VALVESA valve is a mechanical device that controls the flow of fluid and pressure within a system or process. A valve controls system orprocess fluid flow and pressure by performing any of the following functions: • Stopping and starting fluid flow • Varying (throttling) the amount of fluid flow • Controlling the direction of fluid flow • Regulating downstream system or process pressure • Relieving component or piping over pressureGate ValveA gate valve is a linear motion valve used to start or stop fluid flow; however, it does not regulate or throttle flow. The name gate isderived from the appearance of the disk in the flow stream. The disk of a gate valve is completely removed from the flow stream when the valve is fully open. This characteristic offers virtually no resistance to flow when the valve is open. Hence, there is little pressure drop across an open gate valve. When the valve is fully closed, a disk-to-seal ring contact surface exists for 360°, and good sealing is provided. With the proper mating of a disk to the seal ring, very little or no leakage occurs across the disk when the gate valve is closed. On opening the gate valve, the flow path is enlarged in a highly nonlinear manner with respect to percent of opening. This means that flow rate does not change evenly with stem travel. Also, a partially open gate disk tends to vibrate from the fluid flow. Most of the flow change occurs near shutoff with a relatively high fluid velocity causing disk and seat wear and eventual leakage if used to regulate flow. For these reasons, gate valves are not used to regulate or throttle flow. A gate valve can be used for a wide variety of fluids and provides a tight seal when closed. The major disadvantages to the use of a gate valve are: • It is not suitable for throttling applications. • It is prone to vibration in the partially open state. • It is more subject to seat and disk wear than a globe valve. • Repairs, such as lapping and grinding, are generally more difficult to accomplish.Ball ValveA ball valve is a rotational motion valve that uses a ball-shaped disk to stop or start fluid flow. The ball, shown in Figure 12, performsthe same function as the disk in the globe valve. When the valve handle is turned to open the valve, the ball rotates to a point wherethe hole through the ball is in line with the valve body inlet and outlet. When the valve is shut, the ball is rotated so that the hole isperpendicular to the flow openings of the valve body and the flow is stopped. Most ball valve actuators are of the quick-acting type, which require a 90° turn of the valve handle to operate the valve. Other ball valve actuators are planetary gear-operated. This type of gearing allows the use of a relatively small handwheel and operating force to operate a fairly large valve. Some ball valves have been developed with a spherical surface coated plug that is off to one side in the open position and rotates into the flow passage until it blocks the flowpath completely. Seating is accomplished by the eccentric movement of the plug. The valve requires no lubrication and can be used for throttling service. Advantages A ball valve is generally the least expensive of any valve configuration and has low maintenance costs. In addition to quick, quarter turn on-off operation, ball valves are compact, require no lubrication, and give tight sealing with low torque. Disadvantages
Conventional ball valves have relatively poor throttling characteristics. In a throttling position, the partially exposed seat rapidly erodes because of the impingement of high velocity flow.Butterfly ValvesA butterfly valve, illustrated in Figure 19, is a rotary motion valve that is used to stop, regulate, and start fluid flow. Butterfly valves are easily and quicklyoperated because a 90o rotation of the handle moves the disk from a fully closed to fully opened position. Larger butterfly valves are actuated byhandwheels connected to the stem through gears that provide mechanical advantage at the expense of speed.Butterfly valves possess many advantages over gate, globe, plug, and ball valves, especially for large valve applications. Savings in weight, space, andcost are the most obvious advantages. The maintenance costs are usually low because there are a minimal number of moving parts and there are nopockets to trap fluids. Butterfly valves are especially well-suited for the handling of large flows of liquids or gases at relatively low pressures and for the handling of slurries or liquids with large amounts of suspended solids. Butterfly valves are built on the principle of a pipe damper. The flow control element is a disk of approximately the same diameter as the inside diameter of the adjoining pipe, which rotates on either a vertical or horizontal axis. When the disk lies parallel to the piping run, the valve is fully opened. When the disk approaches the perpendicular position, the valve is shut. Intermediate positions, for throttling purposes, can be secured in place by handle-locking devices. Needle Valves A needle valve, as shown in Figure 20, is used to make relatively fine adjustments in the amount of fluid flow. The distinguishing characteristic of a needle valve is the long, tapered, needlelike point on the end of the valve stem. This "needle" acts as a disk. The longer part of the needle is smaller than the orifice in the valve seat and passes through the orifice before the needle seats. This arrangement permits a very gradual increase or decrease in the size of the opening. Needle valves are often used as component parts of other, more complicated valves. For example, they are used in some types of reducing valves. Needle Valve Applications Most constant pressure pump governors have needle valves to minimize the effects of fluctuations in pump discharge pressure. Needle valves are also used in some components of automatic combustion control systems where very precise flow regulation is necessary Check Valve Check valves are designed to prevent the reversal of flow in a piping system. These valves are activated by the flowing material in the pipeline. The pressure of the fluid passing through the system opens the valve, while any reversal of flow will close the valve. Closure is accomplished by the weight of the check mechanism, by back pressure, by a spring, or by a combination of these means.Relief and Safety ValvesRelief and safety valves prevent equipment damage by relieving accidental over-pressurization of fluid systems. The main difference between a reliefvalve and a safety valve is the extent of opening at the setpoint pressure.A relief valve, illustrated in Figure 28, gradually opens as the inlet pressure increases above the setpoint. A relief valve opens only as necessary torelieve the over-pressure condition. A safety valve, illustrated in Figure 29, rapidly pops fully open as soon as the pressure setting is reached.A safety valve will stay fully open until the pressure drops below a reset pressure. The reset pressure is lower than the actuating pressure setpoint. Thedifference between the actuating pressure setpoint and the pressure at which the safety valve resets is called blowdown. Blowdown is expressed as apercentage of the actuating pressure setpoint.
