Pneumatic Ball Valve 

What is a pneumatic ball valve? 

A pneumatic ball valve is a type of ball valve that uses a pneumatic actuator. This type of valve is suitable for on and off applications. Pneumatic ball valves are quick to operate which helps to save time. Pneumatic ball valves can be automated or semi-automated depending on your preferences. The working of a pneumatic ball valve depends on the rotation of a ball with a bore. The ball in a pneumatic ball valve has a hole in its middle section. It is through this hole that the fluid in a pneumatic ball valve passes as it comes from the piping system. Pneumatic ball valves open/close when the valve actuator makes a quarter turn to either allow fluid flow or block fluid. Pneumatic ball valves are made of strong materials mostly of metals like stainless steel, carbon steel, and brass among other materials. The strong material is mostly used to make the valve body which is the main component that determines the strength of the valve against high-pressure applications. Pneumatic ball valves are of various types which makes these valves useful in many applications such as involving gases and liquids. 

Figure: Pneumatic actuated ball valve.

How does a pneumatic ball valve work?

A pneumatic ball valve uses a pneumatic actuator with a rack and pinion gears to produce mechanical energy suitable for closing or opening fluid flow. A pneumatic ball valve depends on compressed air to generate pressure energy which is converted into mechanical energy. In a pneumatic actuator, when pneumatic pressure is applied, the piston and rack move linearly causing the pinion gear to rotate. The pinion gear then rotates a drive shaft that rotates the pneumatic ball valve stem. The ball in a pneumatic ball valve is connected to the valve stem. The stem is connected to the pneumatic actuator. To open a pneumatic ball valve, the actuator is turned on, and using actuator rack and pinion, it rotates the stem for 90^o which also rotates the valve ball at the same 90^o. When the ball is rotated a quarter turn, it helps to make the ball hole in line with the pipeline and thus allowing fluid to flow. In this case, the pneumatic ball valve is said to be open. To close the pneumatic ball valve, the actuator turns the valve stem in an anticlockwise direction for an angle of 90^o. This makes the stem also rotate the valve ball in the same anticlockwise direction for 90^o. At this stage, the ball bore is now perpendicular to the pipeline and is blocking the fluid flow. The valve is now said to be in a closed state and no fluid is flowing. 

Figure: Working of a pneumatic ball valve.

Types of pneumatic ball valves 

Pneumatic actuated trunnion ball valve 

This is a pneumatic ball valve in which the ball turns in a fixed position. The ball in a pneumatic trunnion ball valve is held in position by a shaft on both bottom and top sides making it unable to move in the lateral direction. A pneumatic actuated trunnion ball valve seal is created when fluid pressure forces the floating seat ring against the ball or by pro-stressing the ball and seats. The trunnion or shaft in a pneumatic actuated trunnion ball valve helps to absorb pressure from the fluid flow. As such, the contact between the seat and ball is not stressed excessively and the opening/closing torque remains lower making a pneumatic trunnion ball valve easy to operate. Pneumatic ball valves with high operating pressure and large diameters are mostly designed with a trunnion ball. 

Figure: Pneumatic actuated trunnion ball valve.

Two-piece pneumatic ball valve 

This is a pneumatic ball valve that is divided into two pieces. One piece of this pneumatic ball valve contains a valve body and one end joint. The second piece of the valve is attached to the first piece and it fixes the trim to its position. The second piece also contains the other end joint for the opposite side. One advantage of having a two-piece pneumatic actuated ball valve is that it can be dismantled for repair work, cleaning, and maintenance. However, a two-piece pneumatic actuated ball valve needs to be removed from the pipeline completely to separate the two pieces. 

Figure: Two-piece pneumatic ball valve.

Three-piece pneumatic ball valve 

This is a pneumatic ball valve whose body is divided into three parts. The three parts are the valve body and two ends joining the pneumatic ball valve to the piping system. The three parts are connected using bolts and nuts. A three-piece pneumatic actuated ball valve makes it easy to remove the central valve component which is the part that contains the ball, stem, and seat from the pipeline. A three-piece pneumatic actuated ball valve enhances easier removal of dirt, exchange of seals and seats without necessarily removing the valve from the piping system. One of the main advantages of a three piece ball valve is that it can be repaired or cleaned without removing it from the piping system. However, a three-piece pneumatic ball valve is more expensive when compared to other valves. 

Figure: Three-piece pneumatic ball valve.

Three-way pneumatic ball valve 

This is a pneumatic actuated ball valve with three ports. A Three-way pneumatic ball valve employs T or L configurations which depend on the required flow pattern. A three-way pneumatic ball valve is best suitable for mixing or diverting fluid flow in different applications. The T-configuration of a three way ball valve is used to make a valve that can mix two fluid streams into one stream. The mixing of two fluids in a pneumatic ball valve is done by merging the two streams at the inlet. Also, the T-configuration of a pneumatic three way ball valve can be used as a fluid diverting mechanism in which one inlet port is used to divert the fluid into two directions simultaneously. The L-configuration of a three-way pneumatic ball valve allows fluid diversion into one direction at a time. Using this configuration fluid can be directed into two different outlet ports. 

