Types of Ball Valves
Ball valves are quarter-turn valves used in residential, commercial, and institutional applications to control the on-off flow of liquids and gases. They are available in a range of sizes, materials, and connection types.
- The Valve Body – A pressure vessel that contains the components needed to control or shut off the flow through a pipe. It is designed to connect two or more sections of pipe or tubing to each other.
- The Ball – A sphere with a flow path (hole or tunnel) through the center of it and a connection point for a shaft to rotate it.
- The Seats – Round donut shaped discs that form a seal between the body and ball.
- The Stem – A shaft that connects the internal ball to the outside of the valve to facilitate rotation of the ball.
- The Packing – Flexible seals that fit around the shaft and prevent the media travelling through the valve from escaping externally.
- The Bonnet – The part of the valve body that houses the stem and packing.
- The Operator or Actuator – An external device designed to rotate the stem of the valve. This can be a lever, a gear, a motor operated gear (Electric Actuator), or a pneumatic/hydraulic actuator.
Trunnion Mounted Ball Valve – A trunnion mounted ball valve has additional mechanical anchoring at the top and bottom on the ball. This special mounting is suitable for larger and higher pressure valves. Moreover, this design allows for reduction in valve torque as the ball is supported in two places. Every CAMERON T31 ball valve is trunnion mounted. The trunnion mounted stem absorbs the thrust from the line pressure, preventing excess friction between the ball and seats, so even at full rated working pressure operating torque remains low.
- Floating Ball Valve– A floating ball valve is not held in place by a trunnion, and instead is attached only to the stem. This sometimes causes the ball to float slightly downstream. However, when this happens, the ball presses against the seat, creating a positive seal.
- Rising Stem Ball Valve– A rising stem ball valve incorporates tilt-and-turn operation, eliminating seal rubbing which is one of the primary causes of valve failure. When the valve is closed, the core is wedged against the seat, ensuring positive shutoff. When the valve is open, the core tilts away from the seal and the flow passes uniformly around the core face. The Cameron ORBIT rising stem ball valve utilizes this operating principle, delivering fast, low-torque operation and long term reliable performance. Additionally, the valve is able to eliminate localized high- velocity flow that typically creates uneven seat wear exhibited by ordinary ball, gate, and plug valves.
- Additionally, there are three basic types of bores for ball valves: full port, reduced port (also known as standard port), and v-port. These four types have different constructions and purposes.
- Full-Port Ball Valve – A full-port, also known as a full-bore, ball valve has a bore internal diameter (ID) approximately equal to the pipeline ID. This allows for reduced friction and pressure loss across the valve. With a full-port ball valve there is no restriction to the flow of fluid, but the valve can be more expensive. This type of bore is ideal for situations where pigging may be necessary. The Cameron TBV series split-body, full-port, flanged ball valve combines its sealing technology and design expertise with the versatility to solve even the most demanding applications. This technology is widely used in the chemical, petrochemical, and refining industries.
- Reduced-Port Ball Valve – A reduced-port, also known as a reduced-bore, ball valve is a valve in which the bore is reduced to one or two nominal sizes lower. This provides a more restricted flow path, generally resulting in higher energy losses. Cameron TK ball valves offer both full- port and reduced-port valves. Known for its robust design, superior sealing areas and stainless steel overlays, the TK brand is widely recognized as the leader in providing valve solutions for the oil and gas industries’ most severe service applications.
- V-Port Ball Valve – A v-port ball valve has either a “v” shaped ball or a “v” shaped seat. This type of valve also is known as a control valve in which the flow velocities need to be controlled as required per the application.
Ball valves can be used in a variety of applications and markets, such as transmission and storage, gas processing, industrial, and many more. Jeffery Joseph, product manager for the CAMERON ball valves, explains that ball valves provide reliable leak protection which is especially beneficial in gas applications. Ball valves have low pressure drop and can open and close quickly.
A variety of construction materials, trim options and designs make these valves extremely versatile. Ball valves, such as RING-O subsea ball valves, are commonly utilized in subsea applications on manifolds that require long service life at high pressures. Ball valves, including the Cameron TBV line of ball valves, also are used in cryogenic applications where compressed gas must be kept at a stable temperature in order to be moved efficiently.
