Ball valve is mainly used to cut off, distribute and change the direction of medium flow in pipeline. V shaped ball valve opening also has a good flow adjustment function. Ball valve only needs to be operated with a rotation of 90 degrees and a small turning torque to close tightly. The completely equal valve body cavity provides a direct flow channel with little resistance for the medium.
Ball Valve has a simple structure and good sealing performance. It can configure smaller nominal diameter, lightweight, low material consumption, small installation size, small driving torque, simple operation, easy to realize quick opening and closing, and easy operation within a certain nominal passage range and maintenance. The ball valve is suitable for general working media such as water, solvents, acids and natural gas, but also for media with severe working conditions, such as oxygen, hydrogen peroxide, methane and ethylene.
1.Ball Valve types
2.Ball Valve Structure and Working Principles
3.Ball Valve Design Standard And Application
4.Advantages of Ball Valve
5.Maintenance of Ball Valve
6.Ball Valve Selection Guide
1. Ball Valve types
There are lots of ball valve variations, and new ball valve types are still emerging. According to the characteristics and uses of ball valves, ball valves can be divided into several types.
It can be divided into floating ball valve and trunnion mounted ball valve
a. Floating Ball Valve
Its main feature is that the sphere/ball has no support shaft/trunnion. The sphere/ball is supported by valve seats at both ends of the valve inlet and outlet. The valve stem and the sphere/ball are movably connected, as shown in Figure 1-1. The ball is sandwiched by two valve seats and is in a “floating state”. The ball can be freely rotated between two valve seats with the valve stem by a lever or other driving device. When the flow passageway of the ball is aligned with the valve passageway, the ball valve is in an open state. The flow is smooth, and the flow resistance of the valve is minimum. When the sphere/ball is turned 90°, the flow passageway of the sphere/ball is perpendicular to the valve passageway. The ball valve is in a closed state, and the sphere is pushed to the valve outlet (behind the valve) seat under the action of the fluid pressure to ensure tight sealing.
The main advantages of floating ball valves: simple structure, easy manufacturing, low cost, and reliable. The sealing performance of the floating ball valve is related to the fluid pressure. Under the same conditions, the higher the pressure, the easier to seal. But it should be considered whether the valve seat material can withstand the load transmitted to it by the ball, because the force generated by the fluid pressure on the ball will be completely transmitted to the valve seat. For larger size floating ball valves, because when the pressure is high, the operating torque will increase, and the weight of the ball itself is large. The pressure distribution generated by the weight on the sealing surface of the valve seat is uneven. Normally the pressure in the half circle on the horizontal plane of the bore diameter is small, and the pressure in the lower half circle is large. It will result uneven wear of the valve seat and leakage. Therefore, floating ball valves are generally suitable for valves size smaller than 8”.
b. Trunnion Mounted Ball Valve
The ball connected with the upper stem and lower trunnion, or is made into an integral coupling type ball, where the ball is forged (welded) with the upper trunnion and lower trunnion to be integrated on the bearing/trunnion plate. Hence, the ball move freely perpendicular to the valve body but not move along the channel axis. Therefore, when the trunnion mounted ball valve is in operation, all the force generated by the fluid pressure on the ball is transmitted to the bearing/trunnion. The ball will not be pushed towards valve seat. So the valve seat will be not subjected to excessive pressure. The Trunnion Mounted Ball valve has low torque, small deformation of valve seat due to excessive pressure. It has stable sealing performance, long service life, suitable for high pressure and larger valve diameter.The key to the sealing of a trunnion mounted ball valve is the correct selection of the seat design of spring-loaded valve seat. Properly design seat dimension, fully utilization of fluid pressure and spring force to meet the sealing requirements.
Can be divided into top-entry, side-entry, diagonal-entry and so on. For the side entry ball valve, according to the application and the valve size, the valve body has two types: one piece body type and split body. The split body ball valve is divided into two-piece type and three-piece type.
a. Top Entry Ball Valve
The characteristic of the top entry ball valve is the valve body is one piece body, cover up on top with bonnet, and the ball, seal ring and valve seat are all installed from the top of the valve body.
The advantages of Top-entry ball valves: When overhauling or replacing the valve seat, it is not necessary to remove the valve from the pipeline. It can open the bonnet inline and remove the ball. It is very suitable for underground pipelines, especially for nuclear energy industry. For 3 way ball valve, 4 way ball valve and multi-way ball valves, because of their large spheres/balls, it is very difficult to install or remove from either end of the valve, and the body cavity of the multi way ball valve itself is very large and heavy. Top entry ball valve is more suitable than the side entry ball valve.
The disadvantages of top entry ball valve is the size and weight, which usually very big and heavy. Generally, it is not suitable for high pressure application.
b. Side Entry Ball Valve
Side Entry One Piece Body
The ball is installed from one end of the valve, and the valve seat and the ball are fixed and compressed with a screw sleeve. This ball valve has a simple structure, lesser components, and is easy to manufacture and install. It is suitable for small diameters, especially for viscous or crystallizing media, such as urea, where the valve body needs to be made into a thermal insulation jacket.
Side Entry Split 2pcs Body Ball Valve
The vertical cross-section of the valve body along the channel axis is divided into asymmetrical left and right pieces. The ball is installed in body cavity space, and the left and right valve pieces are flanged or threaded.
