A Single seated valve has one trim and one seat, while a double-seated valve has two trims and two seats. A single seated valve is used for low-pressure applications. on the other hand, the double-seated valve is best suited for high-pressure applications.
In a process, there can be a need to regulate the flow for getting the desired output. For this, valves are used. The valves that control flow are called control valves.
Control valves are valves that find applications in industries. The control valve is basically a mechanical device that is capable of controlling the flow of liquid or gas through it. Control valves are able to start, stop and/or regulate the movement of the liquid and gas through it. The control valve is generally a globe valve. This control valve can be a single-seated or double-seated valve.
Single seated control valve
Single-seated valves are also called single-port valves. The single-seated valve will have a single seat and single plug. In these types of valves, the process pressure will reach the bottom side of the plug. This creates an upward force in the valve stem. In the valve, the actuator would control this force or else it will be capable of acting against the force created by process pressure.
The actuator can move or hold the stem downward by controlling a force. Actuators in these types of valves must be able to control this force. This is a difficult task if the valve is big in size. When the size of the valve is big, then the created pressure is also larger. So, the actuator should be capable of handling this force. Due to this reason, single-seated valves are not used in high-pressure applications.
Single seated control valves are suited when a higher degree of shut-off is needed. Single seated control valves are available in many forms like the globe, angle, bar stock, etc. the single seated valves or the single port valves have top-guided construction and have a good flow capacity as compared to the top and bottom guided valves.
The selection of actuators and plugs in a single port valve should be done according to the pressure of the fluid. The single-seated control valves have the following features:
- Single-seated control valves have good flow capacity.
- Single-seated control valves have tight shut-off.
- Single seated control valves have good range ability.
- Single-seated control valves have a higher turndown. Turndown is the ratio between the maximum and minimum controllable flow rate.
The single seated valves have some advantages and disadvantages.
Advantages of Single-Seated Valve
- Single seated control valves provide high-range ability.
- Single-seated control valves have tightly shut-off.
- In Single seated control valves a reversible plug is available.
Disadvantages of Single-Seated Valve
- A single seated control valve needs a large actuator.
- The pressure recovery is low in Single seated control valves.
- Single-seated control valves are only used for small-diameter applications.
- The force required to drive the valve stem is high in the Single seated control valve.
The single-seated valves are used to control a large range of process parameters. Due to this feature, Single seated control valves are used in oil and gas production and power generation.
Double-seated control valve
Double-seated control valves are also called double-port valves. The double-seated control valves are top and bottom-guided valves. Double-seated valves have two plugs and two seats. Double-seated control valves have a line pressure that will act in the upward direction of one plug. In the other plug, it will act in a downward direction. Due to this, the force remains balanced.
Double-seated control valves are used in high-pressure applications. Double-seated control valves are pressure-balanced valves. Double-seated control valves also can close the valve plug against higher operating pressure. Unlike the single-seated control valves, in double-seated control valves, tight shut-off is not possible.
Double-seated control valves have a fast flow response. The Double seated control valves also have a greater capacity as compared to single-seated valves. Double-seated control valves or double port valves are used when a tight shut-off is not needed.
In double-seated control valves, the two ports cannot be opened at the same time. Double-seated valves are used to divert the flow from a single flow line to one or more outlets. The double-seated control valves have the following features:
- Double-seated control valves need less amount of force to move the stem.
- Double-seated control valves may be used in large-diameter applications
- By using double-seated control valves, the flow can be diverted.
The double-seated valves have some advantages and disadvantages.
Advantages of Double-Seated Valve
- Double-seated valves can be used for larger valves.
- Double-seated control valves can also be used for high-flow and high-pressure services.
Disadvantages of Double-Seated Valve
- In double-seated control valves, tight shut-off is not possible.
- In double-seated control valves, the body parts could wear out due to erosion and cavitation.
Difference between the single seated control valve and double seated control valve
| SINGLE SEATED CONTROL VALVE | DOUBLE-SEATED CONTROL VALVE |
| Single-seated control valves have only one plug and one seat. | Double-seated control valves have two plugs and two seats. |
| Single seated control valves have slight leakage. Tight shutoff is also achievable. | Double-seated control valves have a large leakage. |
| Single seated control valves allow small differential pressure. | Double-seated control valves are subjected to small unbalance forces and allow large differential pressure. |
| Single-seated control valves have a small flow capacity. | Double-seated control valves have a large flow capacity. |
| Single seated control valves are smaller in size. | Double-seated control valves are larger in size. |
| Due to the large thrust of the fluid medium to the valve trim, so, the unbalanced force is higher. Hence, single-seated valves are not used when the application has a high-pressure difference and large diameter. | Double-seated control valves have complex flow paths. So, they are suitable for the control of fiber-containing media and high-viscosity fluids. |