Relief valves are typically used for incompressible fluids such as water or oil. Safety valves are typically used for compressible fluids such as steam orother gases. Safety valves can often be distinguished by the presence of an external lever at the top of the valve body, which is used as an operationalcheck.As indicated in Figure 29, system pressure provides a force that is attempting to push the disk of the safety valve off its seat. Spring pressure on thestem is forcing the disk onto the seat. At the pressure determined by spring compression, system pressure overcomes spring pressure and the reliefvalve opens. As system pressure is relieved, the valve closes when spring pressure again overcomes system pressure. Most relief and safety valvesopen against the force of a compression spring. The pressure setpoint is adjusted by turning the adjusting nuts on top of the yoke to increase ordecrease the spring compression.Nipple: A Pipe Nipple is a short pipe (12 inches or less), with small opening which provides way for the liquids or gases to pass through the pipe. Ithas a male thread on each end and is used for extension from a fitting. Some of the popular usages of Pipe Nipple are : • Used in fluid application to connect two FPT fittings. • Used in plumbing system or for ceiling and wall supports and extensions. • Used for ceiling or wall supports. • Used to extend shower riser. We saw different types of nipples in our fluid mechanics lab. These are: 1. Barrel nipple 2. Hexagonal nipple (1) Barrel Nipple: Applications: Male Pipe to Male Pipe connections
Figure: Barrel Nipple Figure: Hexagonal Nipple (2) Hexagonal Nipple: Applications: Male Pipe to Male Pipe connectionsElbow: A pipe fitting installed between two lengths of pipe or tube allowing a change of direction, usually 90° or 45°. The ends may be machined forbutt welding, threaded (usually female), or socketed, etc. When the two ends differ in size, it is called a reducing or reducer elbow. Most elbows areavailable in short radius or long radius of types. We saw different types of elbows in our fluid mechanics lab. These are: 1. 90 degree elbow 2. 45 degree elbow 3. Male female elbow 4. Equal elbow (1) 90 degree elbow: 90 degree elbow, also called "90 bends or 90 ells", are manufactured as SR (Short Radius) elbows and LR (Long Radius) elbows. Applications: The main application area of an elbow (90 degree) is to connect hoses to valves, water pressure pumps, and deck drains. These elbows can be made from tough nylon material or NPT thread. Figure: 90 degree elbow (2) 45 degree elbow: 45 degree elbow, also called "45 bends or 45 ells" are typically made as LR (Long Radius) elbows. Available in various sizes (in mm or inches), 45 degree pipe elbow is available with different male to female BSP thread connections. Applications:
• Water supply facilities • Food industrial pipeline networks • Chemical industrial pipeline networks • Electronic industrial pipeline networks • Air conditioning facility pipeline • Agriculture and garden production transporting system Figure: 45 degree elbow(3) Male female elbow and connectors: Application of Male Female Connector and elbow Male Female connectors and elbow are put to use in a number of industries depending on their specifications and internal and external diameter. • Pharmaceutical fittings • Pneumatic tube fittings • Air brake fittings • Gas fittings • Refrigerant fittings Figure: male female elbow(4) Equal elbow: Equal elbows are quick-connect fittings that are extremely helpful in routing water lines that are laid in confined areas. They are known as elbow fittings because they display an angular bent so that two pipes can be easily fixed in the same manner. Applications:
1. Mains fed and indirect cold water systems. 2. Vented and unvented hot water systems. 