The plug valve is an angular stroke rotary motion manual valve with a cylindrical or conical rotary plug inside. It allows or prevents fluid straight-through flow through the valve body by rotating the rotary plug. A plug valve provides a straight passage through the port so fluid can flow through the open plug with minimal turbulence. It has one or more horizontal channels to allow flow through the valve when open. Plug valves are often used to move liquids or gases but rarely solids. Flow can be either fully open or fully closed in either direction. In addition, plug valves are simple and generally economical.
The typical plug valve consists of a body, bonnet, stem, and plug.
The plug is the opening and closing part of the plug valve, which is cylindrical or conical. Cylindrical cocks have a rectangular or circular channel section, and conical cocks have a rectangular, trapezoidal or circular channel section. These shapes make the structure compact and lightweight, but cause a certain pressure drop.
The stem of the valve connects the disc with the actuator. It helps the movement of the actuator to the plug disc so as to open or close the plug disc. The plug valve has a small stem that connects to the disc.
(3)The Plug Valve Body
The body connects to the pipes through an end connection.
The globe valve is a forced sealing valve. It refers to a valve where the closing member (disc) moves along the centerline of the valve seat. The opening and closing parts of the globe valve are plug-shaped discs. It’s sealing surface is flat or conical, and the disc moves linearly along the center line of the valve seat.
The typical globe valve composes of a body, bonnet, stem, disc, seat and basket.
The globe valve body is the main pressure-bearing structure of the valve,which is easy to identify because it constitutes the mass of the valve. It contains all the internal parts of the valve that touches with the substances that the valve controls. The valve cover is connected to the valve body and contains the fluid, gas or slurry.
Seat rings provide a stable, uniform and replaceable closing surface. The valve seat is usually screwed in or screwed in. This pushes the cage down against the lip of the seat and secures it securely to the body.
The stem of globe valve links the actuator with the inside of the valve and transmits the driving force. The stem of the actuator control valve is smooth and the stem of the manual valve is threaded.
The bonnet is ready for a leak-proof closure to the valve body. The threaded portion of the stem goes through a hole in the bonnet with matching threads. Globe valves may have a screw-in, union or bolted bonnet.
1.The sealing performance of the plug valve is better than that of the globe valve.
2.Globe valves are better than plug valves for flow through.
3.The globe valve has a long stroke and slow opening speed. The plug valve is used for frequent operation, and it opens and closes quickly and easily.
4.Due to the change in the flow direction of the medium through the valve, the small flow resistance of the globe valve is high. The fluid resistance of the plug valve is small.
5.The plug valve is simple in design and low in cost.
Plug valves are often used on low-temperature, low-flow pipelines because their spool seals are sensitive to high temperatures. The use of globe valves is extremely common, but due to the large opening and closing torque and the long structure length, the nominal diameter is usually limited to less than 250mm, and some are up to 400mm, but special attention should be paid to the direction of inlet and outlet when selecting. Generally, most of the globe valve medium below 150mm flows in from the bottom of the valve disc, and most of the globe valve medium above 200mm flows in from the top of the valve disc. This is due to the closing torque of the valve. In order to reduce the opening or closing torque, generally more than 200mm globe valves are equipped with internal bypass or external bypass valve.
Plug valves and ball valves are technically the same valves because they perform the same functions and have similar features. And they both have a wide range of uses. But what are the differences between a plug valve and a ball valve? Let’s start with a fundamental understanding of what plug and ball valve are.
What are Ball & Plug Valves?
(1) Plug Valves
Shaped like a cone or cylinder, a plug valve uses a rotating plug inside the body of a valve to control fluid flow (see the image above). These types of valves have one or more horizontal passageways to allow flow through the valve when open. Plug valves are often used to move liquids or gases, but rarely if ever used to move solids. They typically have two ports but can also have three or more depending on the application.
(2) Ball Valves
The ball valve is a valve that uses a ball with a circular channel as the opening and closing part, and the ball rotates with the valve stem to realize the opening and closing action. The opening and closing part of the ball valve is a ball with a hole, which rotates around the axis perpendicular to the channel, so as to achieve the purpose of opening and closing the channel. Ball valves are mainly used to open and close pipelines and equipment media.
The ball valve is evolved from the plug valve. It has the same 90 degree rotation lifting action, the difference is that the cock body is a sphere with a circular through hole or channel through its axis. The ratio of the spherical surface to the channel opening should be such that when the ball rotates 90 degrees, all spherical surfaces should appear at the inlet and outlet, thereby truncating the flow. The ball valve can be closed tightly with only a 90-degree rotation operation and a small torque. The completely equal body cavity of the valve body provides a low-resistance, straight-through flow path for the medium.
