Gate Valves: Rising Stem Gate Valves & Non-Rising
Gate Valves: Purpose & Functionality
Gate valves are useful for fully open and fully closed service functions. Ideal for installation in pipelines as isolation components, the valve opens when lifting a gate out of the pathway of the fluid and closes when the gate returns to its position. However, they are not an appropriate component for controlling or regulating flow in valves.
Compact in design, gate valves require little space along the pipe axis and don’t restrict the flow when the gate is opened fully. They are also known as multi-turn valves and operate either clockwise to close or clockwise to open the rotating motion of the threaded stem.
- Compact design
- Lower cost point than ball valves
- Available in many sizes, materials, temperature and pressure ratings, and gate and bonnet designs
- Little resistance to flow
Gate Valve Applications
Suitable for above-ground and underground installation, gate valves are useful in a wide variety of applications. Choosing the correct valve dependent on its application is vital, so there are no high replacement costs. Gate valves are often used when minimum pressure loss and a free bore are needed.
They’re suitable for the following disciplines:
- General industrial
- Water treatment and distribution (WRAS)
- Compressed air and oil
Types of Gate Valves
Gate valves have different kinds of characteristics that are useful for various applications, but the two main types are parallel and wedge-shaped.
Parallel Gate Valves
Compact in its structure, with reliable closing and sealing performance, a parallel gate valve uses a flat gate between two parallel seats. Mainly used in the chemical, petroleum and natural gas field, it’s the ideal valve to provide isolation when closed.
Wedge-shaped Gate Valves
Wedge-shaped gate valves feature a disc that is in the shape of a wedge that seats between two inclined seats. Used in high flow or aggressive applications, it minimizes the vibration and chatter of the valve.
Rising Stem & Non-rising Stem Gate Valves
Made from a range of materials, their characterization can be seen by their rising or non-rising stem. A rising stem gate valve is only useful for above-ground installation. The stem fixes to the gate, and as it rises and lowers during operation, it indicates the valve position and the possibility to grease the stem. Suitable for both above-ground and underground installations, non-rising stems are embedded onto the gate, rotating with the wedge rising and lowering inside the valve. It’s ideal for a valve with limited space as they are more compact in design.
Rising Stem Gate Valve Advantages
- Easy to open and close.
- Small fluid resistance.
- Medium flow is not restricted.
- Easy to spot valve opening position by looking at the amount of stem that is exposed.
Types of Gate Valve Material:
Gate valves come in a variety of different materials depending on the environment and application used. You can choose from the following materials:
- Cast Iron
- Ductile iron
- Stainless steel
- Carbon steel
- Exotic alloys
Wedge Gate Valve Advantages
- Flow resistance is small.
- Media can flow in any direction on both sides of the wedge gate valve.
- Easy to install.
- Face to face dimension of a wedge gate valve is small.
- Compact structure.
- Long service life.
- Sealing surface made of stainless steel and hard alloy results in a rigid design.
- Suitable for a wide range of applications.
Wedge Gate Valve Disadvantages
- Maintenance is difficult.
- The type of sealing surfaces can quickly cause erosion and scratches.
- Large in size.
- It takes a long time to open and close.
- A wedge gate valve’s structure is more complicated.
What are gate valves used for?
Generally, gate valves are used to completely shut off fluid flow or provide full flow in a pipeline. They are installed in pipelines as isolation valves and perform by moving clockwise to close or clockwise to open along the stem. They function in the fully closed or fully open positions and consist of a valve body, seat and disc, a spindle, gland, and a wheel for operating the valve.
What are the different types of gate valves?
There are three ways to classify a gate valve, by the type of disk, body bonnet joint and stem movement.
Types of disk include:
- Solid taper wedge
- Flexible wedge
- Split wedge or Parallel disks Valve
Types of Body Bonnet Joint include:
- Screwed Bonnet
- Pressure-Seal Bonnet
Types of Stem movement include:
- Rising Stem
- Non-rising Stem
What is the difference between a ball valve and a gate valve?
They both essentially serve the same function, however, the main difference is in the operation. While gate valves open by lifting a round or rectangular gate out of the path of the fluid, ball valves have a stem and a ball that turn horizontally.
Why do gate valves fail?
Wear and corrosion are the most common cause of a faulty gate valve. They can wear out over time, with corrosion causing the disc to stick in either the open or closed position. If the handle is forced, it usually leads to the stem breaking and making the valve useless.
How does a rising stem gate valve work?
Rising stem gate valves have threads external to the valve body and are usually cast or forged steel. They operate by pushing and pulling the valve stem. They are threaded and matched to a stem nut that converts the rotational motion into linear movement of the valve stem. It works by the gate valve stem moving up when the valve is opening.
What is a non-rising gate valve?
A non-rising gate stem in a gate valve means the stem will turn to open and close the gate, but the stem does not move up or down as it turns. A non-rising stem gate valve takes up a small amount of space to operate, and the design allows the stem of the gate valve to be fully open when the handle is rotated to the left and fully closed when the handle is turned to the right.
What’s the difference between a rising stem gate valve and a non-rising stem gate valve?
There are two main ways to differentiate between a rising stem gate valve and a non-rising stem gate valve. The first is appearance; rising stem gate valves are typically made from cast or forged steel, while non-rising stem gate valves are usually brass, bronze, or cast iron. There is also a difference in size; non-rising takes up less space, whereas the rising type requires more space. The second is the ascension of the valve stem. It’s easy to spot whether the valve is closed or open on a rising stem gate valve by looking at the amount of stem that is exposed; if it is a lot, the valve is open. Whereas the stem of the non-rising stem gate valve only rotates and does not move up and down.
How does a wedge gate valve work?
A wedge gate valve works by inserting a rectangular wedge into the fluid flow. It’s primarily used for on/off non-throttling services. It works by a barrier lifting away from the flow path. They have a sealing element in the shape of a wedge, and the wedge expands from both sides due to the stem force to ensure proper sealing. They are engineered with a tapered gate with metal-to-metal sealing to ensure a rigid design.
What is a flex wedge gate valve?
Flex or flexible wedge gate valves feature a one-piece disc with a cut around the perimeter to improve the ability to correct mistakes or changes in the angle between the seats. A shallow cut gives a little flexibility but retains the valve strength.
What is a resilient wedge gate valve?
A resilient wedge gate valve incorporates a fully rubber-sealed wedge to prevent the buildup of sand and sediment. Prevention of this is essential, as they can cause seal erosion on metal-seated gate valves. Therefore, they are primarily used for water-based or sewer system applications.