OS&Y Valve 

What is OS&Y valve? 

OS&Y valve means outside screw and yoke or outside stem and yoke valve. OS&Y valve is a type of gate valve. OS&Y valve works by using a gate that closes and opens fluid flow through the valve. OS&Y gate valve manufacturers designs working principle is lower or raise the gate to close and open fluid flow respectively. When an OS&Y valve is fully open, the valve does not have any obstruction in the fluid flow path. This results in very low fluid friction thus making the valve’s efficiency high. In OS&Y valve, when the stem is rotated it moves out or into the valve which then makes the gate opens or closes the valve. OS&Y valve is a type of rising stem gate valve. This type of valve can be operated manually or using actuators. Some of the actuators that can be used on OS&Y valve are pneumatic, hydraulic and electric actuators.

Figure: OS&Y valve.

Components of an OS&Y valve 

Valve body 

This is the component of an OS&Y valve that is used as the main pressure boundary. The valve body in an OS&Y valve is the main component as it is the framework that holds all the other components together. The valve body is the first pressure boundary of an OS&Y valve which resists pressure loads from the connected pipes. The valve body of an OS&Y valve has the inlet and outlet ports through which the valve is connected to the pipeline through welding, bolts, or threads. 

Trim 

OS&Y valve manufacturers refer to trim as the internal components such as gate, sleeves, and stem.

Seat 

An OS&Y valve has two seats. The two seats are used to provide a reliable seal with the gate. The valve seats are in form of seat rings or integrated with the body. In an OS&Y valve with seat rings, these rings are pressed into or threaded into position and welded into the body. Seats that are integrated into the body are of the same material as the body while those that are threaded in or pressed into the body can be different from the body material. 

Stem 

A stem is the component of an OS&Y valve that is used to lift and lower the gate to allow fluid flow or block fluid flow. The stem connects the handwheel or actuator to the gate. 

Bonnet 

This is the component of an OS&Y valve that is used to protect internal parts of the valve. The bonnet is connected to the valve body of an OS&Y valve using bolts or screws to form a leakage-proof seal. This makes it possible to do repair and maintenance in an OS&Y valve since the bonnet can be removed when it is necessary.

Valve actuator 

An actuator in an OS&Y valve is used to operate the stem and gate to open or close the fluid flow. The actuator can be operated manually using a handwheel or manual lever. For automatic OS&Y valve, the actuators that can be used are electric, pneumatic, or hydraulic actuators. 

Packing 

Packing refers to fibrous material or other compounds used provide seal between internal parts of the OS&Y valve and outside of the valve stem. OS&Y valve manufacturers mostly use materials like Teflon to make packing. Packing in an OS&Y valve needs to be compressed properly to prevent fluid leakage and damage to the stem. 

Figure: Components of an OS&Y valve.

How does an OS&Y valve work? 

OS&Y valve operates by raising and lowering gate to open and close fluid flow respectively. The valve operates by using a handwheel or by using an actuator. When the handwheel is rotated it rotates the valve stem. The direction of rotation of the handwheel determines if the valve will open or close. To open an OS&Y valve, the valve operator rotates the handwheel in the anticlockwise direction which makes the stem rotate in the same anticlockwise direction while it is moving upwards. When the stem is raised it simultaneously raises the gate which allows fluid to flow. To close the OS&Y gate valve, the handwheel is rotated in the clockwise direction which makes the stem rotate in the same anticlockwise direction. This makes the gate that is connected to the stem move downwards and thus block fluid flow. When the OS&Y valve is opened, the stem protrudes above the handle or handwheel. When the OS&Y valve is closed, the stem does not protrude above the handle/handwheel. This makes it easier to notice when an OS &Y valve is in an open or closed state. 

Figure: Working of an OS&Y valve in closed and open state.

Types of OS&Y valves

OS&Y valve with solid wedge gate 

This is one of the most common and widely used gates in an OS&Y valve. The reason this type of valve is preferred is because of its high strength and simple design. Installation of an OS&Y valve with solid wedge gate can be in any position and it is best suitable for use in almost all fluids as well as in turbulent fluid flows. One of the major challenges associated with OS&Y valves with solid wedge gates is that they cannot compensate for changes in valve seat alignment because of pipe thermal expansion. This design makes an OS&Y valve with a solid wedge vulnerable to fluid leakage. If OS&Y valve manufacturer designs the valve to be used in high temperature application, it is designed with a thermal locking mechanism. Thermal locking is a case whereby the wedge gate gets stuck between valve seats because of expansion. This makes OS&Y valves with solid wedge gates suitable for use only in the medium to low temperature-pressure applications. 

