A gate valve, often referred to as a sluice valve, opens by raising a barrier (gate) out of the fluid. Gate valves rarely restrict fluid flow when the gate is completely open and take up very little room along the pipe axis.
In pipe systems, the gate valve is likely the most used valve. This general service valve is mostly used for non-throttling and on-off applications. Well, in this reading, we’ll explore gate valves, their functions, applications, parts, diagrams, types, and how they work. We’ll also discuss its advantages and disadvantages.
Let’s begin!
What is Gate Valve?
A gate valve is often referred to as a sluice valve. It opens by raising a barrier (gate) out of the fluid. Gate valves barely impede fluid flow when the gate is completely open and take up very little space along the pipe axis.
In order to exert pressure on the sealing surface, the gate faces are often wedge-shaped; however, they can be parallel.
By raising the gate (open) and lowering it (closed), a gate valve controls the flow of the media. The unique characteristic of a gate valve is its unobstructed, straight-through path, which results in low-pressure loss across the valve.
Gate valves should not be used to control flow; instead, they should be used fully open or closed. Although there are automated gate valves with pneumatic or electric actuators, manual gate valves are more affordable since they are used less frequently.
Compared to ball valves of the same size and quality, gate valves are often a little less expensive. They are used for isolating valves and other applications where valve activity occurs rarely, and they actuate more slowly than quarter-turn valves.
In contrast to butterfly valves, a gate valve’s unobstructed bore permits a pig’s passage during pipe cleaning processes. Gate valves come in a wide range of sizes, materials, pressure and temperature ratings, and gate and bonnet designs.
Related: What is Ball Valve? its Diagram and How it Works
Applications
Below are the uses of gate valves across various industries:
- Used to completely shut off fluid flow or provide full flow in a pipeline.
- Used in fully closed or entirely open positions.
- Not used for flow regulation.
- Typically has no obstruction in the flow path, resulting in low flow resistance.
- The open flow path varies nonlinearly with gate movement, causing an uneven flow rate change.
- Mostly used with larger pipe diameters due to less complex construction.
Parts and Construction of Gate Valves
The major parts of a gate include a handwheel, spindle, gasket, bonnet, pressure seal bonnet, flange, and knife gate valve.
In the construction of a gate valve, a threaded stem that joins the actuator (such as a motor or handwheel) to the gate. This is what activates gate valves.
Depending on which end of the stem is threaded, they are classified as either having a rising or non-rising stem.
A visible indicator of valve position is provided by rising stems that are fastened to the gate and rise and lower concurrently when the valve is actuated. To move the threaded stem, the actuator is attached to a nut that is turned around.
Non-rising stem valves are threaded into the gate, secured to the actuator, and rotate with it.
Since the motion of the gate is hidden inside the valve, they could have a pointer threaded onto the stem to show the valve position. When there is a shortage of vertical space, non-rising stems are ideal.
The flanged ends of gate valves can be drilled in accordance with flange dimension requirements that are compatible with pipelines.
Cast iron, cast carbon steel, ductile iron, gunmetal, stainless steel, alloy steels, and forged steel are commonly used to create gate valves. Ultra-high vacuum chambers feature gate valves made entirely of metal to separate different areas of the chamber.
Diagram
What are the Types of Gate Valve?
The various types of gate valves include solid taper wedge, flexible wedge, and split wedge or parallel disc valves.
Solid Taper Wedge
The most popular and widely used disc type is a solid wedge because of its robustness and ease of usage. Almost any fluid may be used with a solid wedge valve, which can be fitted in any position. It can also be used for turbulent flow.
However, it cannot make up for variations in seat alignment brought on by thermal expansion or pipe stresses. This kind of disc design is the most prone to leaks. When employed in high-temperature operation, a solid wedge is susceptible to thermal locking.
A situation named “thermal locking” occurs when the metal expands and becomes trapped between the seats. Applications involving moderate to lower pressure and temperature often employ solid-wedge gate valves.
Flexible Wedge
The flexible wedge is a solid disc with a perimeter incision. These incisions vary in size, shape, and depth. A shallow, narrow wedge perimeter cut reduces flexibility but keeps strength.
A cast-in recess or deeper and broader wedge perimeter cut increases flexibility but weakens.
This design enhances seat alignment and leak tightness. It also increased thermal binding performance. Flexible wedges is a gate valve used in steam systems.
Thermal expansion of steam lines can deform valve bodies, causing thermal vision loss. The flexible gate reduces thermal blindness by bending as the valve seat compresses due to steam pipeline thermal expansion.
Split Wedge or Parallel Disks Valve
Wedge split is a unique mechanism that binds the two solid disc sections together. If half the disc is out of alignment, it can adapt to the sitting surface. The split disc might be wedged or parallel.
Spring-loaded parallel discs seal both ways and are always in contact with seats. The split wedge handles noncondensing gases and liquids at normal and high temperatures.
Even if the valve is closed on a cold line, disc movement prevents thermal binding. This implies that fluid heating and expanding a line do not cause thermal blindness.
How Does a Gate Valve Work?
The handwheel, spindle, gasket, bonnet, valve body, flange, and gate are the primary parts of a gate valve. The main mechanism of working is simple. The stem spins when the handwheel is turned, and the threads move the gate up or down.
To fully open or close the valve, they need to be rotated 360 degrees. The valve opens by raising the gate out of the flow’s path. The valve fully closes when the gate is lowered to its closed position, closing the bore.
A gate valve’s vertical movement and flow rate have a nonlinear relationship, with the largest variations happening close to shutdown.
When used to control flow, the relatively high flow velocity during partial opening causes wear on the gate and seat, which, in addition to potential gate vibrations, reduces the valve’s lifespan.
Related: What is Needle Valve? its Diagram and How it Works
Advantages and Disadvantages of a Gate Valve
Advantages:
- Low Fluid Resistance: The straight-through shape allows fluid to pass through the valve with minimal resistance.
- Superior Sealing Performance: Faster opening and closing mechanism than shut-off valves.
- Wide Application Range: Versatile and suitable for applications with mediums like steam, oil, granular solids, high-viscosity mediums, venting valves, and low-vacuum system valves.
- Bidirectional: Dual flow directions, suitable for pipelines with changing flow directions.
Disadvantages:
- Slow Opening & Closing: Long opening and closing time due to the need for lifting and falling valve plates.
- Scratches: Excess friction between the valve plate and sealing surfaces can cause scratches, impacting sealing performance and service life.
FAQs
What is a gate valve used for?
A gate valve is generally used to completely shut off fluid flow or, in the fully open position, provide full flow in a pipeline. Thus it is used either in the fully closed or fully open positions.
Which are the 2 basic types of gate valves?
The two main types of gate valves are wedge-shaped and parallel. Wedge-shaped gate valves (including solid taper wedge, flexible wedge and split wedge designs) use two inclined seats and an inclined gate or barrier, which is intentionally slightly misaligned with the seats.
Why use a gate valve instead of a ball valve?
Ball valves create a reliable, tight seal, so they can be used with both liquids and gases. Gate valves are better suited for thick liquids (like oil) since they are more prone to leaking.
What is the difference between a gate valve and a globe valve?
Both gate valves and globe valves can operate as on/off valves. A gate valve is not meant to be used to throttle flow, but a globe valve can. Flow diverts within the globe valve and becomes parallel to the valve seat. This design makes globe valves efficient flow throttlers.
What is another name for a globe valve?
Even though globe valves exhibit more pressure drops than gate valves, you can use them where the pressure drop via the valve is a non-controlling factor. Another name for globe valves is throttle valves when they are used for throttling purposes.