1 and Butterfly Valves

PIPING INSTRUMENTS-II Introduction Valves are used to isolate equipment and piping devices, regulate flow, prevent backflow, regulate and relieve pressure. They are critical components of piping systems so that they must be properly located, oriented and configured. Valves operated frequently need careful consideration. There are several kinds of valves: isolation, regulating and safety valves. Isolation valves are used to turn on or turn off fluid flow. Examples are gate, ball, and plug valves; the gate valve is probably the most popular. Knife valves are similar to gate valves but occupy smaller space, weigh less and cost less. Regulating valves are used to control flow direction, rate and pressure. Flow rate valves include globe, butterfly, needle and diaphram. The globe valve is very popular and may be found in lines up to 12” diameter. It has a relatively high pressure drop. The butterfly valve is good for low-pressure lines and offer minimum pressure drop. The needle valve has a needle-like stem with fine threads that allows it to be used for accurate throttling. The diaphram valve is common in the food and beverage industries. Pressure control valves are more often called pressure regulators. Check valves e.g. lift or swing valves prevent back flows and thus protect upstream equipment and personnel. Safety valves are used to limit operating pressures and temperatures. They open at set pressure or temperature values and prevent damage to equipment and personnel. Examples are pop and relief valves. Pop valves are used for air, gas, and steam lines and open at set values. Relief valves are used for liquids and open and close more slowly. A trap is an automatic valve that collects air, water, and gasses in steam lines and discharges them without releasing steam. Flush valves are often of the globe type, and are located at low points of tanks for discharging fluids, slurries, etc. Perhaps valves are the most common type of instruments in piping systems. Isolation Valves Isolation valves are primarily used as of/on control devices, operating at either fully open or fully closed positions. They include gate, ball, and plug valves. These valves are not recommended for use as regulating or throttling devices. Figs 1 and 2 and Plates 1 and 2 show common isolation valves. Quarter-turn valves include plug, ball, and butterfly valves. Plate 1: Stainless steel gate valve Fig. 1: Gate valve Plate 2: Types of ball valves 1 Fig. 2: Ball valve Fig. 3: Plug valve Regulating Valves Regulating valves are used primarily to control flow direction, flow rate, and pressure. Regulating valves consists of throttling and pressure valves. Common throttling valves include globe, butterfly, and diaphragm valves. Figs. 4 to 6 show some common regulating valves while Plate 3 shows a butterfly valve. Fig. 4: Globe valve Fig. 5: Diaphram valve Fig. 6: Butterfly valve Plate 3: Cast iron butterfly valve 2 Protective Valves Protective valves are designed to protect personnel and equipment. They protect personnel from injury or death due to failure of over pressure as well as prevent damage to equipment. Protective valves are used to limit operating pressures and temperatures, and to prevent back flow. They can open at set pressure or temperature values and prevent harm to equipment and personnel. Protective valves include check and safety or relief valves (liquid and gas). Fig. 7 show common types of check valves. a) Swing check valve b) Lift check valve c) Ball check valve d) Stop check valve Fig. 7: Check valves Liquid Relief Valves Relief valves are used for liquid service and open and close relatively slowly. Fig. 8 shows a relief valve. They help maintain pressurized liquids at desired pressure levels by opening automatically to discharge excess pressure. Relief valves operate at relatively low speed, which is fine for liquid systems but is not suitable for gas service. The high speed of flow associated with gasses can damage the disk seat of the valve. Gas Relief (Pop-up) Valves Gas relief valves are commonly called pop-up valves. Fig. 9 shows a pop-up valve. Pop-up valves are employed for gas and vapor services and are used to release excess fluid pressure automatically. They have larger exhaust port compared to relief valves and are fast acting, hence the name “pop-up”. Pop valves are used for air, gas, and steam lines and open at preset pressure values. 3 Fig. 8: Relief valve Fig. 9: Pop-up valve Drain Valves Drain valves are used to remove suspended particles, impurities, and wastes from piping systems. These can clop up the lines and lead to hazards for personnel and equipments. Drain valves include trap, flush, and strainers. Trap is an automatic valve that collects air, water, and gasses in steam lines and discharges them without releasing the steam. Flush valves are often of the globe type, and are located at low points of tanks and lines for discharging fluids, slurries, etc. Strainers are devices that remove impurities and suspended particles from fluids in process lines. Valve Symbols Symbols for valves and other instruments have been standardized internationally (DIN 30600 and ISO 14617) and nationally (ANSI). Fig. 15: Valve symbols Valve Specification 1. Nominal size 4. Body material 2. Pressure class 5. End connection 3. Temperature range 6. Max. fluid viscosity 4 Summary Valves are used to isolate equipment and piping devices, regulate flow, prevent backflow, regulate and relieve pressure. They are critical components of piping systems so that they must be properly located, oriented and configured. The flow control element and seat in a valve is called trim. Quarter-turn valves include plug, ball, and butterfly valves. Globe valves can have a flow control element of several designs such as plug, needle, ball, and composition. Depending on the design of a globe valve, flow can be directed under, above or against the side of the flow control element. An angle valve is a special type of a globe valve. Pressure drop across a globe valve is higher than that over a gate valve. The main parts of a gate valve are the body, stem, trim, and packing. The stem is the long slender rod in a gate valve. The bonnet provides housing for the gate or disk in a gate valve. The flow control element in a gate valve comes in three basic designs of solid split, solid wedge, and parallel disk. The packing gland in a gate valve prevents fluid leakage. They are housed in the stuffing box. Rotating the hand wheel of gate valve closes or opens it. Butterfly valve can be used for throttling service, on-off service and cooling tower water service. A check valve responds to fluid flow and gravity. Diaphram valves are used primarily for corrosive, viscous, and throttling services. Diaphram valves come in weir and non-weir design. A check valve is an automatic valve used to control flow direction. A relief valve is used for liquid service. The common types of valve actuators are pneumatic, electric and hydraulic. Pneumatic actuators are of three basic designs; namely diaphram, piston, and vane. Industrial air is used to operate mainly pneumatic actuators, controllers, and transducers. 5 SUMMARY The flow control element and seat in a valve is called trim. Quarter-turn valves include plug, ball, and butterfly valves. Globe valves can have a flow control element of several designs such as plug, needle, ball, and composition. Depending on the design of a globe valve, flow can be directed under, above or against the side of the flow control element. An angle valve is a special type of a globe valve. Pressure drop across a globe valve is higher than that over a gate valve. The main parts of a gate valve are the body, stem, trim, and packing. The stem is the long slender rod in a gate valve. The bonnet provides housing for the gate or disk in a gate valve. The flow control element in a gate valve comes in three basic designs of solid split, solid wedge, and parallel disk. The packing gland in a gate valve prevents fluid leakage. They are housed in the stuffing box. Rotating the hand wheel of gate valve closes it. Butterfly valve can be used for throttling service, on-off service and cooling tower water service. A check valve responds to fluid flow and gravity. Diaphram valves are used primarily for corrosive, viscous, and throttling services. Diaphram valves come in weir and non-weir design. The common types of actuators are pneumatic, electric and hydraulic. Pneumatic actuators are of three basic designs; namely diaphram, piston, and vane. A check valve is an automatic valve used to control flow direction. A relief valve is used for liquid service. Industrial air is used to operate mainly pneumatic actuators, controllers, and transducers. 6.

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