Gate valves and globe valves are two of the most common valves used in industrial applications. Both contribute greatly to any industrial services. They may look alike but these valves function differently. In this article, you will know what makes the gate and globe individually unique as well as the major differences between the two valves.
Gate Valve is a linear valve that uses a wedge shape gate to shut the pipe. The valve is only made to stop or open the flow of fluids in a pipe. One must not use it to control the flow of fluids. Gate valves are best for the conditions where the fluid flows without any restrictions and works well in high pressure and high-temperature situations. But the gate valve is typically used in states where simple on-off control is required. The valve produces minimal resistance against the flow as the gate occupies tiny space in the pipe.
Components of gate valve
There are four primary components of a gate valve.
1. Gate
The gate valve gets its name from this gate. The gate is responsible to effectively seal the pipe to stop or open the flow of fluid. There are many types of gates in gate valves; the type of gate totally depends upon the application of the gate valve. Some common type of gates are
Parallel Slide gate (Use in high temperature and high-pressure lines to prevent thermal binding)
Slab Gate (It is used for transporting Crude oil)
Knife Gate (used in chemical plants, wastewater treatment plants, cement plants etc.)
Parallel Expanding Gate.
2. Stem
The stem is an essential component; it is responsible for raising and lowering the gate. The stem is a threaded rod on which a wheel is spun to raise or lower the gate. There are two types of stems.
Rising stem in this the stem rise over the rotating wheel when opened. The other one is the Non-Rising stem in this the stem rise upwards when opened.
3. Bonnet
Bonnet tightly closes the gate and prevents the fluid from leaking. The bonnet supports the gate to seal the gate tightly. There are four types of bonnets.
Screw-in Bonnets
Union Bonnets.
Bolted Bonnets.
Pressure seal Bonnets.
4. Seat
The seat comes in two configurations Integral part and Ring Construction. The integral part is made from the same material as the valve body while the ring construction the seat thread or press into the position and then welded to seal into the valve body.
Working of gate valve
Gate valves come in several different sizes, materials, designs and temperature and pressure ratings. But the working of a gate valve is straightforward. We rotate the wheel anti-clockwise to lift the gate and clockwise to lower or close the gate to open the valve. Semi-open gate valve is at a very high risk of damage due to throttling, that’s why it’s always preferred to use the gate valve in a fully open or fully close condition.
Globe Valve is also a linear motion valve that uses a ball type or needle type disc to shut the pipe. This valve can stop, start and control the flow of fluids from the pipe. In the globe valve, the disk can completely close and open the pipe or partially close the open to control the flow. When the valve open or close the disc moves perpendicular to the seat, which allows the valve to handle throttling in a better way, which is necessary to control the flow.
Perpendicular attachment of seat and disc form a robust seal hence reduce the risk of leakage.
Components of globe valves
There are five components of a globe valve.
1. Disc
The disc is the component that stops, starts, and controls the flow. It is attached to the stem which lower and rises the disc. There are three types of disc for a globe valve.
Ball Disc – Used in low pressure and low-temperature situations. Can handle throttling but it affects the performance of the disk.
Composition Disc – Made from a rigid non-metallic ring on the disc for an extra tight seal. This type of disk is used in steam and hot water applications.
Plug Disc – Used where extra throttling is required.
2. Stem
The stem is the rod that connects the disc with the wheel. The solid stem must have very high tensile strength when the valve is opening and can withstand compression when closing. There are two types of stems.
Smooth Stems – We use this type in automatic globe valves in this wearable material covers the thread to prevent leakage and smooth operation. The material has to be replaced regularly to ensure the streamline flow of operation.
Threaded Stem – We use this type of stem in the manual globe. The stem is threaded so that we can rotate the wheel to open and close the valve.
3. Cage
The part of the valve surrounding the disc inside the valve body is called the cage. As the disc move, it opens the cage, which increases the flow. So, it means that the cage determines the flow of fluids within the valve.
4. Seat
The seats in the globe valves are either welded or screwed. The disc rest on seat to create a firm seal to prevent any leakage. Some globe also features a backseat that forms a seal between the stem and bonnet by avoiding the pressure from building against the valve’s packing.
5. Bonnet
Bonnets are a vital part of every valve. Bonnet provide a leakproof seal for the valve. We can attach the bonnet by screwing or welding it with the body. Bonnet gives extra strength, durability and pressure-tight seal to the valve’s body.
The Screwed bonnets are used in high-pressure pipes.
Working of globe valves
Globe valves are available in various sizes, configurations, material temperature and pressure rating but all of them work in the same manner. When we open the valve, the disc moves upwards perpendicular to the seat. The upward motion opens an opening that lets the fluid pass through. When we close the disc, it creates a tight seal with the seat and prevents leakage.
| Gate Valve. | Globe Valve. |
| We use gate valves for simple on/off controls. | Globe valves can also regulate the flow. |
| Gate valves offer significantly less resistance and negligible pressure drop when fully opened. | Globe valves offer high-pressure drop and high resistance when fully opened. |
| Gate valves are less expensive. | Globe valves are comparatively expensive. |
| Gate valve bind, if open against high differential pressure. | Globe valve easily opens against high differential pressure. |
| The gate moves parallel to the seat. | The gate/disc move perpendicular to seat. |
| We can use the gate valves in both directions as there are designs for both directions of flow. | The flow direction is indicated, and the flow of the fluids is according to it. |
| The gate valve has to be removed for repair. | You can repair the globe valve without removing it. |
| Gate valves are unidirectional. | Globe valves are multi-directional. |
Different Applications of Gate Valve and Globe Valve
Gate valve applications in industry
Gate Valves has a considerable number of applications. Some of the typical applications are as follows.
· Gate valves are used in large supply water systems because they have a linear flow and low resistance.
· They are found in old plumbing systems.
· They have applications with slurries and viscous mediums.
· They are also used in high temperature and high-pressure conditions such as in power plants and mining fields.
Globe valve applications
The globe valves have a large number of applications in almost all industries.
· Globes valves are used to regulate the flow in water cooling systems.
· We also use them in control circuits due to their ability to withstand different flow and pressure ranges.
· Their ability to stand high temperatures and pressure makes them perfect for high-pressure systems like steam engines and hydraulics.
· They are widely used in the automation industry as they are easy to install.
· They are ideal where leak safety is a significant concern.
Things to consider before buying Gate Valve or Globe Valve
Here are the things you must consider before choosing the gate or globe valve.
Use: Before buying you must know why are you using the valve. The use can be the regulation of fluid or stopping the fluids.
Type of Fluids: Both globes work differently with different kind of fluids. So, you must know what type of fluid will pass through the valve. Like it can be chemicals, medical fluids, edible fluids, or the liquid can be corrosive.
Operation of the valve: You must consider how you want to operate the valve, manually or automatically. OR you are going to operate the valve from a remote location.
Assembly: How are you going to assemble the valve, are you going to weld it or screw it with the pipes.
Pressure and Temperature: Pressure and temperature are two essential elements. High pressure can cause leakage or rupture in the valve and don’t buy an oversized valve. It is vital to know how much temperature can the valve withstand. The high temperature will damage the disc, which, as a result, effects the functionality of the valve.
Flow Rate: You must measure the flow rate of the fluid passing through the valve. High rate and the small valve will be disastrous and can cause valve breakage.