In this article, we will learn all the basic details of a ball valve along with the definition, types, manufacturing, parts, working, applications, advantages, disadvantages, etc. Let’s explore ball valves:
What is Ball Valve? Definition
A ball valve is a flow control valve that operates by turning a ball inside it quarter turn along its axis. The turning motion of the ball controls the amount of liquid flowing through the valve.
Ball valve consists of a valve housing that houses a spherical-shaped ball inside it. The ball has a through bore in it to allow the flow of liquid from one side to another. The flow of liquid is therefore controlled by controlling the position of the ball with respect to the flow of liquid. When the bore of the ball aligns with the direction of flow, the valve is said to be in the open position and allows the liquid to flow through it. The flow is restricted when the axis of the bore is stationed perpendicular to the direction of flow.
The position of the ball is controlled using a handle provided on top. Turning the handle rotates the ball inside the ball housing thereby changing the position of the valve from open to close and vice versa.
Both the ball and the ball housing are made of stainless steel. A stem is passed through the housing from the top which connects the handle with the ball. A rectangular slot is provided on the top of the ball where the stem sits firmly. The other side of the stem is bolted to the handle.
Therefore, when the handle is turned, the stem turns the ball to allow or restrict the flow of fluid. Valve seats are generally made of Teflon in case of low temperature applications, but the material varies based on other types of applications. Sealing rings are further provided on valve seats to prevent leakage of liquid due to damage to the valve seat. Similarly, O-rings are provided on the valve stem to seal the gap between the valve stem and the valve body and prevent any leakage.
Types of Ball Valves in general
Float type ball valve
Fig 1: Floating type Ball Valve: Will be updated shortly
This is the most commonly used type of ball valve. Here the stainless steel ball is in a compressed position between two flexible valve seats and is held in contact with only a stem on top which controls the position of the ball. There are no supports on the bottom giving the effect that the ball is floating.
This type of ball valve is mainly used for low to medium pressure applications.
The valve seats are made of PTFE material. Thus, when the ball is in the closed position, fluid pressure acting on the ball forces it against the soft PTFE seats providing a solid seal against leakage.
Trunnion Mounted Ball Valve
Fig 2: Trunnion Mounted Ball Valve: Will be updated shortly
In this type, like the float type ball valve, a slot is provided on the top of the ball where the stem fits in. In addition to that a trunnion support is provided on the bottom of ball.
Hence due to additional support on the bottom, these types of valves are used also for high pressure applications.
The mechanical anchoring from the trunnion also absorbs the pressure from the line thrust. This in turn reduces the wear of the valve seat due to the extreme rubbing of the seat against the ball under the influence of high pressure when changing between open-close positions.
The trunnion also helps to reduce the operating torque required when the valve is used for high pressure applications. Thus, ease of operation, reduced valve seat wear, superior sealing, reduced operating torque are a few of the major advantages of trunnion mounted ball valves.
- Size:1-1/2 inch.
- Body & Ball Type:Full Port, Low Operation Torque,Temp Range:-60F to 450F
- The valve is fitted with PTFE seals for maximizing corrosion resistance and lifespan of the ball valve
- This ball valve is made of Stainless Steel 316 and has a plastic-covered lever handle for on/off manual control
- Nominal Working Pressure:1000 WOG:Max 1000 psi for Water, Oil, Gas. Fluid Medium:For use with liquids and gases
Types of Ball Valves based on flow control characteristics:
V port ball valve
V port valves have a ‘V’ shaped ball groove or a ‘V’ shaped valve seat that is precision machined which allows for desired flow rates of fluid between 0° to 90° of ball rotation. These valves provide close to linear flow characteristics and minimize pressure drop between inlet and outlet. Hence, these valves have higher flow coefficients compared to other valve types of similar size. Robust construction is provided to these types of valves due to their high flow velocity control capacity
Full bore ball valve
In full bore type, the area of the bore in the ball is equal to the internal diameter of the inlet flange. This allows for maximum rate of flow of fluid through the valve as all the fluid that enters through the inlet flange passes at the same rate through the ball limiting the drop in pressure.
Full bore type valves are mainly used for pipelines used for the transfer of viscous fluids as this type of valve provides almost negligible flow resistance.
Reduced bore valve type
In reduced bore type of ball valve, the area of the bore in the ball is smaller compared to the internal diameter of the inlet flange. This results in a reduction in the rate of flow of fluid through the ball. Reduction in flow causes increased pressure difference between fluid at inlet and outlet of the ball valve. It also increases the resistance to the flow of fluid.
Reduced bore valve types are however lighter in weight and are smaller in size requiring lesser space and are most suitable for pipelines transferring gas and fluids having similar physical properties to water.
Types of Ball Valves based on design
Split type ball valves are valves manufactured in 2 or 3 parts and then connected together using nuts and bolts or threaded joints. Each part is manufactured individually of steel by the process of casting or forging. Casting is generally used to manufacture more complex split valve designs.
