Showing posts with the label Control Valves

What is a proportional valve?

What is a proportional valve? Basically defines a valve with a spool in a proportional body design. And it is a continuously variable, electrically modulated, directional control valve with more than 3% center overlap. The function of a proportional valve is to produce a smooth and continuous variation in flow or pressure proportional to the electrical input signal. Connecting the electronics to these valves must be done accurately. These valves allow infinite spool positions and result in infinitely adjustable flow volumes. Infinite spool positioning can be achieved using stroke-controlled actuators that use pneumatic cylinders with proportional valves and solenoids to control the direction and speed of motion. In the hydraulic industry, the term proportional valve refers to a specific type of valve that is very specific to a servo valve. Variable positioning of the valve allows spool design with metering notches for flow control, speed control as well as directional control in one va

What is a Servo Valve?

What is a Servo Valve? A servo valve essentially defines a valve design with a bushing spool assembly that has high-precision metering edges. And basically, the name servo valve is related to the word servomechanism, which means that the valve is constantly monitored to control its movement. The name proportional describes any action where only one parameter varies somewhat in relation to the other. It is a continuously variable, electrically modulated, directional control valve with less than 3% center overlap. Servo valves are used in conjunction with closed-loop systems and advanced electronics. Servo valves operate with greater accuracy, very high repeatability, minimal hysteresis and high-frequency response. But servo valves are more expensive. A servo valve or pressure control valve is generally used to control the pressure in a circuit through a directional valve in some cases. A load cell or pressure transducer detects the force or torque. A servo amplifier analyzes the feedbac

What is a pilot or air operated valve?

What is a pilot or air operated valve?  A pilot valve is basically the same as a solenoid valve, however, instead of an electric signal, an air pressure signal will be used to open or close the spool.

What is Quick Exhaust Valve (QEV)?

What is Quick Exhaust Valve (QEV)?  Essentially, the quick exhaust valve is a three-way valve that operates primarily on the differential pressure between the inlet and outlet ports. And this valve finds application where a fast stroke time is required or where air needs to be exhausted quickly from the cylinder. Quick exhaust valves are widely used in actuators and pneumatic cylinders for quick exhaust and stroking applications.

Difference between solenoid valve and motorized valve

Difference between solenoid valve and motorized valve Solenoid valve Solenoid valve works on electromagnetism. Motorized valve A motorized valve operates on an electric motor. Solenoid valve A solenoid valve is a digital output. Motorized valve A motorized valve can have a digital or analog output. Solenoid valve The solenoid valve magnetizes and operates quickly in response to the current, the response is very fast. But, this rapid control does not provide easy passage of fluid. On the contrary. Motorized valve A motorized valve moves very slowly in response to current. Response is slow, but fluid control is accurate and precise. Solenoid valve Solenoid valves are not suitable for high-pressure media. Since the valve opens and closes quickly (usually within a second), the resulting high pressure can damage the valve or damage the pipeline after prolonged use. Motorized valve A motorized valve on the other hand is suitable for any pressure media as it will accurately pass or block the

What is a motorized valve?

What is a motorized valve? Basically motorized valves work on the principle of motor movement. And an electric motor is mounted on the valve and geared to the valve stem so that the valve is open or closed when the motor is running. As the motor is used, it is very much driven by the power supply. And the motor operation is very slow and controlled. When you turn on the motor valve via an external voltage supply, it opens the throttle in a ramp-up slow way. And you close the motor valve, it closes the throttle in a ramp-down slow way.

What is a solenoid valve?

What is a solenoid valve? Solenoid valve basically works on the principle of electromagnetism. It consists of a wire coil which acts like an electromagnet. This coil controls the movement of the mechanical plunger, which ultimately controls the flow of fluid through it. Normally when current is passed through a magnetic coil, a strong electromagnetic field is created. The principle used in this valve When the coil is energized by an external supply voltage, as it is magnetized, an electromagnetic field is created. This field attracts or repels the movement of the plunger, as it is very strong. When energized, the plunger opens the fluid barrier and allows the fluid to escape. When the coil is de-energized, the plunger again closes the opening as the thrust is removed and blocks the passage of fluid. Thus, it can be referred to as digital output

What are the functions of valves in a piping system?

