Table of content
A gate valve is a type of valve, appearing relatively simple in design. However, improper operation can still cause damage, such as damage to the valve seat or stem, or leakage. Gate valves come in various operating handles, including handwheels, electric, and pneumatic.
The main function of a gate valve is to control the gate by turning the handle, thereby controlling its opening and closing. This article will provide a more detailed introduction to gate valves, including but not limited to their working principle.
What is the Working Principle of a Gate Valve?
A gate valve is a type of isolation valve, and it is a multi-turn valve. Turning the handle or other means controls the gate or wedge, causing it to move up and down, thus controlling its opening and closing and the flow rate.
A gate valve has a linear flow path, unlike the internal rotation of a ball valve.
When the user turns the handwheel or starts the gearbox, the connected threaded rod will move synchronously, changing the rotational motion into linear motion. This controls the up and down movement of the gate, thereby controlling its opening and closing.
What Happens When a Gate Valve Opens?
When the handwheel is turned or the gearbox is started, the connected valve stem converts the rotary motion into linear motion, causing the gate to rise or fall, thus controlling the opening and closing.
The following are the steps to open a gate valve:
- Operator turns the handwheel
- Valve stem begins to rotate
- Gate begins to move
- Gate separates from valve seat
- The valve port is slowly opened, allowing fluid to pass through
- Gate fully open
When the gate is fully open, the internal orifice of the gate valve matches the pipe diameter, allowing for smoother transmission.
The number of turns required to fully open the gate depends on factors such as the valve stem pitch, valve size, gate travel, and other parameters.
Turn the handwheel until it is fully open, i.e., until it cannot be turned any further. Do not continue turning, otherwise it may cause breakage.
What Happens When a Gate Valve Closes?
To close, simply turn the handwheel counterclockwise to lower the gate.
The specific operation corresponds to the following internal motion:
- Turn the handle
- This rotates the valve stem
- The gate moves downwards in a straight line
- Completely closes the gate.
Whether it is completely closed depends on the following factors:
- Whether the valve stem rotates correctly
- Whether the gate is aligned
- Whether the valve seat torque is sufficient
- Whether the sealing surface is clean
- Whether the tolerance is within range
- Whether the raw materials are suitable
If the gate is not completely closed, leakage may occur. However, if too much force is used when closing the handwheel, it can also cause deformation of the sealing surface, resulting in leakage.
How Does the Stem Move the Gate?
The gate valve is opened and closed by turning the handwheel, which moves the valve stem, causing the gate to move up and down. Opening the valve upwards opens it, and closing it downwards closes it.
The following is the corresponding opening and closing mechanism for the gate valve:
| Stem Design | Operating Movement |
|---|---|
| Rising stem | The stem rises visibly as the valve opens |
| Non-rising stem | The external stem height remains nearly constant while the gate moves internally |
The rising stem in the gate valve has a very clear visual effect. When the stem is extended, the gate valve is open.
In some compact environments, the rising stem is generally not used. However, the valve position still requires an independent indicator.
How Does the Gate or Wedge Stop the Flow?
The gate, also called a wedge, is used in this gate valve to move the valve.
The gate descends between the gate and seat, contacting the sealing surface to close the pipeline.
Wedges can be solid or flexible, but regardless of their shape, they are used for sealing.
The following are points to note during production:
- Gate thickness and shape
- Guide rail dimensions
- Sufficient flatness of the sealing surface
- Surface cleanliness
- Dimensional stability
For products with high requirements or corrosion resistance, the sealing surface needs to be made of corrosion-resistant alloy steel.
How Do the Gate and Seats Create Shutoff?
The valve seat is a fixed component installed in the valve body and is used to seal with the gate.
Gate valve seats are usually also made of metal; the choice between stainless steel or carbon steel depends on quality and sealing requirements.
| Sealing Factor | Effect on Valve Operation |
|---|---|
| Seat alignment | Determines whether the gate contacts both seats evenly |
| Surface finish | Influences leakage rate and sealing stability |
| Hardfacing | Improves wear, erosion, and galling resistance |
| Differential pressure | Affects seating load and required operating torque |
| Debris | May scratch surfaces or prevent complete closure |
| Thermal expansion | Can change clearances and contact pressure |
The seal between the gate and seat is achieved by the pressure difference across the valve pushing it in; this pressure maintains its torque. Therefore, the actuator torque must take into account the torque under maximum pressure difference.
What are the Fully Open, Partially Open, and Fully Closed Positions?
These are the three states of a gate valve.