For higher pressure applications, split type ball valves are manufactured by the process of forging. Forged split valves are also used for pipelines transferring corrosive and acidic fluids. Split type valves are further divided into 2 piece split valves and 3 piece split valves.
In 2 piece split valves, the valve housing and inlet flange is constructed as one single unit and the outlet flange as the other unit. In 3 piece split valves, the valve housing, the inlet flange and the outlet flange are all manufactured as 3 different units.
Advantages of split type ball valves include ease of maintenance as each component is separately manufactured and connected. Also, there is no need to replace the entire ball valve assembly if there is any kind of external damage. That individual unit can only be replaced.
Multiple port ball valves refer to ball valves with more than 2 ports (i.e. inlet and outlet). This allows for better connectivity between pipelines transferring the same fluid. Generally used multiple ports ball valve are 3 way and 4 way ball valve. In 3 way ball valve fluid can flow in 3 directions. It allows to shut or open flow in any direction making the fluid flow in the desired direction.
3 way ball valves are available in 2 configurations, L and T configuration.
Fig 3: L Configuration: Will be updated shortly
Fig 4: T Configuration: Will be updated shortly
Fig 3&4 ref: : Will be updated shortly
In 4 way type, fluid is allowed to flow in 4 directions. They are normally used for X configuration
Fig 5: X Configuration: Will be updated shortly
Types of valves based on the method of actuation:
Pneumatic actuators use the pressure energy of air to produce mechanical motion of the valve. The actuator consists of a piston cylinder arrangement. Compressed air acts on the piston to produce a linear motion between the two dead centers. The piston could be double acting or single acting.
In case of double acting piston, air is entirely responsible for the to and fro motion and in case of a single acting spring force is used along with compressed air.
Fig 6: Pneumatic piston: Will be updated shortly
To convert the linear motion of the pneumatic piston a rack and pinion arrangement is used. The rack is connected to the piston rod of the piston. The pinion is fixed onto the valve stem of the ball valve.
Now, as the air acts on the piston, the piston along with the piston rod moves and as a result of that, the rack also moves. The pinion is engaged with the teeth on the rack which results in rotational motion of the pinion. Since the pinion is fixed on the valve stem, the stem also rotates along with the pinion there by opening the valve.
Solenoid valves are used to regulate air supply to the pneumatic piston. Electrical signals from the control unit are communicated to the solenoid valves according to which it supplies air to the actuator.
Electrical actuators use electrical motors to convert electrical energy into mechanical motion of the valve. The motor could be AC or DC powered. The shaft of the motor is coupled with the stem of the valve. As the motor turns, the valve stem also rotates thereby opening the valve.
To compensate for the high torque requirements to open and close large size ball valves, gear arrangements are used. The shaft of the motor is coupled to the valve stem via a series of gears to multiply the torque produced.
Electrical actuators, unlike its pneumatic counterpart is used for accurate positioning of the valve anywhere between 0° to 90° of valve rotation. This way flow rate of fluid through the valve can be effectively controlled. Limit switches are used to cut off current to the motor when the valve reaches full close and fully open position.
Fire safety types:
Fig 7: Fire Safety Valve: Will be updated shortly
In case of fire in the vicinity of a ball valve, the heat causes the PTFE valve seat to melt. This results in the valve to start leaking and this might aggravate the hazard created by fire.
Fire safety type valves thus contain an additional metallic seat that comes into action as soon as the PTFE seat fails thus preserving the integrity of the valve. As seen in the diagram, as the PTFE seat fails, the metallic seat automatically comes in contact with the ball. Certain designs of fire safety valves utilize spring force to put metallic seats in action.
Manufacturing Process for Ball Valves
Forging is one of the oldest manufacturing methods known to man and has been used extensively for valve manufacturing. Forging is a process in which metal is heated up to its recrystallization temperature and then subjected to compressive forces to give desired shape to the metal. The compressive forces are given using hammers or in this case hydraulic presses. For stainless steel forging, Chromium dies are fixed to the hydraulic presses which then apply tons of amount of forces on to the metal.
Dies used can be open or closed type. Open dies produce parts close to the desired accuracy. Machining of parts is then required largely to eliminate the discrepancies. Closed dies produce parts to much higher accuracy and require very little machining once forging is completed. This type of die can therefore be used to produce complex parts.
The process of forging develops a refined grain structure for the metal. This provides the metal with reduced hardness and increased strength. The valves manufactured by forging can then be used for high temperature and pressure applications. Also, the defects produced in this type of manufacturing is comparatively lower.
In casting, the metal is heated up to its melting point after which the molten metal is poured into a mold. A mold is basically a cavity of the desired shape of the component. Once the molten metal solidifies, the mold is separated, and the molten metal permanently takes the shape of the mold. For the purpose of manufacturing valves, stainless steel and carbon steel are used.
