VALVE TERMINOLOGY

Valve Flow Coefficient (Cv) - The number of US gallons per minute of 60°F water that will flow through a valve with a one pound per square inch pressure drop

Rated Cv - The value of Cv at the valve full-open position

Rated Travel - The linear movement of the valve plug from the closed position to the valve full - open position

Leakage - The quantity of fluid passing through an assembled valve when the valve is in the closed position

On-Off Service - When the valve is used to start / stop the flow by being cycled to the full open or to full closed position

Modulating Service - When the valve is being used to throttle or regulate the flow by varying the opening between open and closed positions

Maximum shut-off Pressure - The pressure of the fluid flowing into the valve against which the valve will have to close

Service Temperature - The maximum and minimum temperature of the media

Supply Pressure - The plant air supply pressure available to operate a pneumatic actuator

Stem Torque - The force required at the valve stem to open or close the valve against system pressure and service conditions

Capactiy - Rate of flow through the valve under stated conditions

Fail - close - The condition wherein the valve port remains closed should the actuating power fail

Fail - open - The condition wherein the valve port remains open should the actuating power fail

Fail - last - The condition wherein the valve port remains in the last position should the actuating power fail

Valve body

Valve body - A housing for internal parts having inlet and outlet flow connections

Bonnet - The part of the body assembly which serves as a means for mounting the actuator

Cage - A hollow cylindrical trim element that is a guide to align the movement of a valve plug with a seat ring.

Seat - The portion of the valve body where the valve plug contacts for closure.

Valve Plug - A movable part which provides a variable restriction in a port.

Valve Plug Stem - A rod extending through the bonnet assembly to position the valve plug.

Trim - The internal parts of the valve which are in contact with the controlled fluid

Port - A fixed opening inside the diameter of the seat ring through which the fluid passes

Packing Box - The part of the bonnet assembly used to seal against leakage around the valve plug stem

Actuator

Actuator - An air operated mechanical device used to open and close or modulate a valve. The actuator is designed to convert air pressure into mechanical force sufficient to operate the valve.

Diaphragm - A flexible pressure responsive element which transmits the force to the actuator stem

Actuator stem - The extension of the diaphragm plate or piston for connection to the valve plug stem

Actuator spring - The spring enclosed in the yoke is to move the actuator stem in a direction opposite to that created by the diaphragm pressure

Piston - A movable pressure responsive element which transmits force to the operating fluid

Yoke - The structure by which the diaphragm case is supported rigidly on the bonnet.

Travel Indicator - A pointer to indicate the travel of the valve plug.

Travel indicator scale - A graduated scale attached to the yoke for indication of the travel.

Gate valves

Gate valves (also known as knife valves or slide valves) are linear motion valves in which a flat closure element slides into the flow stream to provide shut-off. Gate valves and knife valves are designed to minimize pressure drop across the valve in the fully opened position and stop the flow of fluid completely. The direction of fluid flow does not change, and the diameter through which the process fluid passes is essentially equal to that of the pipe. Hence, they tend to have minimal pressure drop when opened fully.

Gate valves and knife valves are advantageous in applications involving slurries, as their “gates” can cut right through the slurry. They are also used in applications that involve viscous liquids such as heavy oils, light grease, varnish, molasses, honey, cream and other non-flammable viscous liquids. They are available in large sizes to better handle thick flow. However, gate valves do have low-pressure limitations, and are not optimal in applications that require cleanliness or sanitary conditions. They are excellent for use anywhere a shutoff valve is needed. They can also be used where throttling capabilities are desired, although this is not generally recommended as erosion of the seat and disc occurs due to the vibrations of the disk in throttling applications.

Gate valves are usually divided into two types: parallel and wedge-shaped. The parallel gate valve uses a flat disc gate between two parallel seats, upstream and downstream. Knife valves are of this type, but with a sharp edge on the bottom of the gate to shear entrained solids or separate slurries.

• Controlling device - Knife vane
• Minimum resistance to flow
• Easy maintenance
• Quick and easy to operate
• Utilites (water & waster-water)
• Slurry applications
• Multiproduct lines

Globe valves

Globe valves are linear motion valves with rounded bodies, from which their name is derived. They are widely used in industry to regulate fluid flow in both on/off and throttling service. Globe valves consist of the following moving parts – the disk, the valve stem, and the handwheel. The stem connects the handwheel and the disk. It is threaded and fits into the threads in the valve bonnet. The location of the valve disk in relation to the valve seat allows or restricts flow. The direction of fluid flow through the valve changes several times, which increases the pressure drop across the valve. In most cases, globe valves are installed with the stem vertical and the higher-pressure fluid stream connected to the pipe side above the disk, which helps to maintain a tight seal when the valve is fully closed.