Figure: OS&Y valve solid wedge gate.

OS&Y valve with flexible wedge gate 

This is an OS&Y valve that has a flexible wedge gate that has a cut around its perimeter. The cuts vary in depth, size, and shape. An OS&Y valve with a narrow, shallow cut on the wedge perimeter results in less flexibility but it has high strength. A wider and deeper cut on the gate of an OS&Y valve gives more flexibility but it lowers the strength. OS&Y valve manufacturers design this valve aiming to enhance seat alignment and tight seal with zero leakage. Also, this type of OS&Y valve has better performance in the case of thermal binding. As such OS&Y gate valves with flexible wedge gates are used in steam applications. Steam line thermal expansion sometimes causes valve body distortion which can cause thermal blinding. With a flexible wedge gate in an OS&Y valve, the gate can flex as the seat compresses because of thermal expansion emanating from the steam pipeline and hindering thermal blinding. The major challenge associated with OS&Y valve with a flexible wedge gate is that fluid tends to collect in the gate which can cause corrosion and make the gate weak. 

Figure: OS&Y valve with a flexible wedge gate.

OS&Y valve with a parallel slide gate

This is an OS&Y valve that does not experience wedge action. This type of OS&Y valve closes by using two gates connected using a gate holder. This OS&Y valve has springs that move downwards in parallel to block fluid flow. When the body port is sealed, the stem prevents further movement. When the OS&Y valve with parallel slide gate is opened, the gate moves upwards and the stem sits back. 

Applications of OS&Y valves 

• Control media that has slurries. OS&Y valves can use their gates to easily cut through the slurry allowing the valve to close. 
• Used in viscous fluid such as oils and grease. 
• Control of water supply. 
• Used in the gas and oil industries. 
• Pharmaceutical applications. 
• Chemical applications. 
• Irrigation systems where the speed of closing is not very essential relative to the strength needed to support high pressure and high flow rate. 

Advantages of OS&Y valves 

• Low-pressure loss when closing or opening. 
• They can work in slurry applications. 
• Can be used in high-pressure and high-temperature applications. 
• Easy to repair. 
• These valves are versatile as they can be used in different industrial applications. 
• Bi-directional valves.
• Provide perfect shut-off because the contact between the seat and the gate extends over the whole circumference. 

Disadvantages of OS&Y valves 

• Cannot close and open fast like other valves such as ball valve. 
• These valves need a large area for installation, maintenance, and operation. 
• Require a large magnitude of torque due to high pressure across the seats. 
• Not suitable for throttling applications. 

Troubleshooting OS&Y valves 

OS&Y valve not giving the correct number of turns when it is closed. 

• Debris in the seating area. Create flow through the OS&Y valve by opening the downstream hydrant to help remove the debris. 

The closing/opening nut keeps rotating after you have attained the correct number of turns 

• Excess torque has been applied to the opening/closing nut which caused damage to the stem nut or stem. Disassemble the OS&Y valve to check if the stem or stem nut is damaged and replace it as necessary. 

Fluid leakage between the body and the bonnet 

• OS&Y valve has its damaged gasket O-rings. Replace the gasket O-ring.
• Bonnet bolts are loose. Tighten the bolts and nuts using the recommended torque by the OS&Y valve manufacturer.
• Bonnet or body flanges are damaged. Replace them as necessary. 

OS&Y valve has leakage through the stuffing box area 

• Damaged stuffing box packing. Replace the stuffing box packing and stem O-rings. 

Summary 

OS&Y valve is a type of gate valve that has a rising stem. The valve operates by use of a gate component which is lowered or raised by the valve stem to close or open fluid flow respectively. OS&Y valve is used for on/off fluid flow applications but not suitable for throttling applications. When the valve is open, the stem raises above the handwheel. When it is closed, the stem does not protrude above the handwheel. This feature helps the valve operator to know when an OS&Y valve is in a closed or open state. OS&Y valve manufacturers produce manual or actuated valves.

There are various types of OS&Y valves which include OS&Y valve with solid wedge gate, OS&Y valve with flexible wedge gate, and OS&Y valve with parallel slide gate among others. These valves are used in various applications such as oil and gas, slurries, pharmaceuticals, chemicals, water supply, and irrigation systems among others. The advantages are versatile, leakage-proof, high strength, repairable, bi-directional fluid flow, and low-pressure loss. However, OS&Y valves open and close slowly, they need large area for installation, operation, and maintenance, and not suitable for throttling applications.