The wedge is the sealing part of a gate valve and is therefore crucial. Consider the following:
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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 part 1, EN and GSK* requirements is recommended and involves the following:
According to ISO -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 -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.
Gate valves are essential components in various industries, from water treatment to oil and gas, providing a reliable solution for stopping and starting fluid flow. With multiple types, materials, and specifications to consider, ordering the right gate valve can be challenging. This guide will help you navigate the key factors to consider when ordering gate valves, ensuring optimal performance and longevity for your application.
Gate valves come in several types, each designed for specific applications and performance characteristics. The most common types include:
Rising Stem Gate Valves: Ideal for above-ground installations, these valves have a visible stem that rises as the valve opens, providing a clear indication of the valve&#;s position. These are best for applications where valve position needs to be visible, such as in water treatment.
Non-Rising Stem Gate Valves: With a stem that does not extend outward as it opens, these valves are suitable for confined spaces, such as underground installations. They are commonly used in municipal water systems and industrial applications.
Knife Gate Valves: These valves feature a sharp-edged gate that can cut through thicker media, like slurry or viscous fluids. They&#;re commonly used in wastewater treatment and mining operations.
When selecting a gate valve type, consider the space available for installation, the need for visibility of valve position, and the type of media you will be controlling.
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The material of the gate valve body and components is crucial for durability and compatibility with the media being handled. Common materials for gate valves include:
Cast Iron: Affordable and durable, cast iron gate valves are suitable for low-pressure applications such as residential plumbing and water distribution.
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Carbon Steel: Known for strength and resilience, carbon steel valves are ideal for high-pressure and high-temperature applications, including oil and gas pipelines.
Stainless Steel: Resistant to corrosion, stainless steel is suitable for applications involving corrosive media or environments, like chemical processing and marine applications.
Bronze and Brass: Often used in potable water systems, these materials are highly resistant to corrosion and are considered safe for drinking water applications.
Select a material that matches the pressure, temperature, and chemical compatibility requirements of your specific application to ensure long-lasting performance.
Gate valves come with specific pressure and temperature ratings that define their performance limits. The pressure rating indicates the maximum pressure the valve can handle, typically expressed as PSI (pounds per square inch) or PN (pressure nominal). Temperature ratings are also essential, especially for valves used in high-temperature applications like steam processing.
Verify that the valve&#;s pressure and temperature ratings match or exceed the requirements of your application. Using a valve outside its rated limits can lead to premature failure, leaks, or safety hazards.
Proper sizing is critical to ensure that the valve fits seamlessly into your pipeline. Gate valves are usually sized by their nominal diameter, often available in standard sizes such as 1 inch, 2 inches, and so on. Measure the pipe diameter carefully before ordering to prevent installation issues.
Gate valves also come with different connection types, including:
Flanged Connections: Common in larger pipes, flanged connections provide secure, leak-proof seals for high-pressure applications. They are easy to install and replace but require precise alignment during installation.
Threaded Connections: Suitable for smaller pipes, threaded connections are ideal for low-pressure applications. They are simple to install but may not be as durable under high pressure as flanged connections.
Welded Connections: Offering a permanent connection, welded gate valves are used in high-pressure, high-temperature applications where disassembly is not required. These require skilled installation but provide a secure seal.
Select a connection type that meets your application requirements and aligns with your existing pipeline setup for easy installation and maintenance.
Q: What size and material are best for my application?
Consult with your supplier, providing details about your pipeline size, operating pressure, temperature, and the type of media to determine the ideal size and material.
Q: How do I ensure the valve's durability?
Look for gate valves with ratings that meet or exceed your application&#;s specifications. Choosing the right material and checking for certified pressure and temperature ratings can help maximize durability.
Q: Are gate valves suitable for throttling?
No, gate valves are not recommended for throttling as they are designed for full open or full close positions. Throttling can damage the valve gate and reduce its lifespan.
Q: Do I need a rising stem or non-rising stem gate valve?
If you need visual confirmation of the valve&#;s position, a rising stem valve is best. For confined spaces, a non-rising stem valve may be more appropriate.
By following these guidelines and asking the right questions, you can confidently order the gate valve that meets your operational needs and ensures reliable performance. Always work with a reputable supplier to get high-quality gate valves that suit your industry standards.
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