When globe valves are open, the fluid flows through the space between the edge of the disk and the seat. These valves are commonly used as a fully open or fully closed on/off valves, but they may be used for throttling as long as fine adjustments are not required.

These linear motion valves can be used in a variety of applications as long as the pressure and temperature limits are not exceeded, and the process does not require special materials to combat corrosion. Globe valves are generally available in a variety of metal and alloy constructions, as well as plastics, to cover this wide range of industrial applications. Proper material compatibility requires knowledge of the type, concentration and temperature of the media being handled. It may be necessary to consult the manufacturer of the valve for specific properties of the materials used in the valve.

Globe valves provide the following advantages: they offer precise throttling and control and have high-pressure limits. Conversely, they offer a low coefficient of flow and are not good selections in applications that require cleanliness or sterility.

Globe valves are available in three main body types (although custom designs are available as well): angle design, Y-design and multi-piece design. Angle valves are designed so that the inlet and outlet are perpendicular, for transferring flow from vertical to horizontal. Y-design valves derive linear action from the incline between the axis of the inlet and outlet ports. The bodies of multi-piece design valves are bolted together. The inlet and outlet are not of single piece construction

• Controlling device - plug
• High accuracy control with wide range of controllability
• Petrochemical & chemical
• applications Refineries & Gas plants
• Power plants
• Fisher, Masoneillan, CCI

Butterfly valves

Butterfly valves control flow through a circular disc or vane by turning the valve's pivot axis at right angles to the direction of flow in the pipe. They are normally used as throttling valves to control flow.

Butterfly valves are quick opening valves that consist of a metal circular disc or vane with its pivot axes at right angles to the direction of flow in the pipe, which when rotated on a shaft, seals against seats in the valve body. They are normally used as throttling valves to control flow. Butterfly valves control the flow of gas or liquid by means of a disk, which turns on a diametrical axis inside a pipe or by two semicircular plates hinged on a common spindle, which permits flow in only one direction. These valves offer a rotary stem movement of 90 degrees or less, in a compact design. Unlike ball valves, butterfly valves do not have any pockets in which fluids may become trapped when the valve is closed. Butterfly valves are available in several body styles and seal types. The flange type or lug style can be held between flanges of any type. Wafer valves are installed between two flanges using bolts or nuts and studs, while lug style valves have metal inserts installed in the valve's bolt holes and the valve is installed between two flanges using a separate set of bolts for each flange. If the wafer style is used, avoid placing it between either slip-on or screwed flange types. Some wafer body styles will not form a proper seal. The wafer style is used more commonly and is cheaper than the lug style. Butterfly valves offer a number of advantages when used for the proper application. They may be used in a wide variety of chemical services, they are available with small dimensions allowing for use in areas where space is limited, and they allow a high coefficient of flow. Conversely, the design of butterfly valve creates the disadvantage of not being easy to clean, and therefore should be avoided in situations that call for sterile, medical or food processing applications. Additionally, some styles may have difficulty dispensing slurries.

Butterfly valves control flow through a circular disc or vane by turning the valve's pivot axis at right angles to the direction of flow in the pipe. Butterfly valves are quick opening valves that consist of a metal circular disc or vane with its pivot axes at right angles to the direction of flow in the pipe, which when rotated on a shaft, seals against seats in the valve body. They are normally used as throttling valves to control flow. Butterfly valves control the flow of gas or liquid by means of a disk, which turns on a diametrical axis inside a pipe or by two semicircular plates hinged on a common spindle, which permits flow in only one direction. These valves offer a rotary stem movement of 90 degrees or less, in a compact design. Unlike ball valves, actuated butterfly valves do not have any pockets in which fluids may become trapped when the valve is closed. Butterfly valves offer a number of advantages when used for the proper application. They may be used in a wide variety of chemical services, they are available with small dimensions allowing for use in areas where space is limited, and they allow a high coefficient of flow. Conversely, the design of butterfly valve creates the disadvantage of not being easy to clean, and therefore should be avoided in situations that call for sterile, medical or food processing applications. Additionally, some styles may have difficulty dispensing slurries. Specific application butterfly valves include air butterfly valves, sanitary butterfly valves, center line butterfly valves, butterfly control valves, and electric butterfly valves. Butterfly valves manufacturers use many material constructions, which can be implemented depending upon the application and the flow media. These types include stainless steel butterfly valves, PVC butterfly valves, plastic butterfly valves and ceramic butterfly valves.

Controlling device - vane

• Low cost & light weight
• Throttling & isolation applications
• Utilities (Water Supply)
• Chemical Processing
• Power Generation
• Manufacture Keystone, Tomoe, Cooper