3. Vented and sealed central heating systems. Figure: Equal elbowUnion Cross Union cross is essentially used for piping of tube to tube industrial fittings and connect fractional tubes.These metal fittings offer high mechanical connections for vacuum applications and positive pressure in tube totube piping systems. Union cross are so designed, that they can be used with orbital weld equipment, theseunique fittings have enhanced surface to prevent out gassing and prevent corrosion. These widely used tubefittings allow smooth flow paths and prevent any kind of turbulence or entrapments. These tubing connectionseliminate costly, hazardous leaks in instrumentation and process tubing and are available in metric and inchesspecifications according to various applications.Union and Socket: A union is similar to a coupling, except it is designed to allow quick and convenient disconnection ofpipes for maintenance or fixture replacement. While a coupling would require either solvent welding or being ableto rotate all the pipes adjacent as with a threaded coupling, a union provides a simple nut transition, allowingeasy release at any time. We saw different types of unions in our fluid mechanics lab. These are: 1. Male female union 2. Union jointAn opening in any fitting that matches the outside diameter of a pipe or tube, with a further recessed through opening matching the inside diameter ofthe same pipe or tube. We saw different types of unions in our fluid mechanics lab. These are: 1. Half socket 2. Co-centric reducing socket Application of male female union, union joint, half socket are quite equivalent. These are: • Pharmaceutical fittings • Pneumatic tube fittings • Air brake fittings • Gas fittings • Refrigerant fittings
as Male union Female Concentric Reducing Socket Half union SocReducer: A reducer normally refers to a fitting that is used to reduce the diameter of the suction piping to fit the pump intake. It is thus used tojoin two pipes of different sizes. Reducer is available in both eccentric and concentric designs. Concentric or eccentric reducers are used to properlyreduce into and out of circulating pumps. The various advantages include keeping big pipes and small pipes together as well as reducing noise andvibration at the same time. Applications: Some of the industries where they find application are oil, gas, petrochemical, onshore and offshore sectors. They are used in both cargotransfers operations and vapor recovery systems. Reducers for vapor recovery include a pin on one flange and vapor hole on the opposite flange.Concentric reducer save installation space and reduce costs. Piping systems must be anchored when using concentric reducer. Figure: reducerImpeller: An impeller is a rotor inside a tube or conduit to increase the pressure and flow of a fluid. We saw different types of unions in our fluid mechanics lab. These are:
4. Semi-open impeller 5. Closed impeller 6. Open impeller Figure: ImpellerReducing coupler: Application: Used for reducing area, pressure, flow and used for connections. Figure: Reducing CouplerHexagonal nut: Application: Used for joining pipes. Figure: Hexagonal NutEqual Tee: A tee is amongst the most common pipe fittings and is available with all female thread sockets, all solvent weld sockets, or withopposed solvent weld sockets and a side outlet with female threads. This is a T-shaped device which has three openings that act as an outlet for thepipe. Applications: A tee is used for connecting pipes of different diameters or for changing the direction of pipe runs.
Figure: TeeLong and Short bend: Applications: Use for small and large pipe connections between pipes. Figure: Short Bend Figure: Long bendCentrifugal Pump: A centrifugal pump is a rotodynamic pump that uses a rotating impeller to increase the pressure of a fluid. Centrifugal pumps arecommonly used to move liquids through a piping system. The fluid enters the pump impeller along or near to the rotating axis and is accelerated by theimpeller, flowing radially outward into a diffuser or volute chamber (casing), from where it exits into the downstream piping system. Centrifugal pumpsare used for large discharge through smaller heads.
Figure: Centrifugal PumpGASKET A gasket is a mechanical seal that fills the space between two objects, generally to preventleakage between the two objects while under compression. Gaskets save money by allowing "less-than-perfect" mating surfaces on machine parts which can use a gasket to fill irregularities. Gasketsare commonly produced by cutting from sheet materials, such as gasket paper, rubber, silicon, metal,cork, fiberglass or a plastic polymer. Gaskets for specific aplications may contain asbestos. It is usually desirable that the gasket be made from a material that is to some degreeyielding such that it is able to deform and tightly fills the space it is designed for, including any slightirregularities. Many gaskets require an application of sealant directly to the gasket surface to functionproperly.