Fully Open
The gate is fully raised to its maximum height, opening its passage completely. This is the fully open state, with no resistance.
Partially Open
The gate is raised to a partial height, the specific height depending on the desired flow rate. In this state, some resistance, turbulence, and vibration will occur. Prolonged exposure to this state can affect the guide rails and sealing surfaces.
Fully Closed
The gate is completely at its lowest point, which is the closed state. Do not operate too forcefully when closing, as this will affect the seal.
Why Is a Gate Valve Not Recommended for Throttling?
Gate valves are designed for isolation, not flow regulation. Prolonged exposure to a regulating state can compromise the seal.
Besides affecting sealing performance, gate valves also affect the following aspects:
- Gate valves will vibrate.
- Flow will be unstable.
- Noise will be generated.
- Cavitation may occur under certain conditions.
- Corrosiveness to sealing surfaces will occur.
- Affecting the tightness of closure.
Regardless of whether flow control valves are used for precise flow control, a suitable control valve must be selected if flow regulation is required.
How Do Pressure and Flow Direction Affect Operation?
Pipe pressure acts on the gate valve, stem, body, and seat. The pressure difference between upstream and downstream directly affects the stem thrust.
Under a high pressure difference, the gate valve will press against the downstream seat, increasing the initial opening force.
The size of the gate valve also affects its pressure difference and torque. Therefore, buyers should pay attention to the following when purchasing:
| Operating Parameter | Why It Matters |
|---|---|
| Design pressure | Determines pressure-boundary requirements |
| Maximum differential pressure | Affects opening torque and stem thrust |
| Operating temperature | Influences material strength and clearances |
| Flow direction | May affect seating behavior in some designs |
| Valve travel | Determines stem movement and actuator settings |
| Operating frequency | Influences wear and actuator selection |
Some gate valves have a bidirectional closing function; this needs to be confirmed with the manufacturer before purchase.
How to Perform Packing, Bonnet, and Body Support Operation?
Some components of a gate valve do not affect its flow rate but do affect its sealing performance, such as the valve body, bonnet, packing, gasket, and bolts.
The valve body needs to withstand pipeline pressure and provide internal flow channels.
The packing surrounds the valve stem inside the packing box to prevent leakage.
The bonnet compresses the packing under pressure; too loose will cause leakage, while too tight will increase friction and torque.
Does Material Change How a Gate Valve Work?
No. Whether made of carbon steel or stainless steel, gate valves operate on the same principle.
The only differences are in performance, pressure resistance, and corrosion resistance.
Carbon steel is mostly used in general industrial systems, with ASTM A216 WCB being the most common. Stainless steel is mostly used in products requiring corrosion resistance, with ASTM A351 CF8 and CF8M being the most common grades.
How Is a Gate Valve Operated Manually or Automatically?
Gate valves can have many operating mechanisms.
| Operating Device | Operating Principle |
|---|---|
| Handwheel | Manual multi-turn input moves the stem mechanism |
| Gearbox | Reduction gearing lowers the required manual force |
| Electric actuator | An electric motor supplies torque for remote operation |
| Pneumatic or hydraulic actuator | Fluid pressure produces the required movement or thrust |
The above lists the various operating devices for gate valves. The selection of the actuator needs to consider seat torque, release torque, stem thrust, total stroke, operating speed, differential pressure, and safety factor.
What Should Industrial Buyers Check Before Ordering?
Whether you are a distributor or a construction company, you need to consider the following aspects before making a purchase:
| Buyer Check | Technical Requirement |
|---|---|
| Valve size | Match the DN or NPS pipeline size |
| Pressure class | Confirm PN or ASME Class rating |
| Body material | Specify the exact carbon steel or stainless steel grade |
| Gate and seats | Confirm materials, hardfacing, and sealing structure |
| Stem design | Confirm rising or non-rising construction |
| Operation | Select handwheel, gearbox, or actuator |
| Torque and thrust | Verify seating and unseating requirements |
| Valve travel | Confirm full open-to-close movement |
| Leakage requirement | Define the accepted seat-leakage criterion |
| Testing | Require shell, seat, and operational tests |
| Documentation | Review drawings, BOM, MTCs, and test reports |
As a renowned valve manufacturer in China, we guarantee that all our valves are manufactured strictly according to standards and customer requirements. Furthermore, our company provides third-party testing.
Summary
The above is a detailed introduction to gate valves. In short, a gate valve converts a rotating stem into a linear gate motion. The gate opens when raised and closes when lowered.
