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Gate valves control the flow of media by raising the gate (opening) and lowering it (closing). The distinguishing feature of the gate valve is the straight through passage, which causes minimal pressure loss across the valve. Unlike butterfly valves, the gate valve's clear bore also allows a pipe cleaner to pass through during pipe cleaning. Gate valves are available in a variety of options, including various sizes, materials, temperature and pressure ratings, and gate and bonnet designs.
Gate valves tend to be slightly less expensive than ball valves of the same size and quality. They are slower to actuate than right angle rotary valves and are suitable for applications where valve operation is infrequent, such as isolation valves. Gate valves should be used fully open or fully closed, rather than regulating flow. Automatic gate valves exist with electric or pneumatic actuators, but manual gate valves are cost effective because they are used infrequently. (Gate Valves vs. Ball Valves)
The main components of a gate valve are the handwheel, spindle, gasket, bonnet, body, flange and gate. The main operating mechanism is simple and straightforward. Turning the handwheel rotates the stem and moves the gate up or down through the threads. They require more than 360° of rotation to fully open/close the valve. Lift the gate from the flow path and the valve opens. Lowering the gate to its closed position will seal the bore, causing the valve to close completely.
For gate valves, the relationship between gate vertical travel and flow is non-linear, with the greatest change occurring near closure. When used to regulate flow, the relatively high flow rate at partial opening can cause wear on the gate and seat, while the gate may vibrate, thus shortening the valve's life.
Gate valves are available in a variety of designs, each using different technologies to meet the requirements of various applications.
The bonnet protects the internal components of the gate valve. It is screwed or bolted into the valve body to form a leak-proof seal. Therefore, it is removable for repair or maintenance purposes. Depending on the application, the gate valve can have a screw-on, live-joint, bolted, or pressure-sealed bonnet.
Screw-on bonnets are the simplest construction. They are common in small valves and provide a durable, leak-proof seal.
The union cap is held in place by the union nut. The union nut is located on the lower edge of the bonnet and screws into the valve body threads. This type of design ensures that the leak-proof seal created by the nut will not deteriorate with frequent removal of the bonnet. For this reason, live-joint bonnets are common in applications that require periodic inspection or maintenance.
Bolted bonnets provide a seal in larger valves and higher pressure applications. In this type, the bonnet and valve body are flanged and bolted together.
Pressure-sealed gate valves are ideal for high-pressure applications (over 15 MPa). This type of construction uses internal pressure to create a better seal. Pressure-sealed bonnets have a downward-facing cup that is inserted into the valve body. As the internal fluid pressure increases, the cup is forced outward, resulting in an improved seal.
Gates are available in a variety of designs and technologies to provide an effective seal for different applications.
In most gate valves, the gate is wedge-shaped and sits on two angled seats. In addition to the primary force generated by fluid pressure, the high wedging force on the seats created by the tightening of the stem helps to seal. The wedge gate does not stick to the seat at high fluid pressure differentials and has a longer service life because there is less "friction" on the seat.
Gate valves are also available in parallel form, where the gate is flat and the seat is parallel. Parallel gate valves use line pressure and positioning to achieve a tight seal. Parallel gates consist of two parts with a spring in the middle. The spring pushes the parts against the seat to enhance the seal. Due to their inherent design, parallel gate valves offer safety advantages in high temperature applications. In a wedge gate valve, the additional compression load on the seat may result in thermal bonding and restricted opening of the valve due to expansion. In addition, the absence of wedging action in parallel gates results in relatively low closing torque, leading to smaller, less expensive actuators or less manual operation. Because they slide into place, parallel gates keep dirt away from the seating surface.
A slab gate, also known as a straight-through conduit gate, is a one-piece gate that includes an orifice size hole. In the open position, the bore is aligned with two seat rings. This alignment produces a smooth flow with minimal turbulence. This unique design minimizes pressure loss in the system and is ideal for the transportation of crude oil and natural gas liquids (NGLs). The valve seat is kept clean. However, the disc cavity can trap foreign material. As a result, the cavity typically has a built-in plug for maintenance purposes to drain foreign material buildup.
Expansion gate valves have two slab gates matched together to provide a seal by mechanical expansion of the gate. When lifted, both slab pouring ports allow media flow. The upward force on one plate and the stop of the second plate, through a step in the valve body, allows outward mechanical expansion for proper sealing. When closed, the slab gate blocks the media flow and the downward force on one slab (stem) and the upward force (step in the body) allow outward mechanical expansion for proper sealing.