Figure: Three-way pneumatic ball valve.

Two-way pneumatic ball valve 

A two-way pneumatic ball valve has two ports that is the inlet and outlet ports. A two-way pneumatic ball valve has the inlet and outlet ports aligned in almost straight line which makes fluid flow straight from the piping system to the next pipeline via the valve. As such, two-way pneumatic ball valves are one-direction fluid flow valves as the fluid flows from the inlet going to the outlet only. Two-way pneumatic ball valves are the most common of all pneumatic ball valves. This is because these valves are simple in design and reliable for most applications. Two-way pneumatic ball valves are connected to the piping system in several styles such as using threads and bolts and nuts which makes them easy to disassemble for cleaning, repair, and maintenance. 

Figure:Two-way pneumatic ball valve

Reduced bore pneumatic ball valve 

This is a pneumatic actuated ball valve in which the valve ball has its inner diameter smaller than the inner diameter of the valve port. A reduced bore pneumatic ball valve introduces friction losses into the system due to the reduced bore diameter. However, these friction losses are comparatively small relative to the ones occurring in another valve types. Reduced bore pneumatic actuated ball valves are suited where there is turbulence, pressure drop, and where the material characteristic is not the main concern. Reduced bore pneumatic ball valves are small in size and have a lower cost. Reduced bore ball valve can be selected for use when the required flow rate is not strict because it will be cheaper and its weight is comparatively lower. 

Full bore pneumatic ball valve 

These are pneumatic actuated ball valves in which the ball bore diameter is the same as the pipe diameter. One of the main advantages of a full-bore pneumatic ball valve is that it has no additional friction losses and it is easier to clean. The ease of inspection and cleaning without the need to dismantle the valve and without halting production in large systems cannot be underestimated. One major challenge of a full port ball valve is that the cost is higher which is a drawback in many applications is. Full bore pneumatic ball valves are used in cases where low fluid flow resistance is important like on pump suction pipelines, where a pressure drop can affect the performance of the pump. 

Applications of pneumatic ball valves 

• Used in the gas and oil industries. 
• Food and beverages processing. 
• They are used in pharmaceutical applications. 
• These valves are used in steam power plants. 
• Pneumatic ball valves are used in chemical admixtures. 
• Mmany manufacturing industries for on/off applications.

Advantages of pneumatic ball valves 

• Operate quickly. 
• These valves employ a simple structure design, they are lightweight and are small in size. 
• Good seals that enhance zero leakage. 
• Easy to clean, do repair and maintenance. 
• These valves can be automated or semi-automated. 
• Versatile as they can be used in different applications in different industries. 
• Various types which help users to select the best valve considering cost and applications. 

Disadvantages of pneumatic ball valves 

• Pneumatic ball valves have cavities around the seat and ball which makes these valves not suitable for slurries as solid particles tend to cause valve blockage which increases opening/closing torque as well as valve failure. 
• Close and open quickly which can cause hammering and overpressures challenges. 

Troubleshooting pneumatic ball valves 

Fluid leaking from the ball seat 

• Damaged seat. Wash and flash the pneumatic ball valve. If seat is damaged, replace it. 
• Seating surfaces and balls not mating properly. Check the mating surfaces and adjust them accordingly. 

Body gasket leakage 

• Loose flange bolts and nuts. Tighten the bolts and nuts diagonally with equal torque. 
• Damaged gasket. Replace the gasket. 

Gland packing leakage 

• Loose gland packing connection. Tighten the connection. 
• Worn out gland packing. Replace the gland packing. 

Pneumatic actuator does not attain a complete open or closed position 

• The pressure is too low. Apply pressure as recommended by the pneumatic ball valve manufacturer. 
• Valve sizing is not correct. Check the pneumatic ball valve torque requirement with the actuator torque and use the recommended torque values. 
• Pinion not mounted in the correct position. Reassemble the pneumatic actuator accordingly. 
• Limit stop screws are set wrongly. Adjust the screws accordingly. 

Summary 

A pneumatic actuated ball valve is a valve that uses compressed air to open or close fluid flow. The pneumatic actuator has a piston, rack, and pinion which help to convert pressure energy into mechanical energy. It is the mechanical energy that is used to open or close the valve. When the pneumatic actuator receives pneumatic pressure, it causes the piston and rack to move linearly which makes the pinion rotate. When the pinion rotates, it rotates the valve stem and ball for 90^o. This helps to close/open fluid flow.

Pneumatic ball valves are designed with a ball having a hole at its center. Fluid flows through the valve via this hole. The pneumatic ball valve is open when the ball hole is in line with the pipe containing the fluid. When the valve ball hole is turned for 90^o making it perpendicular to the fluid flow, the valve is closed as no fluid can flow through it. Pneumatic ball valves are used in various applications such as food and beverages processing, pharmaceuticals, oil and gas industries, manufacturing industries, power plants among others. The advantages of pneumatic ball valves include ease of use, can be automated, can be used in various applications, can be cleaned and repaired, it operates quickly, and is versatility and durable.