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Gate valves come in various types, each with different applications. Therefore, it is crucial to select the appropriate type when purchasing, as improper installation can lead to leaks and damage. Understanding the different types of gate valves is essential.
The main types of gate valves include: wedge gate valves, parallel sliding gate valves, flat gate valves, knife gate valves, rising stem gate valves, and non-rising stem gate valves. These differ in their bonnets, end connections, and operating methods. In short, there are certain distinctions between them.
The following will introduce each type of gate valve.
How Are Gate Valve Types Classified?
The classification of gate valves is relatively complex and cannot be based on a single characteristic; there is overlap in classification.
Different valves may have different valve stems, bonnets, etc., resulting in different classifications.
The following are some classifications of gate valves:
| Classification Basis | Common Gate Valve Types |
|---|---|
| Gate design | Wedge, parallel slide, slab, knife |
| Stem design | Rising stem, non-rising stem |
| Bonnet design | Bolted bonnet, welded bonnet, pressure-seal bonnet |
| End connection | Flanged, butt-welded, threaded |
| Operating method | Handwheel, gearbox, electric, pneumatic, hydraulic |
What Is a Wedge Gate Valve?
A wedge gate valve is a type of gate valve and is quite common in industrial systems. One characteristic of this type of gate valve is its inclined sealing surface, which is movable and mates with the valve seat.
When the valve is closed, the wedge moves downwards, pressing against the valve seat. This ensures a tight seal.
The wedge gate valve retains the characteristics of a gate valve, being a fully open and fully closed isolating valve. It can be used for water, steam, oil, natural gas, etc.
In industrial systems, ASTM A216 WCB carbon steel is commonly used. However, if corrosion resistance is required, ASTM A351 CF8 and CF8M should be preferred.
If a wedge gate valve is used for flow control for extended periods, it can lead to a compromised seal and leakage.
Therefore, the following should be considered when purchasing:
- The structure of the wedge gate valve
- The material properties of the valve seat
- The material and properties of the valve stem
- The pressure rating it can withstand
- The material of the integral gate valve
- The torque of the wedge gate valve
- Production standards and testing
What Is a Solid Wedge Gate Valve?
A solid wedge gate valve is a one-piece rigid wedge.
It has a simple structure but high mechanical strength. The wedge-shaped sealing surface is machined to match the inclined valve seat within the valve body.
Solid wedge gate valves are often used in environments with large temperature variations, pipeline deformation, or limited valve seat misalignment, providing relatively stable operating conditions.
The rigidity of the wedge allows its expansion to compensate for the angular difference between the two valve seats. However, at extremely high temperatures, this may increase the risk of thermal adhesion.
The production of wedge gate valves requires strict control, demanding precise control of the wedge angle, alignment, and surface finish.
What is a Flexible Wedge Gate Valve?
A flexible wedge gate valve is also a one-piece gate valve. However, unlike other gate valves, it has a groove or flexible section, allowing limited movement between the two sealing surfaces.
This mobility effectively adapts to the thermal expansion properties at extremely high temperatures, thereby improving its sealing performance.
This product is often used in high-temperature systems such as steam systems and thermal process piping systems.
However, the production of the groove requires even greater precision, including its shape, thickness, material strength, and surface finish.
What Is a Parallel Slide Gate Valve?
A parallel slide gate valve has a flat sealing surface.
Its structure utilizes two separate valve discs, a diffuser mechanism, and a spring.
Because of its parallel sealing surface, it is not well-suited for high-temperature piping systems.
| Feature | Wedge Gate Valve | Parallel Slide Gate Valve |
|---|---|---|
| Sealing geometry | Angled wedge surfaces | Parallel sealing surfaces |
| Closing action | Mechanical wedging | Sliding and pressure-assisted contact |
| Thermal binding risk | Depends on wedge design | Often lower in suitable designs |
| Typical duty | General industrial isolation | Thermal-cycle or high-pressure service |
| Buyer focus | Wedge angle and seat fit | Disc arrangement and sealing mechanism |
What Is a Slab Gate Valve?
The gate of a slab gate valve has parallel sides, and the opening and closing are perpendicular to the valve body.
Most slab gate valves are designed for full bore, allowing straight passage through steel pipes. When fully open, it is flush with the pipe, creating no resistance during flow.
This type of gate valve is commonly used in oil and gas transportation.
Slab gate valves are often referred to as standard wedge gate valves. Their design offers superior sealing.
What Is a Knife Gate Valve?
A knife gate valve is designed with relatively thin blades that move in the flow path to control its opening and closing.
One characteristic of this type of gate valve is that the thin blades can cut through solid or other particulate matter that enters during flow. Therefore, this type of gate valve is often used in industries such as wastewater treatment, mining, and pulp and paper making.
Knife gate valves are available in unidirectional and bidirectional designs due to their blade and lug design.
Knife gate valves also differ from wedge gate valves in their pressure ratings and sealing performance.
When purchasing knife gate valves, buyers should pay attention to the following aspects:
- Maximum differential pressure
- Seating direction
- Solid concentration
- Blade material
- Elastomer or metal seat material
- Temperature limit
- Required actuator thrust
- Covered or uncovered structure
What Is a Rising-Stem Gate Valve?