What are the functions of valves in a piping system?  Essentially, valves play a vital role in increasing efficiency, improving quality control and ensuring process safety and reliability. A primary consideration in valve selection is the desired function of the valve. Valves are included in piping systems for one or more of the following reasons Starting or stopping fluid flow.  Throttling flow rates in piping systems.  Pressure regulation.  Regulation of fluid temperature in piping systems.  Redirecting flow from one path to another. Restricting flow to balance the system or prevent overpressure.  Prevent reverse flow of fluid.  Stopping the flow if the system fails.  Improving safety by reducing pressure or vacuum in a piping system. Basically, a valve is a mechanical device used in fluid systems to direct, separate, mix, or control fluid flow or pressure by improving passage through pipes. Normally when the valve is in the open position, the passage flows at a lower pressure than w

Control Valve Interview Questions and Answers

Control Valve Interview Questions and Answers Q. What is a control valve? The control valve is the final component that directly changes the value of the manipulated variable by changing the rate of flow of the control agent. A control valve is a consists of an the operator and the valve body. The operator provides the power to change the position of the valve plug inside the body. The plug is connected to the operator by a stem, which slides through the stuffing box. An air signal from the controller is applied above the diaphragm. An increasing air signal from the controller is applied above the diaphragm. The rising air signal will push down the operator's stem against the force exerted by the spring on the diaphragm plate. The valve is adjusted so that the plug starts moving when 3 psi is applied to the diaphragm and touches the seat when 15 psi is applied to the diaphragm. As the air pressure increases, the valve will close. So the house "want to close". Another

Control valve

Control valve  Control valve is a power operated device to control fluid flow. Control valve is capable of modulating flow at varying degrees between minimum flow and full capacity in response to a signal from the controlling system. Control valve mainly classified by their functions as "on-off" type or "flow regulating" type. Control valve is comprised of an actuator mechanism that is capable of changing the position of flow controlling element in the valve. The control valve modulates or controls flow through movement of a valve plug in relation to the port's located in valve body. The control valve plug is attached to a stem of valve. The actuator, which can be pneumatically operated or electrically operated. The actuator response or responds to an external signal which usually comes from a controller.  Basic valve types  Ball valves  Butterfly valves Globe valves Gate valves

Non return valve

Non return valve A non-return valve allows a medium to flow in only one direction and is fitted to ensure that the medium flows through a pipe in the right direction, where pressure conditions may otherwise cause reversed flow. There are different types of non-return valves, such as spring-loaded, swing type, and clapper type valves. Non-return valves are for example used with mixing loops in heating and cooling systems to ensure proper operation, and with domestic water systems to prevent backflow.  Non return valves basically allow the flow to move in just one direction. As a result, they’re also known as one-way valves. NRVs are also considered a kind of two-port valve as they have two openings: One opening is for exiting and the other is for entering fluids. NRVs usually don’t require manual assistance and function automatically. So most NRVs don’t have stems or handles. Types of Non-Return Valve Lift Check Valve Swing Check Valve Folding Disc Check Valves Tilting Disc Check Valve

Diverter valve

Diverter valve Diverting valves are quite expensive and some types of 3-port valves can suffer from hammering in a diverting application. control strategy for heat exchanger using diverter valve If the process medium temperature is high, the TIC with respect to the measurement TIT opens the three way control valve, so that the flow rate of process medium through cooler is increased and flow rate of process medium through by-pass is decreased. So the temperature of process fluid is decreased, because more fluid is flowed through the cooler. 

Electric actuators

  Electric actuators Electric actuators are motor driven devices that utilize an electrical input signal to generate a motor shaft rotation. This rotation is, in turn, translated by the unit’s linkage into a linear motion,which drives the valve stem and plug assembly for flow modulation. In case of electric signal failure, these actuators can be specified to fail in the stem-out, stem-in, or last position. Commonly used motors for electric actuators include steppers and servos.  steppers A step motor uses gears with increments in the range of 5,000 to 10,000 at 90 degree rotation for accurate positioning at lower speeds. The disadvantage is that steppers may lose synchronization with the controller when employed in an open loop without an encoder or if they are undersized for an application.  servos Servos, by definition, are closed loop and provide superior performance at high speeds, but at a higher cost. High precision screws and anti-backlash mechanics provide accuracies to ten-tho

Pneumatic actuators

  Pneumatic actuators Pneumatic actuators utilize an air signal from an external control device to create a control action via a solenoid. These are commonly available in two main forms Piston actuators Diaphragm actuators Piston actuators Piston actuators are generally used where the stroke of a diaphragm actuator would be too short or the thrust is too small. The compressed air is applied to a solid piston contained within a solid cylinder. Piston actuators can be single acting or double acting, can withstand higher input pressures, and can offer smaller cylinder volumes which can act at high speed. Diaphragm actuators Diaphragm actuators have compressed air applied to a flexible membrane called the diaphragm. These types of actuators are single acting, in that air is only supplied to one side of the diaphragm, and they can be either direct acting (spring-to-retract) or reverse acting (spring-to-extend).  Advantages of Pneumatic Actuators The biggest advantage of the pneumatic actuat


