Control valves are a vital part of many industrial processes. While they all serve the same basic function, hydraulic control, the methods and modes of control are vastly different.
What is a Control Valve?
A control valve regulates the flow, pressure, and temperature of fluids that flow through a pipeline. A plant may have hundreds of control valves, all serving the process with very specific task of keeping the system running within an acceptable operating range. Valves are more than simple on/off mechanisms as they are designed to move to an infinite number of median positions between on and off which allows for flow and pressure control.
What Is Their Purpose?
The basic requirements of a control valve depends on their ability to perform specific functions:
- Ability to throttle or control the rate of flow
- Lack of turbulence or resistance to flow when totally open
- Rapid response to opening and closing
- Tight shut off – no leaks
- Ability to allow flow in one direction – preventing backflow
- Opening at a pre-set pressure
- Ability to handle corrosive or abrasive fluids
How a control valve is selected depends on service conditions. This is the environment, the task, and the load they will be required to handle. Experienced engineers can evaluate the need and select the right valve.
Types of Control Valves
There is no single valve type that can handle all applications. Valves can broadly be categorized depending on stem movement which is either linear or rotary.
Linear Motion
Gate Valve
- Characteristics: Gate valves use a sliding gate mechanism that is moved by the stem to either an on or off position. It sits perpendicular to direction flow.
- Application: Suitable for high temperatures and high pressures with a variety of fluids.
- Advantages: Tight sealing, low pressure drop when fully open.
- Disadvantages: May cause vibration. Requires a large actuating force and some models have a slow response time. Not intended for viscous liquids or slurries. Not for regulating flow.
Globe Valve
- Characteristics: Globe valves use a disc or plug that is moved off of a seat with an opening that is proportional to the travel of the plug.
- Application: Used primarily for throttling purpose due to large seating capacity and high/flow controllability. Suitable for high temperatures and general purpose flow control.
- Advantages: Globe valves have the most reliable form of seating and the flow can be controlled to any desired degree.
- Disadvantages: In partial open conditions the seat can wear.
Diaphragm Valves
- Characteristics: A flexible diaphragm is connected to a support known as a compressor. When open, the diaphragm is lifted out of the flow path for a smooth, streamlined flow. When closed the diaphragm is seated in the body against a structure known as a weir.
- Application: Diaphragm valves are used for corrosive liquids that are at a low temperature and flowing at a low pressure.
- Advantages: The diaphragm isolates the working parts of the valve against the corrosive material flowing through it.
- Disadvantages: Not intended for high temperatures or high pressure.
Pinch Valve
- Characteristics: A pinch valve is a simple design. A pinching mechanism regulates flow which creates minimal turbulence and friction.
- Application: They are a practical solution for on/off or proportional flow control of many abrasive and corrosive products including powders, slurries, aggregates and chemicals.
- Advantages: Inexpensive and can create a tight seal when closed. Easy maintenance.
- Disadvantages: They have a limited temperature range and pressure limit.
Rotary Motion
Ball Valve
- Characteristics: A ball valve is a ported sphere in a housing that is rotated to control flow. The housing is typically PTFE which is chemically inert and durable.
- Application: Ball valves are used for flow control of corrosive liquids and slurries that are under high pressures and temperatures.
- Advantages:Ball valves are easy to maintain, lightweight, and can be installed in compact areas.
- Disadvantages: The PTFE seats are subject to extrusion under very high pressures. Also the ball can retain some liquid material when completely closed, which can lead to corrosion or contamination.
Butterfly Valves
- Characteristics: These rotary valves have a disk that rotates to right angles within the pipe section. Rotating the stem opens the disk to close off the pipe like opening the wings of a butterfly.
- Application: Butterfly valves are used in large flow applications or operations where leakage is unimportant.
- Advantages: Simple to use and compact enough for tight areas. Low weights and costs translate to good flow control.
- Disadvantages: No tight shut off means the valve can leak under increased pressures.
Plug Valve
- Characteristics: A tapered or cylindrical plug is raised or lowered through a seat. The bore in the plug connects the inlet and outlet ends of the valve providing straight line flow. Very reliable in most applications.
- Application: Plug valves are used in the petrochemical industry for general on/off services.
- Advantages: Available in a wide range of materials, they provide tight shut off, quick opening, and low pressure drop.
- Disadvantages: Tend to have a higher cost compared to ball valves.
How To Choose a Control Valve
The experienced engineers at Pioneer Industrial will work to understand how your facility works so that you can make the best possible choice when you are installing new control valves or if you are replacing worn valves as part of an existing system. It is important to choose the valve not at a single normal operating point, but to take all possible process conditions into account. Selection of the type and size of the valve depends heavily on minimum, normal, and maximum process conditions. Pioneer can help you determine the correct valve and actuator package needed for almost any application.
Pioneer Industrial and Masonelian Control Valves
At Pioneer Industrial, we believe in doing the job right the first time because in our experience, mistakes and delays are not only frustrating, they are costly in time and resources. This is why we exclusively use Baker Hughes Masonelian products for any control valve installation project. We can work with any brand of valve and are happy to accommodate them, but when an application calls for a reliable, high-quality product, we turn to Masonelian.
Reach out to Pioneer today to learn more about your control valves, schedule an inspection, or find out how we can improve your systems and get the most out of your equipment. We are ready to assist you throughout the life of your valves to make sure they are performing at the highest level.
