The basic explanation is that actuators move your control valves to a certain desired position by using an outside power source. There are different types of valve actuators, but they all are responsible for performing the following functions.
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They must move the Control valve closure member to the position you want. The Control valve closure member is made of up the plug, disc, or ball. The actuator needs to create enough torque to move these things even under severe conditions.
The actuator also needs to be able to hold the control valve closure in the position you desire. This means it needs enough fluid power or spring to take on the dynamic torque that throttling applications create.
The actuator must seat the member with enough torque to ensure the shutoff specification. Actuators should also provide a solution in the event of system failure, like springs or battery power. Their failure positions can be either open or closed. Your actuator needs to be regulated to provide enough operating speed and provide enough rotational travel.
Traditional valve actuators were essentially a geared motor with position sensing switches. Modern-day valve actuators have more advanced capabilities. They not only perform functions of opening and closing valves but can also check on the functional status and wellbeing of a valve as well as offer predictive maintenance data.
Some physical locations are hazardous or precarious to human beings. In these circumstances, an automated controlling device can mitigate the risk to the individuals involved. In some situations, critical valves need to be controlled in situations of emergency circumstances.
The Control valve actuator can reduce the risk of serious environmental mishaps as well as to mitigate damages caused in such situations. When some processes require high pressure and large line sizes, the load of power needed to operate a valve can be very high. In these conditions, the intensified mechanical advantage and usage of high output motors can facilitate easy operation of large valves.
There are four main types of actuators:
Is the most common form of actuation method. Pneumatic Actuators are highly effective, simple to use, inexpensive when compared to other forms of actuation methods. Reliable, inexpensive to maintain and generally have an extended operating life.
This is also a ommon and widespread actuator used. The primary advantage of this type of actuator is that all accessories are included in the package and are physically and environmentally safeguarded. It has all the basic functions integrated in a compact housing which can be watertight, explosion proof and in most circumstances, submersible.
Like Electric Multi-Turn Actuators, these actuators are compact in nature and are ideal for smaller valves.
These forms of actuators are recurrently used when multi-turn output is needed to control a linear type of valve, for example, a gate or globe valve. In normal circumstances, electric actuators are used for this type of valve. Although, if there is no electric power supply available to use, then Pneumatic or Hydraulic motors can be utilised to operate multi-turn actuators.
For Quarter-turn actuation, as automation is growing across industries, physical work is being gradually phased out by technology and automatic controls. The importance of valve actuators to develop an interface between the control and the physical action of a valve has increased. There is a critical need for safe working conditions and process safety that valve actuators can offer.
These Actuators, which function on hydraulics are extremely dynamic. The primary factor attributing this is they can be utilised wherever there is no readily available source of electricity or power.
The MASCOT Spring Cylinder Linear Actuator is a powerful, high-performance pneumatic actuator that provides positive throttling or on-off operation for automatic control valves. The positioner and most sized cylinders are designed for supply pressures up to 150 psi, making very high thrusts attainable in a compact unit.
This actuator is fully field reversible for air-to-open or air-to-close action without additional parts; a spring provides fail-safe operation. The positioner supplies air to both sides of the piston, providing exceptionally stiff, precise movement together with very high frequency response.
The MASCOT Spring Cylinder Rotary Actuator combines high torque and pneumatic stiffness with excellent throttling capabilities. These characteristics are designed into a lightweight, rugged, and compact assembly, making the MASCOT rotary actuator the first choice for quarter turn applications. The MASCOT rotary actuator is designed to operate the DISKFLO high performance butterfly valve, the VFLO V-notch ball valve, or other applications requiring precise rotary motion. MASCOT pneumatic and electro-pneumatic positioners are available for throttling applications.
The actuator, cylinder and MASCOT positioner are designed for supply pressures up to 150 psi, making very high torques attainable. The actuator uses a rocking piston for direct conversion of linear motion to rotary motion. The rocking piston assembly combined with a splined shaft and lever eliminates lost motion.
Electric valve actuators can make fluid systems safer and easier to control. They’re especially useful if you need to expand or upgrade your system and make it more complex.
Here are some parameters that can help guide your decision:
If you need help deciding which kind of actuator you need, get in touch with our engineers today and we can help you decide.
MASCOT Industrial engineers have over 25 years of experience in providing high quality equipment to the Global Continuous Process Control Industry. Our core products and services include control valves, choke valves, actuated and commodity valves, and associated equipment for both standard and severe service applications.
MASCOT’s Engineering & Manufacturing expertise allows us to provide tailored solutions to our customers’ needs with timeliness and accuracy no matter the process. We aim to exceed our expectations with Better Value highly engineered products, faster delivery (-times) on any process, offering support from first contact through to after-sales and beyond.
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The wedge is the sealing part of a gate valve and is therefore crucial. Consider the following:
The wedge nut connects the wedge to the stem. There are two basic wedge nut designs; A loose wedge nut design where the brass nut slides in a slot in the wedge core, and a fixed wedge nut design where the nut is expanded in the wedge core. With a fixed wedge nut design the number of movable parts is reduced, thus eliminating the risk of corrosion as a result of moving parts damaging the rubber surface of the wedge core. A fixed wedge nut design is therefore recommended.