  Actuators   A valve actuator is a device that produces force to open or close the valve utilizing a power source. This source of power can be manual (hand, gear, chain-wheel, lever, etc.) or can be electric, hydraulic or pneumatic. Basic actuators turn valves to either fully opened or fully closed positions. But modern actuators have much more advanced capabilities. They not only act as devices for opening  and closing valves, but also provide intermediate position with high degree of accuracy. The valve actuator can be packaged together with logic control and digital communication ability to allow remote operation as well as allowing predictive maintenance data. Type of Actuators   Pneumatic actuator Electric actuator Pneumatic actuator Pneumatic actuators utilize an air signal from an external control device to create a control action via a solenoid. These are commonly available in two main forms Piston actuators Diaphragm actuators. Electric actuator Electric actuators are motor d

Gate Valves

  Gate Valves Gate valves use linear type of stem motion for opening and closing of a valve. These valves use parallel or wedge shaped discs as closure members that provide tight sealing. Gate valves are a common valve type used for basic on/off service. Manual Gate Valves are operated with a simple hand wheel that causes the stem and gate to rise. When closed, the gate seats against a seat ring, both of which have a special treatment to provide reliable shut-off. Advantages High capacity  Tight shutoff  Low cost  Little resistance to flow  Ability to cut through slurries, scale and surface build-ups Provide unobstructed flow paths that not only provide high flow capacity (Cv), but  even allows slurry, large objects, rocks and items routinely found in mining processes to safely pass through the valve.  Disadvantages Poor control  Cavitate at low pressure drops  Cannot be used for throttling Relatively low pressure limitation - general pressure limitations are 150 psi at maximum.  Uses

Globe Valves

 Globe Valves Globe valves consist of a movable disk-type element and a stationary ring seat in a generally spherical body. The valve stem moves a globe plug relative to the valve seat. The globe plug can be at any position between fully opened and fully closed to control flow through the valve. The globe and seat construction gives the valve good flow regulation characteristics. Turbulent flow past the seat and plug, when the valve is open, results in a relatively high pressure drop, limited flow capacity, and low recovery. Advantages Efficient and precise throttling  Accurate flow control  Disadvantages Low recovery and relatively low coefficient of flow (Cv).  High pressure drop, higher pump capacity and system wear  More expensive than other valves The sealing device is a plug that offers limited shut-off capabilities, not always meeting bubble tight requirements. Applications requiring Precise flow regulation Frequent and wide throttling operation  Suited to very high pressure dro

Butterfly Valves Applications advantages and disadvantages

  Butterfly Valves Butterfly valves consist of a disc attached to a shaft with bearings used to facilitate rotation. These are considered high recovery valves, since only the disc obstructs the valve flow path. The flow capacity is relatively high and the pressure drop across the valve is relatively low. The butterfly valves are used for limited throttling where a tight shut off is not required. When fully open, the butterfly creates little turbulence or resistance to flow. Best Suited Control Linear Equal percentage  Recommended Uses Fully open/closed or throttling services Frequent operation Minimal fluid trapping in line Applications where small pressure drop is desired  Applicable Standards AWWA C504 for rubber-seated butterfly valves API 609 for lug and wafer type butterfly valves MSS SP-69 for general butterfly valves UL 1091 for safety butterfly valves for fire protection services  Advantages Low cost and maintenance High capacity  Good flow control Low pressure drop  Disadvanta

Ball Valves Applications

  Ball Valves Ball valves are a quick opening valves that give a tight shutoff. When fully open, a ball valve creates little turbulence or resistance to flow. The valve stem rotates a ball which contains an opening. The ball opening can be positioned in the fully open or fully closed position but must not be used to throttle flow as any abrasive wear to the ball will cause leakage when the valve is closed. Ball valves are considered high recovery valves, having a low pressure drop and relatively high flow capacity. Best Suited Control Quick opening Linear Recommended Uses Fully open/closed, limited-throttling Higher temperature fluids  Advantages Low cost  High flow capacity  High pressure/temperature capabilities Low leakage and maintenance  Tight sealing with low torque Easy quarter turn operation- desirable to most operators Fairly easy to automate.  Disadvantages Limited throttling characteristics  Prone to cavitation  Not suitable for slurry applications due to cavities around the

Control Valve question and answers

Control Valve question and answers 1. What is control valve? A power operated device used to modify the fluid flow rate in a process control system. It usually consists of a body or valve and an actuator, which responds to a signal from the controlling system and changes the position of a flow controlling element in the valve. 2. Can two control valves be used in series in high pressure drop applications?  Dropping the pressure across two valves rather than one is theoretically better. However, in practice, the two valves will not usually control well together unless the process can operate with a very low proportional band with slow response times. A better and usually less expensive approach is to use a valve that is designed with multiple pressure drop restrictions inside the trim. 3. What is the valve seat? The valve seat is that the apron for an outlined flow through opening within the valve through that the medium to be regulated needs to flow. 4. What is the valve cone? The valv