What is a rising stem ball valve?
The rising stem ball valve is a type of ball valve with a long stem that rises above the body of the valve. A rising stem ball valve is used for on and off fluid flow applications. Rising stem ball valves are mostly all-metal and fireproof. Rising stem ball valves have wide range of temperatures of around -200oC and 815oC. Rising stem ball valves are designed such that movement of ball and seat does not create friction and the valve needs small torque to open and close. Rising stem ball valves are suitable for applications that need zero fluid leakage and which are subject to frequent operation. Rising stem ball valves are used in critical isolation of different applications. These valves are used in various applications such as water, acids, solvents, and natural gas among others. These valves use a tilt-and-turn principle which removes rubbing. Rubbing is the main cause of wear and valve failure in most ball valves. Rising stem ball valves do not have seal rubbing when opening and closing which makes last longer.
Figure: Risings stem ball valve.
Components of a rising stem ball valve
There are various parts of a rising stem ball valve. Among the main parts include the following.
Handwheel/actuator
The handwheel is used in manual rising stem ball valves and it is where the valve operator applies torque to open/close the valve. When the orbit valve is automated it uses an actuator that provides torque to the ball to open/close the valve.
Body/housing
The body is also known as valve housing and it is the component of a rising stem ball valve used to provide cover to all internal parts of the valve.
Bonnet
Bonnet is a component that is placed on top of the valve body to provide cover to the internal parts of the valve. The bonnet is connected to the body using bolts and nuts.
Stem
A stem is the component of a rising stem ball valve that is used to connect the handwheel or actuator to the ball. The stem transmits torque from the actuator or handwheel to the ball so that it can open or close.
Ball
The ball is also known as the valve core. The ball has a hole at its center where fluid flows through.
Seat
This is a component placed between the ball and the body to prevent fluid leakage and support the ball.
Figure: Components of a rising stem ball valve.
How does a rising stem ball valve work?
The rising stem ball valve works by using a rotating motion as well as cam action to produce a perfect seal. The rising stem ball valve works by turning the handwheel several times for manual valves. To open the rising stem ball valve, the handwheel is rotated several turns. This makes the ball bore turn and become in line with the pipeline and then fluid starts flowing. To close the rising stem ball valve, the handwheel is rotated clockwise or the actuator rotates the stem for actuated ball valves. The rotation of the stem rotates the ball in the clockwise direction which makes the ball bore become perpendicular to the pipeline. In this case, the fluid cannot flow through the valve as it is blocked by the ball. The ball in a rising stem ball valve is held in a place away from the seat using the valve stem which helps to eliminate abrasion and makes the valve to use small torque to open/close relative to other ball valves.
Types of rising stem ball valve
Side entry rising stem ball valve
Side entry rising stem ball valves are valves that have two or three pieces of the body. The pieces of a side entry rising stem ball valves are assembled from their sides using bolts and nuts. Each piece of a side entry rising stem ball valve is made using forging method. The forging method helps to eliminate defects associated with valves made through casting method. One of the main advantages of a side entry ball valve is that it is easy to assemble and that the internal components can be easily aligned. Also, side entry rising stem ball valves can be inspected, cleaned, and repaired.
Figure: Side entry rising stem ball valve.
Top entry rising stem ball valve
This is a rising stem ball valve that is assembled from the top side of the valve. In this rising stem ball valve, the valve operator can access the valve seats and ball easily from the top side during repair and maintenance without removing the valve from the pipeline. Top entry rising stem ball valves are made through casting method. This makes the valve undergo non-destructive tests to ensure it has no casting defect which can cause leakage when the valve is in use. The top entry ball valve has two pieces one at the bottom and another one at the top. The two pieces are held together using bolts and nuts which makes these valves easy to dismantle for repairs, cleaning, and inspection.
Figure: Top entry rising stem ball valve.
Manual rising stem ball valve
These are rising stem ball valves that are operated using a handwheel. As the name suggests, manual rising stem ball valves need the valve operator to be around every time the valve needs to be opened/closed. The valve operator applies torque on the handwheel to open/close the valve. When the handwheel of a rising stem ball valve is rotated in the anticlockwise direction it turns the valve on. When the manual rising stem ball valve handwheel is rotated in the clockwise direction it closes the valve. Closing and opening directions are indicated on the handwheel. One advantage of a manual rising stem ball valve is that it can also be automated if the user finds it necessary. Also, manual rising stem ball valves are cheaper compared to automatic counterparts.
Actuated rising stem ball valve
This is a rising stem ball valve that is operated using an actuator. The work of the actuator is to provide the torque required to open or close the rising stem ball valve. The actuator provides rotary motion to the ball valve causing its opening/closing operation. Actuated rising stem ball valves can be fully automated or semi-automated. One advantage of an actuated ball valve is that it can work without a valve operator. Rising stem ball valves with actuators are suitable where the torque required to open the valve is very high. However, actuated rising stem ball valves are expensive unlike their manual counterparts. The actuators that can be used in rising stem ball valves are hydraulic, pneumatic, and electric actuators.
Features of a rising stem ball valve
Rising stem ball valves are anti-abrasion
The ball surface is hardened which helps to meet seal performance even in severe media.
Mechanical wedge force
Rising stem ball valves have a cam bevel at the lower end of the valve stem meant to provide wedge force for keeping the seat and ball tight.
Dual stem guides
Rising stem ball valves are designed with stem guide grooves to slide along a rigid guide pin to control the lifting of the stem and rotate smoothly.
Self-cleaning
Rising stem ball valves are such that when the ball deviates from the seat, the fluid flows 360o degrees along the sealing surface which helps to rinse impurities.
No wear in rising stem ball valve
The design of a rising stem is such that the ball rotates away from the seat. This helps to eliminate friction between the ball and seat common in other ball valves.
Small operating torque
The rising stem ball valve employs a design that makes the sealing surface free from friction which reduces the torque needed to open and close the valve.
Applications of rising stem ball valves
Advantages of rising steam ball valves
Disadvantages of rising stem ball valves
Troubleshooting rising stem ball valves
Leakage through valve connections
Rising stem ball valve experiencing leakage through the seat
Leakage through the ball
The rising stem ball valve is hard to rotate
Noisy operation or water hammer
Summary
A rising stem ball valve is a type of ball valve. The rising stem has a long stem rising above the valve body. Rising stem ball valve is an on/off ball valve. This valve can be used in a wide range of temperatures ranging between -200 oC and 815 oC. Rising stem ball valve manufacturers design the valve such that the ball and seat do not rub each other making them free from abrasion wear. As such, rising stem ball valves need low torque to open or close relative to other ball valves. Rising stem ball valves are made of strong metallic materials to help them mechanically strong and resistant to high temperatures. Some of the rising stem ball valve types include manual rising stem ball valves, actuated rising stem ball valves, top entry rising stem ball valves, and side entry rising stem ball valves. Rising stem ball valves are used in different applications such as petroleum, natural gas, chemical industries, paper, and pulp industries, and steam power generation industries among others. Advantages of rising stem ball valves include self-cleaning, quick to open/close, versatile, durable, low torque operation, they can be cleaned, inspected, and repaired while in the field, abrasion-free and very strong. However, rising stem ball valves are expensive and they can only be installed in a vertical position. Nevertheless, the advantages and special features of rising stem ball valves outweigh the few disadvantages by great margin.
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