports of the valve body.

A straightforward description of a plug valve is best described as a rotational valve with a tapered disk resembling that of a plug.This plug or disk sits “long ways” in the valve and has a passageway bored through the center in order to accommodate passing air or fluids. This type of control for corrosive or high temperature air/liquids is economical and simple. With a 2 port valve there are two positions, open and shut. There are also multi-port valves available in the plug valve for different more complex type applications. In applications where there are more than 2 ports, you may have a need for a soft rubber overlay for a sure-tight shut off.Different types of seals are based upon gaskets. Some plug valves close against the gasket and some close directly on the seat.

Many oil field service companies, vacuuming devices and applications which are dealing with glassware stopcocks which create glass products, still utilize plug valves. It does indeed seem to be a dying breed of valves, but with the right material, the proper gasket/seat in a particular application, you may see that a plug valve can be successful for you…especially when expenses plays a factor in your decision.

To assist you better with your valve decision, make sure you contact your Valtorc sales specialist today. They can better educate you on what’s best for you and your application to obtain the maximum results of success.

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