A control valve is a valve that can be seen in many industrial applications, basically, it is a mechanical device that is capable to control the flow of liquid or gas through it. The control valve can start, stop, or regulate the movement of the liquid and gas through it.
Single and double-seated control valves
Single seated valve (single port valve)
The control valve construction is mostly like a globe, this control valve could be either, single-seated or double seated. A single-seated valve has a single seat and a single plug, in this type of valves the process pressure would reach on the bottom side of the plug and this will create a force upward in the valve stem. The actuator in this valve can control this force or it is capable to act against the force created by process pressure. So the actuator can move or hold the stem downward by controlling this force. The actuator in this valve must be able to control this force but it is a difficult task if the valve is big. If the valve is big then the created pressure will be big too and the actuator must be capable to handle this force, and because of this, the single-seated valve is not used for high-pressure applications. Single seated valves are suitable if we need a higher degree of shut off, single-seated valve or single-port valves are in many forms they are the globe, angle, bar stock, etc. The single-seated valve has top guided construction and it has good flow capacity than the top and the bottom guided valves. The selection of actuators and plugs for a single port valve must be done according to the pressure of the fluid.
What are the features of single-seated valves?
- These valves have a good flow capacity
- Tight shut-off
- Good rangeability
- Turndown is high and it is the ratio between the maximum and minimum controllable flow rate
What are the advantages and disadvantages of a single-seated valve?
- It provides high rangeability and tight shut-off
- A reversible plug is available
- A large actuator is needed
- Pressure recovery is low
- Only used for small diameter applications
- The force required to drive the stem is high
What are the applications of single-seated valves?
These valves are used to control a large range of process parameters and because of this feature, it is used in oil and gas production, power generation.
Double seated valve (double port valve)
A double-seated valve is a top and bottom guided valve and these valves have two plugs and two seats. In this type of valve, the line pressure acts upward in one plug and downward in the other, and because of this, the force is balanced. These valves are used for high-pressure applications. Double port valves are pressure balanced valves and they can close the valve plug against higher operating pressure. Tight shut off is not possible as in single-seated valves, these valves have fast flow response and greater capacity than single-seated valves and they are used when tight shut off is not needed. In this valve, the two ports cannot be opened at the same time. Double port valves can do the diversion of the flow from a single flow line to one or more outlets.
What are the features of a double-seated valve?
- A small force is needed to move the stem
- It can be used in large diameter applications
- Flow can be diverted
What are the advantages and disadvantages of a double-seated valve?
- It can be used for larger valves
- It can be used for high flow and high-pressure services
- Tight shut off is not possible
- Due to the erosion and cavitation, the body parts could wear out
What is the difference between a single-seated and double-seated valve?
Single seated valves are used in case of higher shut-off and the pressure range is low compared to a double-seated valve. Double seated valves are pressure balanced and can be used for high-pressure applications. It can’t do tight shut off and two ports can’t be opened at a time. These valves have a better flow response and good capacity.