Control Valves Types,Operation and Troubleshooting

[Music] valves are used to control the flow of fluids and process systems in order to meet the needs of a process system some method of changing the positions of valves is needed some valves can be operated with hand wheels or levers but some valves have to be opened closed or throttled frequently manually positioning valves in these types of situations is not always practical so instead of hand wheels or levers actuators are used to position the valves we'll define an actuator as a mechanism that moves or controls a device such as a valve actuators reduce the need for operators to go to every valve that needs repositioning and operate the valve by hand when actuators are used Valve's can be repositioned from a central remote location such as a control room this is very important in processes where a number of valves have to be repositioned accurately and quickly there are three basic types of actuators pneumatic actuators hydraulic actuators and electric actuators pneumatic actuators use air pressure to produce motion to position a valve they're probably the most common type of actuator used in process systems actuators that are powered by a pressurized liquid such as hydraulic fluid are called hydraulic actuators compared to pneumatic actuators hydraulic actuators of the same size are usually more powerful electric actuators use electricity to produce motion they usually fall into one of two general classifications solenoid actuators or motor driven actuators this type is often referred to as a motor operator regardless of the type of actuator that's used Valve's with actuators are normally part of process control systems from a control room valves with actuators can be quickly and accurately positioned to deal with frequent flow changes valve actuators operate in position valves in response to signals from controllers controllers are part of the instrumentation systems that monitor plant processes and respond to variations in the processes basically a controller is a device that receives an input from another part of the instrumentation system compares that input to a setpoint and sends out a corrective signal to regulate the value of a process variable such as temperature pressure level or flow generally actuators are used with valves that are designed for throttling or regulating flow valves that are used to automatically throttle flow are generally referred to as control valves however some on/off or isolation valves may also require actuators although these isolation valves may require actuators they're not commonly referred to as control valves control valves work in basically the same way as manually operated valves control valves can be either linear that is the stem moves the valve disk up and down as in globe valves or they can be rotary which means that they're positioned by rotation butterfly valves which open or closed with a 90 degree turn our examples of rotary control valves this is a globe type control valve it has the same basic parts as a manually operated valve including a valve body a disc a seat a bonnet a stem and a packing assembly control valves also have parts that may not be on manually operated valves for example control valves like this one generally include guides that align the valve stem and disc with the valve seat these guides help ensure precise control when the valve is opened and closed the upper stem guide on this valve is housed above the packing inside this part of the packing assembly this is the lower guide which is held in place by this part of the valve called a cage part of this cage along with other valve parts have been cut away to better show the valves construction the cage is a hollow cylinder containing openings when the valve disc is moved away from the seat fluid flows up through the seat through the cage openings and out of the valve one of the most common types of pneumatic actuators is the diaphragm actuator in a diaphragm actuator air pressure acts on a flexible diaphragm to position a valve a single acting diaphragm actuator is called single acting because air pressure acts on only one side of the diaphragm to position a valve a typical single acting diaphragm actuator consists of a casing a diaphragm an air supply port an air vent a spring a stem and a valve position indicator the indicator shows the position of the valve the center of the diaphragm is supported by metal plates and the outer edge is sandwiched between the rims of the upper and lower halves of the casing to form an airtight seal this arrangement divides the casing into two chambers an upper chamber and a lower chamber the upper end of the actuators stem is connected to the metal plates in the diaphragm and the lower end moves the valve disk when the actuator receives a signal from a controller to close the valve air pressure is applied to the upper chamber the diaphragm and the actuator stem are pushed downward the spring is compressed and the valve closes air in the lower chamber is exhausted through the air vent when air pressure to the upper chamber is reduced the spring moves the actuator stem upward and the valve opens these actions make stem movement and therefore valve position proportional to the amount of air pressure applied to the actuator controlling the applied pressure enables the actuator to position the valve anywhere within the limits of travel for the actuator this type of actuator can be called an air to close spring to open actuator because air pressure moves the stem to close the valve and a spring moves the stem to open the valve this means that if air pressure to the actuator is lost the control valve connected to the actuator will fail open since spring pressure would raise the stem and