Carbon is added to steel to give it properties like hardness, wear resistance and better surface finish. So based on the amount of carbon, carbon steels are further classified as low carbon steels, medium carbon steels and high carbon steels.
After the casting is completed, heat treatment is carried out on the cast which includes the following:
- Annealing: The cast is heated to a specific temperature and held at that point for some time before allowing it to cool slowly.
- Normalizing: Here again, the cast is heated to a specific temperature and allowed to cool under open air or fan.
- Quenching: In quenching, the cast is cooled at a much more rapid rate by immersing the cast in water or oil.
The products manufactured by casting have excellent dimensional accuracy and require little to no machining. However, casted products are prone to certain defects if the processes are not carried out properly.
The defect mainly includes,
- Porosity: This is air or gas trapped inside the cast that has failed to escape. This reduces the strength of the cast and can lead to failure.
- Slag inclusion: This is the deposition of foreign particles into the cast. It could be debris, sand, etc.
The defects are identified during the testing process where destructive and non-destructive techniques are employed.
Troubleshooting of Ball Valve
Valve does not hold i.e., valve is leaking
|The ball surface is worn out||Replace the ball and perform lapping|
|Wear down of seat or damaged seat||Replace the seat and perform lapping|
|Valve is not in closed position||Overhaul the valve, check for conditions of ball and seat and for any kind of obstruction like dirt between valve and seat.|
Leakage from valve stem
|Stem nut loose||Tighten stem nut|
|Damaged or bent valve stem||Replace damaged stem with a new one|
|Valve stem seals damaged||Replace valve stem seals with new ones|
Opening and closing torque too high
|Dirt accumulation between ball and seat hampering movement of ball||Try flushing the valve by opening and closing the valve. If that does not work, then disassemble the valve and clear the obstruction.|
|Damaged ball or valve seat||Perform lapping of ball and seat or replace both with new one.|
|Excessive amount of fluid pressure acting on the valve.||Check if the fluid parameters are normal|
Leakage from valve body
|Gaskets are damaged||Replace gaskets with new ones|
|Excessive pressure or temperature of fluid flowing||Check the parameters of the fluid.|
Valve fails to move after giving electrical input
|No power supply.||Make sure power is supplied to electrical actuator.|
|Solenoid valve faulty||Replace Solenoid valve|
Valve fails to move after giving pneumatic input
|Compressed air pressure low||Make sure the air reservoir supplying compressed air has pressurized and air compressor is running.|
|Compressed air leaking||Perform leak test on the line to identify point of leakage and rectify it.|
|Pneumatic piston stuck due to debris or rust particles.||Replace the pneumatic actuating unit and drain air reservoirs from time to time to remove accumulated moisture and dirt.|
Difference between ball valve and gate valve
Globe valve consists of a valve disk resting on top of valve seat. The valve disk is connected to a wheel via a spindle. As we turn the wheel, the valve disk lifts from top of valve seat thus allowing the flow of liquid. Ball valve as explained earlier consists of a rotating ball connected to a handle via a stem. As the handle is turned, the ball rotates as allows the liquid to flow through the bore in the ball.
A major advantage of globe valve is that is allows for throttling of flow of liquid. Ball valve is strictly for open and close operation and cannot be used for throttling of liquid flow without damaging the ball or the valve seats. Globe valves require several turns of wheel to open or close the valve. Ball valves can be quickly opened and closed by just 90° turn of handle.
For globe valves, we have non return type which do not allow for backward flow of liquid. Ball valves do not have non return type. Maintenance of globe valve can be carried at the location of the valve itself without separating the valve from the flanges. Ball valves however cannot be overhauled at the location and needs to be separated from the pipeline.
Globe valves are comparatively heavier and larger in size to ball valves. Globe valves however also have a non rising stem type which allows it to be used in restricted space.
Advantages fo Ball Valve
- Ball valves are compact and light weight compared to other types of valves like gate valve and hence put a lesser load on the pipelines.
- Easy maintenance and low lubrication requirement.
- Allows for quick closing of valve.
- Ball valves although light and compact can be used in high pressure and temperature applications.
- Ball valves possess excellent sealing capabilities making it suitable to use for various mediums.
- Ball valves are more affordable compared to other types of valves.
Disadvantages of Ball Valve
- Due to the presence of abrasives in the fluid, the valve seats are prone to wear down. The valve is also prone to get jammed due to suspended particles being trapped and causing an obstruction.
- Ball valves can be used only for temporary throttling. Permanent throttling requires specially designed ball valves.
Applications of Ball Valves
Ball valve due to its flow and pressure control properties finds its industrial use in mainly the oil and gas industry. They also find applications in residential and chemical storage facilities as well as in the food industry which includes milk and dairy, bread, and baked goods.