A rising-stem gate valve is one in which the valve stem rises when the valve is opened.
The advantage is that it is easy to see whether the valve is open, as the height of the valve stem is immediately apparent.
The stem thread in a rising-stem gate valve is outside the main flow area. This ensures good lubrication.
This type of product requires sufficient height space for installation because the valve stem stroke, handwheel, gearbox, or actuator are all on a horizontal line, thus requiring a certain level of operating space.
| Feature | Rising Stem | Non-Rising Stem |
|---|---|---|
| External stem movement | Rises during opening | Remains at nearly fixed height |
| Position indication | Easy to observe | Usually needs a separate indicator |
| Vertical clearance | Higher | Lower |
| Stem thread location | Often outside the medium | Commonly inside the valve |
| Maintenance access | Generally easier | Depends on internal condition |
What Is a Non-Rising-Stem Gate Valve?
A non-rising-stem gate valve does not raise its stem when open.
It opens by rotating the stem, causing the internal threads in the valve body to lift the gate, thus opening the valve. This type is more suitable for confined environments.
Since the threads are inside the valve body, corrosion or deposits in the fluid can affect them.
When purchasing a non-rising-stem gate valve, pay attention to its material, stem material, thread design, and corrosion resistance.
What Are Bolted, Welded, and Pressure-Seal Bonnet Gate Valves?
These are three different types of gate valves.
Bolted-Bonnet Gate Valve
This type uses bolts and nuts to connect the bonnet to the valve body.
Bolted bonnet gate valves are often used in low-pressure industrial systems.
Welded-Bonnet Gate Valve
A welded bonnet gate valve has the bonnet permanently welded to the valve body.
This type of gate valve is less convenient for maintenance. However, it also reduces the risk of leakage, as disassembly is more cumbersome.
Pressure-Seal Bonnet Gate Valve
Pressure-sealed bonnet gate valves increase the sealing force on the sealing ring through internal pressure.
These gate valves are mostly used in high-temperature, high-pressure system pipelines.
What Are Flanged, Butt-Welded, and Threaded Gate Valves?
They are different connection methods.
Flanged Gate Valve
Flanged gate valves are connected between pipes using bolts and nuts.
This type of gate valve is easier to disassemble and maintain. However, when purchasing, pay more attention to its flange standard and pressure rating.
Butt-Welded Gate Valve
This type of gate valve is directly welded to the pipeline.
Welding provides better sealing and reduces the risk of leakage. It is mostly used in high-pressure, high-temperature systems.
Threaded Gate Valve
The threads used in these valves are often NPT, BSP, etc.
Mainly used in small-diameter piping systems.
What Types of Gate Valve Operators Are Available?
Gate valve operators are available in the following types:
| Operator Type | Typical Selection Condition |
|---|---|
| Handwheel | Smaller valves and moderate torque |
| Gearbox | Larger valves or higher operating torque |
| Electric actuator | Remote operation and automation |
| Pneumatic actuator | Automated duty where air is available |
| Hydraulic actuator | High-thrust or specialized service |
The specific choice depends on the torque and whether it is automated.
Which Gate Valve Materials Are Common for Industrial Use?
Carbon steel and stainless steel are common raw materials for industrial gate valves.
| Component | Common Material Consideration |
|---|---|
| Body and bonnet | ASTM A216 WCB, ASTM A351 CF8 or CF8M |
| Gate | Base material with corrosion-resistant or hardfaced sealing surfaces |
| Seat rings | Stainless steel or hardfaced alloy |
| Stem | Stainless steel or alloy steel |
| Packing | Flexible graphite, PTFE, or engineered packing |
| Gasket | Spiral-wound, graphite, or pressure-seal ring |
| Bolting | Selected for pressure, temperature, and corrosion conditions |
The specific material selection depends on the specific application.
How Should Buyers Choose the Correct Gate Valve Type?
The following table provides some selection guidelines:
| Service Requirement | Commonly Considered Gate Valve Type |
|---|---|
| General industrial isolation | Wedge gate valve |
| Thermal-cycle service | Flexible wedge or suitable parallel slide design |
| Full-bore pipeline | Slab or through-conduit gate valve |
| Slurry or fibrous medium | Knife gate valve |
| Visible position indication | Rising-stem gate valve |
| Limited vertical space | Non-rising-stem gate valve |
| High-pressure steam | Pressure-seal bonnet design |
| Critical welded pipeline | Butt-welded gate valve |
If you are unsure, you can refer to the items in the table above when making your selection.
What Should Buyers Verify Before Ordering?
When purchasing gate valves, consider the following:
- Valve type and internal design
- Nominal size and pressure rating
- Body, cover, gate, seat, and stem materials
- Rising or non-rising stem
- Hood structure
- Ending standard
- Face-to-face dimensions
- Seal hardening
- Operator type
- Pressure and leakage testing
- General layout drawing
- Bill of materials
- Material certificates
- Inspection and test reports
Summary
The above is a classification and detailed introduction of gate valves. Hopefully, this will help you understand the different types of gate valves when making your selection. Therefore, whether it’s a wedge gate valve, parallel sliding gate valve, flat gate valve, knife gate valve, rising stem gate valve, or non-rising stem gate valve, each has its unique characteristics.
