Valves are fittings that regulate and direct the flow of fluids from higher to lower-pressure environments in a pipeline by fully or partially opening or closing routes. This is used for opening or closing a system, to manage the rate of flow, as well as to allow for maintenance and repairs. Valves used in pipe system solutions come in a variety of materials, shapes, and sizes. Depending on their function, different types of valves are used. These include gate, globe, ball, butterfly, and check valves.
Valves: An introduction
Description of Valve Parts
Pressure-containing parts: Body, bonnet, stud, and nut
Wetted parts: Body, shaft, seat, and closure
Other: Yoke, end connection, operator
Choosing the Right Valve
In order to select a valve, you will need to determine its function. That is, will it be used to regulate fluid dynamics or to stop their flow? The next consideration is for the type of media that the valve is handling. This can range from gas to liquid, and from corrosive to chemically neutral. The medium handled can come in a wide range of viscosity, and may contain particles that can clog a valve’s operations. Choosing a valve is also dependent on the nominal diameter of the system, the material used by the connected pipes, and the ends that are fitted to accommodate the valve. In addition, valves can be operated manually or automatically, and can be activated remotely or on-site. Automatic valves can be activated by an electric, pneumatic, or hydraulic actuator.
Understanding the function of the valve, its situation, and the materials that it is handling will allow you to choose the right type of valve for your application. Once the type of the valve is determined, it is important to know how it will be integrated into the system. Different assembly or installation types will determine if it needs to be welded, bolted through flanges, or screwed in.
The technical characteristics of an installation, in particular temperature, flow, and pressure, will allow you to determine the dimensions of your valve and its material composition. Operating temperatures, as well as the ambient temperature in which the valve body is operating are important considerations for determining the size of the valve. Undersized valves will result in leaks and ruptures, while oversized ones will result in access weight and space requirements. It is important to know the extreme temperatures and pressures that the valve will have to undergo in order to be able to choose a valve designed to tolerate those conditions. This will also influence the types of materials used for the manufacture of the body, the closure system, and the sealing parts.
Working pressure as per material:
Temperature range as per material:
End Connections as per standards
The above permissible temperature values indicate the limits within which each respective material can operate, not the working temperature range for the valve body made from that material. The permissible temperature range for a given valve depends mainly on its configuration and the sealing material.
Types of Valves
Different types of valves are suited for different applications.
- Butterfly valves are mainly used to control the flow rate of fluids. It is a quarter-turn valve and requires a 90° rotation between the open and closed positions. Butterfly valves are designed to ensure a good sealing system. Large-diameter butterfly valves often use flange mounting and screw-in valves. Butterfly valves usually have a minimal space requirement, especially compared to ball valves. The disc, which is located inside the body, pivots a quarter turn (90°) around a stem. Because it has the smallest and most compact face of all valves, the butterfly valve is lightweight and easy to mount and demount.
Type of Butterfly Valve:
- Resilient butterfly valve, which has a flexible rubber seat. Working pressure 232PSI
- High-performance butterfly valve, which uses double eccentric in design. Working pressure up to 725 PSI
- Tricentric butterfly valve, which is usually with a metal seated design. Working pressure up to 1450 PSI
End connections of a butterfly valve:
- Wafer Style Butterfly Valves
- Lug Style Butterfly Valves
- Flanges Style Butterfly Valves
- Gate valves control the flow of liquids by a valve that lifts and lowers a gate. Gate valves are suitable for full-on, full-off flow control. Turning the handle counterclockwise raises the disc, allowing flow through a valve. Turning the handle clockwise lowers the disc, impeding flow. Ball valves are quarter-turn valves that have the advantage of not obstructing the flow of fluids when in the open or full-flow position. They are used for both liquids and gases.
- Check valves allow only one direction for fluid flow. They are known as one-way valves because they only allow media to flow in one direction. A check valve’s primary function is to prevent backflow in the system.
Three types of check valves are available to achieve this checking effect.
- Swing Check Valve: A hinged disc assembly is suspended from the body to allow it to move freely. This configuration minimizes pressure loss and eases fluid flow. Swing check valves can be used for either horizontal or vertical (fluid flowing upward) pipe layouts.
- Lift Check Valve: The lift check valve is a globe valve without a stem, handle, or other opening/closing parts and with an added cover. Because of its large fluid resistance, this valve is used primarily for small-bore applications.
- Wafer Check Valve: Wafer Type Swing Check Valve has short face-to-face dimensions and low weight, allowing a simple space-saving installation between the companion flanges. The valves are suitable for mounting between weld neck or slip-on plate-type companion flanges of different standards. The short face-to-face dimensions and the low weight guarantee a simple and space-saving installation between the bolts of the connecting flange.
- Manifold valves are often used within a larger system to isolate and control flow, such as the movement of liquids between pumps and actuators. These valves are also used to regulate flow in multiple directions.
- Globe valve is named after its shape. Its body has an interior partition, and the valve inlet and outlet centers are inline. This configuration forces a change in the direction of flow in the form of an S. The disc/plug obstructs the flow of fluid by pressing against the seat in the partition. By simply changing the disc shape, globe valves can be used for both throttling (controlling flow rate) and for full-on, full-off flow control. Globe valves can be used for 3 types of flow: Straight, angle, and cross flow. They are generally used for gas and toxic flow line applications.
- Ball Valve: The valve disc is in the shape of a ball, and it is constructed with a soft seat for low-temperature application and a metal seat for high pressure and temperature. Ball valves are suitable for use with full-on, full-off flow control in general service. Due to their material and construction, ball valves are not appropriate for use in applications that require partial opening of the valve. The ball is usually rotated through the use of a lever handle. The ball allows straight-through flow when it remains in the open position, and it prevents flow-through when the handle is rotated a quarter turn (90°). Because larger valves require more force to operate; they are equipped with a gear handle in place of a lever handle.
Choosing the Right Partner
In conducting due diligence when choosing a supplier for your valve requirements, you need to ensure that your supplier is working with manufacturers with a solid reputation and adherence to industry standards and specifications. The American Society of Mechanical Engineers (ASME) provides specifications for mechanical engineering applications and codes that govern the safety of mechanical equipment. The American Petroleum Institute (API), on the other hand, produces recommended guidelines. There are more than 700 API standards in the valve industry. They are designed to improve operational safety, environmental sustainability, and to regulate usage, including in the oil and gas industry.
Valve installation and fastening is an important element in their function and that of the system at large. This needs to be professionally done in order not to compromise the system’s performance. Valves that are not fastened correctly or that occur when a valve is shut too quickly can result in water hammer – excessive pressure that can create significant damage or collapse of a system. When choosing a supplier, ensure that they have experience in handling valve operations in order to prevent consequential damage.
At Gerab National Enterprises, we have been relied on by some of the world’s leading NOCs, IOCs, contractors, and consultants to provide complete pipe system solutions for a wide range of applications in energy, municipal, and industrial projects. This level of trust could not have been achieved without providing comprehensive solutions that include attention the most critical part of a pipe system – the valves that hold it all in place and regulates its conduit’s flow and proper functioning. The key learning from that experience is that you have to have the right materials and the right expertise, and to be able to deliver on time valves from reputable suppliers – with no margin for error.