Trunnion ball valve vs floating ball valve
Floating Ball Design
A floating design ball valve sandwiches the hollow ball between two or more cupped seats that form a tight seal between the body and the ball at the inlet and outlet ports of the valve body.
The ball is rotated (usually 90 degrees) by a shaft that protrudes outside of the valve body and is connected to some form of operator. For this reason, most ball valves are referred to as quarter turn valves. This shaft is not rigidly attached to the ball in order for the ball to pivot on the end of the shaft as it rotates on the axis of the ball. This is usually accomplished with a slot on top of the ball, perpendicular to the ball’s flow path. The cupped portion of the seats cradle the ball prevents it from moving down in the valve body.
The valve packing prevents the media from escaping the valve body through the stem opening in the bonnet. The most common type of packing today is chevron v-ring type packing. If you look at the cross section profile of this packing, it resembles the letter “V”. The outer diameter of the packing matches the bore of the bonnet. The inside diameter matches the outer diameter of the stem. Multiple rings of this packing are stacked on top of each other and the stem is inserted through the packing. A packing gland on top of the bonnet pushes down on the top of the “V” and causes the packing to expand and seals agains the stem and bonnet.
Seats are secured on the inside of the valve body around the outer diameter of the openings, or “Ports”, of the valve body. They are rigidly held into place in the valve body to form a tight seal around the port. The seats do not move in the floating ball design. The side of the seat that contacts the ball is usually cupped and the inner diameter of the seat is slightly larger than the hole in the ball.
When in the open position, the flow path in the ball is in line with the flow path in the body. The openings in the ball are aligned with the openings in the ports of the body. This allows flow from the upstream port to travel through the ball’s flowpath and out to the downstream pipe(s).
When the ball is in the closed position, the flow path in the ball is perpendicular to the flow path in the valve body. The solid parts of the ball covers both upstream and downstream cupped seat openings. The pressure in the upstream pipe pushes against the solid part of the ball which moves on its pivot point and is forced tightly against the downstream seat. This shuts off flow.
As the operator rotates the ball from the closed position, the ports in the body in relation to the ports in the ball create a variable size orifice which, as it gets larger, will increase the flow through the pipe. When moving from open to close, this orifice gets smaller and decreases flow.
Floating ball design valves are the most economical valves, but are limited by the amount of pressure the seats can handle.
Trunnion Mounted Ball Design
The trunnion design ball valve works nearly the same way as the floating ball except the seats are spring loaded against the ball and the ball does not pivot. The ball only rotates on its axis in this design.
In the trunnion mounted ball valve, the ball utilizes a second shaft and bearing on the bottom of the ball. This stem or “post” holds the bottom of the valve in place. The top of the ball is not slotted and the upper stem is rigidly attached to the ball. This prevents the ball from moving into the downstream seat.
Since the ball does not move into the seats, the seats must move towards the ball. Springs behind the seat push them tightly into the ball in order to make the seal.
Trunnion valves are very effective at sealing off very low pressures that would not be strong enough to move a floating ball into the downstream seat. They are also required on large diameter valves and high-pressure valves. The reason for this is the contact area of the seats in a floating ball is relatively small. From physics, we know force = Pressure x Area. The force on the downstream seat in a floating ball is derived from the process pressure in the upstream pipe pushing on the solid area of the ball in the closed position. If the pressure is high or the area is large, the downstream seat will be destroyed.
The tradeoff is that trunnion valves are much more expensive than floating ball designs.
Both floating ball and trunnion designs are available as multi-port valves by using elaborate flow paths in the ball and additional ports in the body.
Floating ball spheres is floating in medium pressure function, ball of displacement and physical produce certain tightly compressed the seal surface in exports, ensure outlet seal.
Floating ball valve small volume, light weight, simple structure, good sealing, but ball work under medium load all passed to export sealing ring .So we must consider sealing materials can withstand the work load. Ball media This structure, widely used in low-pressure valve.