It is generally believed that the ball valve is most suitable for direct opening and closing, but recent developments have designed the ball valve so that it can be used for throttling and flow control. The main features of the ball valve are its compact structure, easy operation and maintenance, suitable for general working media such as water, solvent, acid and natural gas, and also suitable for media with harsh working conditions, such as oxygen, hydrogen peroxide, methane and ethylene. The ball valve body can be integral or combined.
Differences Between Ball and Plug Valves
In terms of basic function and use, ball and plug valves are extremely similar. Both are control valves that are utilized in various piping units to produce tight shut-offs. They all operate on the same basic premise, with a perforated disc controlling the flow of the medium. They do, however, differ in a number of ways.
Here are some of the key distinctions between ball valves and plug valves:
Bored discs are found at the center of both ball and plug valves. A ball valve has a hollow center and a spherical disc. A conical or cylindrical disc with drilled openings runs through a plug valve. In a ball valve, the disc or ball is smaller than the disc or plug in a plug valve. A plug valve can give a tighter shut-off than a ball valve because of this. In comparison to a ball valve, plug valves are also smaller. Plug valves can be easily placed in smaller units due to their lower footprint.
(2) Working Principle
The plug valve gave way to the ball valve. They both rotate at 90 degrees, but the “plug” is either a plug or a ball with a circular through hole or channel going through its axis. The ball and ports should look like this: the sphere will appear as a sphere at the intake and outlet when rotated by 90 degrees, cutting off the flow. The port of the ball valve can not only be circular, but also V-shaped (v port ball valve) and T-shaped (t port ball valve). The upper sections of the plug valve, the conical plug, and the conical pressure-formed body surface, are sealed with packing between the plug and the space between the body. Because it normally does not have bonnets and instead has the handle exposed outdoors at the end, plug valves are simple and often cost-effective.
In terms of cutting performance, plug valves outperform ball valves. However, this isn’t readily apparent. The plug valve’s sealing surface is substantially larger than the ball valve’s and provides a superior sealing effect but at the cost of greater torque and a smaller diameter. To reduce medium erosion and valve tightening over time, the ball valve should be used for switching pipeline medium rather than as a throttle valve.
With the advancement of sealing technology, the sealing effect of the ball valve has greatly improved. So we can say that the plug valve is used when the sealing requirements are stringent but the diameter is small, and the ball valve is used when the sealing effect is not stringent but the diameter is large.
(4) Plug Valve Is Lower Cost
The bushing entirely covers the “plug” on the plug valve, preventing wear on the valve body and plug. The valve may be repaired and updated by replacing the bushing and top seal, which can meet the long-term service requirements of 300°C. This temperature range provides significant advantages over alternative hard-sealed metal ball valves.
Ball and plug valves are control valves that are used to start and stop the flow of the medium. The sealing surface of the plug valve is much larger than that of a ball valve. The cylindrical or conical plug in the valve has a larger surface area so it can provide a better seal. However, a larger surface area also translates to greater torque. The high torque makes the valve inflexible and difficult to operate.
Ball valves, on the other hand, provide torque-free operation. The smaller surface area can lead to low sealing performance but new advancements in chemical sealants and seal injections mean ball valves can easily overcome this problem. Ball valves are less heavy than plug valves. Since plug valves feature a solid disc or plug in the center that is larger in size, it is heavier as well. This is the reason why plug valves are usually used in smaller applications as large-sized plug valves are expensive to make and can get really heavy.
Control valves need regular maintenance to keep working effectively. Ball valves are difficult to maintain as the ball or disc is located deep inside the valve and cannot be easily accessed. In fact, one of the main criticisms of ball valves is that over time, the body cavity of the valve accumulates particles from the medium that is then difficult to remove. Plug valves are easier to maintain as the plug can be easily removed and cleaned. This also gives easy access to the rest of the valve body so it can be maintained without much hassle. Plug valves have a simpler construction, they don’t have a lot of moving parts. They are also smaller in size than most regular valves. This makes it easier to repair and maintain.
(7) Control Capability
Ball valves can be controlled using manual, electric, hydraulic, pneumatic, and many other kinds of actuators. They are easy to open and close and require very little force even when operating under high-pressure conditions. Plug valves can be operated using manual and electric actuators. They can be operated through pneumatic actuators as well but they are very expensive to install. Plug valves can be difficult to open and close in high-pressure operations due to the high amount of torque. This is the reason why plug valves are usually not used for larger applications.
Control valves such as ball and plug valves are utilized to provide bubble-tight seals in a variety of applications. Plug valves seal better, but they’re difficult to use and too expensive and heavy for large-scale applications. Ball valves may not have the best sealing capabilities, but they are simple to operate and scale up for bigger applications.