open the valve a single acting diaphragm actuator that's designed to close a valve or fail closed when air pressure is lost looks like this as you can see it's very similar to the actuator we just looked at during off a race air pressure is fed into the lower chamber this causes the diaphragm to lift which expands the spring raises the stem and opens the valve when air pressure is reduced the spring pulls the diaphragm and the stem downward closing the valve a control valve using this kind of actuator is said to fail closed because if air pressure is lost the spring in the actuator will close the valve a diaphragm actuator with an airline to only the lower chamber is typically an air to open spring to closed type which causes a control valve to fail closed an actuator with an airline to only the upper chamber is typically an air to close spring to open type which causes a control valve to fail open by controlling the applied pressure either of these actuators can be used to position a valve anywhere within the limits of travel for the actuator regardless of how they operate single acting diaphragm actuators are usually represented on process piping diagrams by this symbol a double-acting diaphragm actuator is called double acting because air pressure acts on both sides of a flexible diaphragm to position a valve a double acting diaphragm actuator consists of a casing a flexible diaphragm an upper air supply port a lower air supply port a stem and a valve position indicator which shows the position of the valve the center of the diaphragm is supported by metal plates and the outer edge is sandwiched between the rims of the upper and lower halves of the casing to form an airtight seal this arrangement divides the casing into two chambers an upper chamber and a lower chamber the upper end of the actuator stem is connected to the metal plates and the diaphragm and the lower end is connected to the valve stem when air pressure is applied to the upper chamber the diaphragm and the actuator stem are pushed downward and the valve closes air in the lower chamber is exhausted through the lower air supply port when air pressure is applied to the lower chamber the diaphragm and the stem are pushed upward and the valve open air in the upper chamber is exhausted through the upper air supply port these actions make stem movement and therefore valve position proportional to the difference between the two air pressures applied to the chambers of the actuator controlling the applied pressures enables the actuator to position the valve anywhere within the limits of travel for the actuator in most applications accurate positioning is achieved by using a device such as a positioner to add air to one side of the diaphragm and bleed it off the other side on a piping system diagram a double-acting diaphragm actuator may be represented by this symbol however it may also be represented by the same symbol used to represent a single acting diaphragm actuator some valves require relatively long stem travel or a large amount of force to be positioned in these situations a piston actuator is probably more suitable than other types of actuators this is one type of piston actuator it's called a single acting piston actuator because a controller or similar device controls the air pressure on one side of a piston when air is fed through this air supply port the piston moves along in a cylinder compressing a spring and opening the valve air on the other side of the piston leaves the cylinder through an air vent when air pressure is reduced the spring expands moving the piston in the opposite direction closing the valve if air pressure drops below a predetermined value or is lost completely the spring will force the piston down to close the valve in other words the valve will fail closed since air pressure is only fed to one side of the piston this type of actuator is called single acting however there are piston actuators that have air pressure supplied to both sides of the piston this type of actuator is called double acting the parts of a double acting piston actuator are similar to those of the single acting actuator however this one doesn't have a spring and there's an air supply port on each end of the cylinder when air pressure is fed into this supply port it pushes against one the piston which moves the piston to open the valve air on the other side of the piston is bled off through the other air supply port when air is fed in through the supply port in the opposite end the piston is pushed in the other direction closing the valve air is bled off through the other supply port filling the cylinder with air and bleeding air from the cylinder can be controlled by a device called a positioner on a piping system diagram single acting and double acting piston actuators may be represented by this symbol however a double acting piston actuator may also be represented by this symbol a vane actuator uses air pressure acting against a paddle or vane to position a valve in general a vane actuator is simple in design and relatively small for the amount of force it can supply to open or close a valve vane actuators are used primarily with rotary type valves such as ball plug and butterfly valves because the vane rotates the valve disk here's a cutaway of a vane actuator that operates a butterfly valve when air pressure is supplied through this air supply port of the vane actuator it pushes against a vein causing the vein to swing across a housing this turns a shaft as the shaft turns it opens the valve air on the other side of the vein is bled off through another air supply port when air pressure is supplied to the opposite supply port the vane is moved in the opposite direction closing the valve air on the other side of the vane