These valves provide an effective seal for both the upstream and downstream seats. This seal makes them ideal for applications such as isolation valves in power plants, shut-off valves in process systems, and high temperature valves in refineries.
Knife gate valves are suitable for viscous fluids and dry bulk solids. The gate has only one piece of metal, usually pointed. These valves are self-cleaning because they pass through the seat each time they open and close.
The door is raised and lowered by the rotation of a threaded stem. A manual wheel or actuator rotates the stem. Depending on the design, the stem is considered raised or non-raised. Therefore, as you rotate the stem, it raises or stays in place as it rotates.
The male thread and yoke (OS&Y), also known as the rising stem, is secured to the door. Therefore, the threads are located on the drive side. Therefore, when the door is raised or lowered, the stem moves up and down with it. As a result, they have built-in visual indicators of valve status and are easy to lubricate. Because they have moving parts, they cannot be used with bevel gears or actuators. Therefore, rising gate valves are suitable for manual actuation.
On the other hand, non-rising stems are fixed to the actuator and screwed into the gate. An indicator is usually screwed onto the stem to indicate the open or closed status of the valve. Non-rising gate valves are common in underground installations and applications where vertical space is limited.
What is a gate valve?
A gate valve controls the flow of media by raising the gate (opening) and lowering the gate (closing).
How does a gate valve work?
By turning the manual handle, the threaded rod moves the gate up and down. As the gate rises, it opens, and as it lowers it closes the media flow.
What is a gate valve used for?
Gate valves are used to open and close the flow control.
Why do we use gate valves?
A gate valve is typically used to completely shut off fluid flow, or to provide full flow in a pipeline in the fully open position. Therefore, it can be used in either the fully closed or fully open position. A gate valve consists of a valve body, seat and flap, spindle, gland and a wheel for operating the valve.
What is the difference between a ball valve and a gate valve?
The main difference is operation. A gate valve moves a solid disc up and down to open/close the orifice. A ball valve rotates the ball (orifice) with the orifice by 90 degrees to open/close the valve.
What is a gate valve in a pipeline?
A gate valve is the most common valve in a water system. It represents a linear motion isolation valve that has the function of stopping or allowing flow. A gate valve gets its name from the closing element that slides into the flow stream to provide closure, thus acting as a gate.
How does a gate valve work?
Gate valves function by lifting a rectangular or circular gate out of the fluid path. When the valve is fully open, the gate valve is full bore, which means there is nothing obstructing the flow because the gate has the same opening as the pipe diameter. This bore also determines the size of the valve.
What is the difference between a gate valve and a globe valve?
Gate valves offer very little resistance to fluid flow in the fully open position, and the pressure drop across the valve is minimal. On the other hand, globe valves have a high pressure drop even in the fully open condition and have a high resistance to fluid flow.
Do gate valves restrict flow?
Gate valves allow the customer to control the rate of flow, e.g. slow drip flow instead of full flow, but not immediate stop.
Do gate valves have gaskets?
Gate valves are a simple valve that, unlike most other types of valves, do not rely on rubber gaskets for sealing. Instead, they use a guide and a "gate" made of metal to stop and start the flow. The multi-turn handle makes operation simple and smooth.
Can I use a ball valve instead of a gate valve?
If you already have a gate valve installed and must replace it, you can certainly replace it with a ball valve. You will need a flashlight to heat the parts and remove them. Turn off the water and drain it out of the pipe and valve. You will also need to open the valve.
How do I know if my gate valve is working?
The gate valve has a knob at the top that raises and lowers the internal gate when turned, hence the name. To open the gate valve, turn the knob counterclockwise and turn it clockwise to close the valve. There is no visual indicator to see if the gate valve is open or closed.
What is a check valve or gate valve first?
A check valve is located between the pump and the gate valve to protect the pump from backflow in the event of an unexpected drive failure. The gate valve should not be located between the check valve and the pump.
What is the service life of a gate valve?
You can expect the service life of a globe valve to be about 10 to 25 years, with an average of 20 years. However, if they are not "exercised" every two years, there is a good chance that the valve will freeze prematurely in the open position when you really need to close it for a pipeline emergency or repair.
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