Because the valve body is divided into two pieces, compared with the integral type, half of the valve body is lighter in weight, easy to cast (forged) and machined.
Side Entry Split 3pcs Body Ball Valve
For ball valves with larger nominal sizes, in order to facilitate manufacturing and assembly process, the side-entry three piece body design is often used. The valve body is divided into three pieces along the cross section which is perpendicular to the channel axis at the two valve seats bilaterally symmetrical to the valve stem. The valve appearance is equal and neat and manufacturing friendly. The disadvantage is due to flanged end will increase the weight.
2. Ball Valve structure and working principles
Ball valve is mainly constructed of valve body, seat, ball, valve stem, handle (or other driving device). The ball valve uses a ball with a round through hole as the opening and closing part. The ball rotates with the valve stem to achieve the opening and closing action. The main function of the ball valve is to cut off or connect. The working principle is to apply a certain torque on the upper end of the valve stem with the help of a handle or other driving device and transmit it to the ball, so that the ball rotates around the axis perpendicular to the flow passageway by 90°. When the hole of the sphere/ball and the valve center line of the body passage coincides or is vertical, it indicates that the ball valve has been fully opened or fully closed, so as to achieve the purpose of opening and closing the passageway.
3. Ball Valve Design Standard and Application
API 608 《Metal Ball Valves – Flanged, Threaded, and Welding End》
API 6D 《Specification for Pipeline and Piping Valves》
ISO 7121 《Steel ball valves for general-purpose industrial applications》
ISO 14313 《Petroleum And Natural Gas Industries-Pipeline Transportation Systems-Pipeline Valves》
BS EN ISO 17292《Metal Ball Valves for Petroleum, Petrochemical and Allied Industries》
AWWA C507 《Ball Valves, 6 In. Through 60 In. (150 mm Through 1,500 mm)》
ASME B16.5 《Pipe Flanges and Flanged Fittings NPS 1/2 Through NPS 24 Metric/Inch Standard》
ASME B16.10 《Face-to-Face and End-to-End Dimensions of Valves》
ASME B16.34 《Valves – Flanged, Threaded, and Welding End》
ASME B16.25 《Buttwelding Ends》
API 607 《Fire Test for Quarter-turn Valves and Valves Equipped with Nonmetallic Seats》
4. Advantages of Ball Valve
1）Low flow resistance, full port ball valve has almost zero flow resistance
2）Simple design, small in size and weight
3）Reliable tight seal. At present, the sealing surface material of ball valves is widely used plastic, which has good sealing performance. It can achieve complete sealing, zero leakage, and has been widely used in vacuum systems.
4）Operation friendly, fast open/close, fully open to fully closed with only 90° turn. Suitable for as a remote valve.
5）Maintenance friendly, simple configuration with dynamic seal which is easy to replace.
6）When fully open or fully close, ball and seat sealing surface is not contacted with medium when medium flow. Hence sealing surface will not be easily contaminated and eroded.
7）Wide application from small diameter up to few millimeter, large diameter up to few meters, and from high vacuum to high pressure is applicable.
8）The open close of ball valve has wiping effect, hence suitable for medium with floating particles.
5. Maintenance of ball valve
1）Inspect the appearance of ball valve;
2）Check if the actuator and related supporting system for oil leakage;
3) Check the ball valve body and accessories, flanges and other sealing points for leakage;
4) Ball valve blowdown, regular blowdown of the ball valve is an effective means to ensure the valve cavity and sealing system clean
5) Check the inner cavity of the ball valve, after the valve is drained, after 10-20 minutes interval, open the drain valve again to check the valve for leakage
6) For manual ball valve, fully open or fully closed more than twice, check whether the valve open close is functioned. Only one operator is allowed to operate. Excessive pressure and force are not permitted when operating the valve. For valves that are not operated for a long time or used in low temperature environments, there may be problems with foreign material accumulation or jam in the valve. Before operating the ball valve, you should first Inject a small amount of cleaning fluid or grease to protect the valve seal
7) Check if the operation of the fully open or fully closed valve is functioned, check whether there is a blocking phenomenon, if the valve torque is too large (single-person operation is difficult), the cleaning fluid should be injected to fully clean and move the valve
8) Fixed all problem identified.
6. Ball Valve Selection guide
1）For oil and natural gas pipelines and pipelines that need to be cleaned and buried under ground, select a full bore, fully welded ball valve structure; for a on ground valve, choose a ball valve with a full-port welded or flanged connection; For the pipeline and storage equipment of product oil, select flanged ball valve
2）In the gas pipeline system, it is advisable to choose a trunnion mounted ball valve that is strictly degreased and flange connection. For piping systems and devices of low-temperature media, low-temperature ball valves with extended bonnets should be selected.
3） On the pipeline system of the catalytic cracking device of the oil refining device, a rising stem type ball valve can be selected. In the equipment and piping system of corrosive media such as acid and alkali in the chemical system, it is appropriate to select a full stainless steel ball valve made of austenitic stainless steel with PTFE as the seat ring
4） Metallurgical systems, electric power systems, petrochemical installations, and high-temperature medium piping systems or devices in urban heating systems may use metal-to-metal sealed ball valves. When flow adjustment is required, worm gear drive, pneumatic or electric adjustment ball valve with V-shaped opening can be selected
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