leaves through the other supply port vane actuators like other actuators can be spring-loaded or set up with other devices so that a valve will fail in a safe position on a piping system diagram a vane actuator can be represented by this symbol pneumatic actuators are commonly operated by air signals that come from a controller in some cases the controller signal alone isn't enough to overcome forces on the actuator such as friction in the actuator or the valve stem or fluid pressure acting against the valve disc to overcome these forces some actuators must be provided with a different supply of air that's capable of applying higher pressures than the air signals from the controller this is accomplished by using a positioner along with the actuator basically a positioner is a device that uses a separate supply of air to ensure that an actuator correctly positions a valve in response to a change in the air signal from a controller in other words a positioners job is to place the control valve in the position called for by the controller the position are shown here has three gauges one gauge indicates the supply air pressure to the positioner and another indicates the output air pressure to the actuator the third gauge indicates the input signal pressure from the controller a mechanical linkage joins the actuator stem to the positioner this mechanical linkage may also be called a feedback linkage as the actuator stem moves up or down it also moves the linkage the position of the linkage indicates to the positioner when enough movement has occurred to correspond with the air signal from the controller when a positioner is used with an actuator the signal from the controller goes to the positioner instead of directly to the actuator the positioner controls a source of air that enters here and is sent to the actuator through this line when the controller sends a signal to close the valve the positioner receives the signal and converts it to the appropriate air pressure using this air supply this pressure is then applied to the actuator to close the valve the feedback linkage indicates to the positioner how far the valve is from the desired position in this case fully closed as the valve moves toward the fully closed position the feedback linkage causes the positioner to change the air signal to the actuator so that as the valve reaches the fully closed position actuator movement is stopped on a piping system diagram a positioner may be represented by this symbol actuators like other process components are susceptible to mechanical problems since an actuator problem can adversely affect the operation of a process it's important to know how to identify actuator problems when they occur the following discussion is not intended to enable you to isolate the exact cause of an actuator or control valve failure but it can be used to help you narrow down the scope of a problem to minimize the effect it has on a process often an operator can detect an actuator problem by looking at its valve position indicator and comparing it to the position called for by the controller for example if the position indicator is showing that the valve is closed but the flow indicator on the controller is showing that the flow is still continuing through the valve then the valve seat and disc are probably warm allowing leakage through the valve however if the position indicator shows that the valve is open when it should be closed the problem could be in some other part of the control valve or in the actuator for example a diaphragm actuator will not be able to properly position its control valve if its diaphragm ruptures or if air pressure to the actuator is lost loss of air pressure could result from leaks in the actuator around the diaphragm edge from leaks in the air lines to the actuator or from a crimp that blocks the flow of air in an air line going to the actuator if a positioner is used on an actuator its gauges should be checked to make sure they have the appropriate air pressure readings sometimes problems with a positioner can also result from a loose or broken feedback linkage so it should be checked - regardless of the reason for the failure of an actuator or a control valve there are some basic steps that can be taken to minimize the effect that the failure has on the process some actuators have manual operators on them that may be used to regain control of the process flow in the event of an actuator failure while other actuators and control valves may have manual bypass lines around the failed components bypass lines can usually be placed in service by isolating the failed actuators control valve and positioning the bypass valve to restore flow when either a manual operator on an actuator or a bypass line around an actuator is used it will probably be necessary to maintain Commun occations with the control room to ensure that the proper flow rates are maintained in the process since there's so many different possible configurations that actuators and control valves can be arranged in you should check your company's procedures before operating any actuator manually or on the bypass [Music]

Channel: Technical Engineering School

Views: 152,131

Keywords: flow control valve, hydraulic actuator, pressure actuator, pneumatic control valve, actuator driver, actuator cylinder, control4, pneumatic actuation system, iot actuators, the actuator, Troubleshooting, Control Valves, Types, Operation, what's an actuator, actuate, how, actuator, VALVE, control, how flow control valves work, what does flow control valve stand for, picv, control valves, control valve, Control Valves Types, Control Valves Operation, Control Valves Troubleshooting

Id: XDyTPlkwKak

Length: 18min 12sec (1092 seconds)

Published: Mon Feb 18 2019