Floating ball valve features and performance
Small volume, light weight, simple in structure and function, with freely floating ball can better guarantee seal; Ball valve with circular hole sphere as on-off pieces, in stem drive next ball around stem centre for 0 ~ 90 degree rotated, complete opening and closing functions; With compact structure, turning the characteristics of quick opening 90 degrees, can close the valve, cut pipeline medium; Sphere passage diameter and pipe diameter, the same small flow resistance, circulation ability; Stem to remove theatrical makeup and costume type, to eliminate the stem wear out the accident happened, to ensure the safe use of;
Trunnion ball valve sphere is fixed, do not produce mobile after pressurized. Trunnion ball valve with floating seat. After medium pressure, seat produce mobile, make seal tightly compressed in ball, to ensure that the seal. Usually in the upper and lower with ball bearing, operation with shaft torque is small, be applicable to the high pressure and large diameter valve.
Trunnion ball valve suitable for various in high pressure piping, used in the medium truncated or connect piping, choose different material, which applies to water, steam, oil products, liquefied petroleum gas, natural gas, coal gas, nitric acid, acetic acid, oxidizing medium, urea and so on widely used in petroleum chemical power water conservancy and other industries. Trunnion ball valve common driving way for worm gear, manual and electric and pneumatic. Most trunnion ball valve are flange connection, but also have welding form of trunnion ball valve.
Difference between the floating ball valve and the trunnion ball valve in appearance,sealing surface,working principle,application and characteristics:
The floating ball valve and the trunnion ball valve are easy to distinguish in appearance. If the valve body has a fixed shaft on the bottom, it must be the trunnion ball valve.
If the ball valve body has a device for injecting grease,it is basically a trunnion ball valve.However, if there is no injecting device,can we say it must be a floating ball valve? This is incorrect, because small size such as 2 “150LB trunnion ball valves are usually not filled with injecting device either.
2. Sealing surface
As the ball of the floating ball valve is floating, so under the pressure of the medium, the floating ball will move and against the downstream seat., so the seal of the floating ball valve belongs to the single-side seal.The ball of the trunnion ball valve cannot be moved, so the two sides of the trunnion ball valve both must be sealed.
Since the sealing principle is different, the requirements of the two ball valves on the sealing surface material are different, especially the sealing surface of the floating ball valve must be able to bear the pressure caused by the floating ball.
3. Working principle
The floating ball valve only has upper stem and the ball can have a slight displacement, so it is called floating ball valve.The trunnion ball valve ball has another stem at the bottom to fixed the position of the ball,so the ball can’t move.
The sealing of the floating ball valve is realized by the pressure of the medium,when the ball valve is closed, the floating ball is pressed against the sealing surface under the action of pressure to realize sealing.When the trunnion ball valve is closed, the ball does not produce displacement, but the floating seats will move and press against the ball under the action of the media pressure to realize sealing.
The floating ball valve is suitable for medium and low pressure and usually has a small diameter.The trunnion ball valve can be used in high pressure conditions and the size can be up to 60 inches.
The trunnion ball valve is a kind of double-block-and-bleed(DBB) valve, while the floating ball valve only seal the downstream side.The trunnion ball valve can block both upstream and downstream media. And when the pressure in the middle cavity is greater than the seat spring force, the seat will be pushed open to release the pressure inside the chamber to ensure safety.
To the floating ball valves,the trunnion ball valves are usually used longer,has smaller size and easier to operate.
The trunnion ball valve also has the function of automatic release pressure, when the medium temperature in the valve rises and causes abnormal pressure rise, the trunnion ball valve can automatically release the pressure without a relief valve,This is very important to ensure the safety of industrial production.
Under the pressure of the medium, the ball of floating type moves against downstream sealing. When the trunnion-mounted type works, the ball remains fixed. The trunnion ball valve is composed of an upper stem and a fixed shaft at the bottom, while the floating type is with an upper stem only. The floating type is widely used in small size and low pressure condition. On the contrary, the trunnion ball valves are often used in large size and high pressure condition.
The three aspects mentioned above are the main differences between them. Certainly, there are other perspectives. The trunnion-mounted type has the double block and bleed function (DBB), and its seat is more reliable with a metal seat support.
Source: Network Arrangement – China Valves Manufacturer – Yaang Pipe Industry Co., Limited (www.ugsteelmill.com)
(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)
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