The wedge is exposed to friction and stress forces when the valve is opened and closed during operation of the pipeline. Guides in the wedge fitting to corresponding grooves in the body help stabilizing the wedge position during operation and ensure that the stem does not bend downstream due to the flow velocity. Wedge shoes help ensuring that the rubber on the wedge surface is not worn through as a result of the friction between the wedge and the guiderail in the body. Make sure that the wedge shoes are fixed to the wedge and that the rubber layer underneath is sufficient to prevent corrosion of the wedge core.
It is vital for the tightness of the valve that the wedge is fully vulcanized with rubber and that the rubber volume on the sealing area of the wedge is sufficient to absorb impurities in the seat. A strong bonding between the rubber and the wedge core is important to ensure a correct seal even when the rubber is compressed, and to prevent creeping corrosion even if a sharp object penetrates the rubber during closing of the valve.
The rubber quality is critical for the durability as well as for the valve function. The rubber must be able to withstand continuous impact from impurities and chemicals without being damaged and it must be able to absorb small impurities in the seat to close tight. Consider the following:
The compression set means the rubber’s ability to regain its original shape after having been compressed. The EN 681-1 standard states the minimum requirements for the compression set value, but the better the compression set, the better is the rubber’s ability to regain its shape and close 100% tight year after year.
Organic substances migrate from the rubber compound and act as nutrients for microorganisms, which will then start forming biofilm causing contamination of the drinking water. Select valves with a wedge rubber that ensures minimum formation of biofilm.
Chlorine and other chemicals are commonly used to clean new pipelines or disinfect old ones. Ozone and chlorine may also be added in low concentrations to make the water drinkable. The rubber compound must not degrade or crack as a result of chemical treatment of the drinking water, as it would cause corrosion of the wedge core.
All rubber components in contact with the drinking water should carry a drinking water approval. If no local approvals are required, the rubber in direct contact with the drinking water should hold one of the major approvals like DVGW/KTW, KIWA or NF.
The external corrosion protection is critical for the service life of the valve. A uniform and even epoxy coating in compliance with DIN 3476 part 1, EN 14901 and GSK* requirements is recommended and involves the following:
According to ISO 12944-4.
Min. 250 μm on all areas.
The curing of the epoxy coating is to be checked in a cross linkage test (MIBK test). One drop of methyl isobutyl ketone is put on a test piece. After 30 seconds the test area is wiped with a clean white cloth. The test surface may not become matt or smeared, and the cloth must remain clean.
A stainless steel cylinder is dropped on the coated surface through a one meter long tube. After each impact the component is to be electrically tested, and no electrical breakthrough shall occur.
A 3kV detector with a brush electrode is used to reveal and locate any pinholes in the coating.
There are two important design issues:
The sealing placed in the bonnet around the stem retaining the pressure inside the valve/pipeline. Stem sealings should always be designed to be maintenance-free and should last the service life of the valve or at least fulfil the service life demands according to EN 1074-2. The main seal retaining the inside pressure should preferably be designed as a hydraulic seal giving tighter seal with increased internal pressure. Backup seals should be placed around the stem. To protect the sealings against contamination from outside, a sealing should be placed around the stem on the top. For safety and health reasons a drinking water approved high quality EPDM rubber compound must be used where direct contact to drinking water occurs.
Tightness between the bonnet and the body can be obtained by using a gasket embedded in a recess in the valve. This design ensures that the gasket will remain correctly positioned and not be blown out as a result of pressure surges. To protect the bonnet bolts against corrosion the bonnet gasket should encircle the bolts, and the bolts should be embedded in the valve in such a way that no threads are exposed to the surroundings.
When operating a gate valve either by handwheel or by means of an electric actuator it is important to pay attention to the operating and closing torque.
The torque needed to operate the valve from the open position to the closed position, should be between 5 Nm and 30 Nm depending on the valve size. It is important to consider that valves having an operating torque less than 5 Nm encourages the operator of the valve to close the valve to fast thus risking water hammer and pressure surges in the pipeline.
The torque needed to close the valve to a drop tight position. This torque should for handwheel operated valves be balanced against the handwheel diameter in such a way that it does not present the operator with a rim-force in excess of 30-40 kg. When operating the valve with an electric actuator or manual gearbox the torque should be within the limits of a standard range actuator. It is important to notice that the actuators normally have a torque range that is quite wide, and often it is the ISO flange connection between valve and actuator that determines the actuator choice. As a main rule valves with ISO flange connection should have max. closing torques as stated below:
To enable the use of pipe cleaning devices the inside diameter of the valves should correspond to the nominal size of the valve.
* GSK stands for Gütegemeinshaft Schwerer Korrosionsschutz, and is an independent quality association with about 30 members, all leading European valve and fittings manufacturers. GSK outlines requirements for the coating itself and for the control procedures of the finished coating.
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