Factors That Make You Decide to Choose a Knife Gate Valve
One of the biggest advantages that make you choose a Knife Gate Valve is the weight and cost. Typically, the weight of a 16-inch knife gate valve is less than 300 pounds, while the weight of various types of ANSI gate valves exceeds pounds or more. The cost of the valve is also comparable to the weight difference.
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The knife gate valve was originally designed for the pulp and paper industry. When pulp accumulates between the knife and the seating surface to prevent flow stoppage, the knife gate valve is used to handle it. It features a sharp edge to cut through the pulp and seal to handle viscous fluids with similar clogging risks.
This type of valve is typically used in the heavy oil industry, wastewater treatment, pulp and paper industry, slurry, and sludge. These devices are usually specified in larger sizes to handle viscous flows in several demanding applications.
Factors That Make You Decide to Choose a Knife Gate Valve
One of the differences between other types of gate valves and the knife gate valve is that the knife gate valve usually has a sharpened disc to better cut through slurry or viscous fluids. Also, the knife gate valve has a short face-to-face length compared to the gate valve, where the latter is larger in dimensions. As a result, the knife gate valve is lighter in weight compared to the gate valve. These are the main differences.
Knife gate valves are commonly found in wastewater treatment plants, chemical plants, mining operations, cement plants, as well as many other industrial applications, while gate valves are typically found in main water networks, distribution networks, and potable water pumping stations.
Advantages and Disadvantages of Using a Knife Gate Valve Compared to Other Types of Gate Valves
Advantages of Using a Knife Gate Valve
Efficiency in Handling Viscous Materials:
The knife gate valve is designed to handle viscous materials and fluids that contain solid particles such as slurry and sludge. The knife blade cuts through the materials easily, preventing clogging.
Compact Design:
The knife gate valve typically has a compact design and short face-to-face length, making it easier to install in tight spaces.
Low Cost:
Compared to other types of gate valves, the knife gate valve is less expensive in manufacturing, installation, and maintenance.
Ease of Maintenance:
Maintenance and repair are generally easier and less costly due to the simple design of the knife gate valve.
Better Flow Control:
The knife gate valve provides better flow control when dealing with dense fluids compared to traditional gate valves.
Disadvantages of Choose a Knife Gate Valve
Low-Pressure Limitations:
The knife gate valve is not suitable for high-pressure applications, as it may not provide adequate sealing for such pressures.
Inefficiency in Hygienic Applications:
It is not the best choice for applications requiring high sanitary conditions such as food and pharmaceutical industries, due to the difficulty in thoroughly cleaning it.
Blade Erosion:
The knife blade may erode over time, especially when used with solid or abrasive materials, requiring regular replacement.
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Poor Performance with Dry Particles:
The performance of the knife gate valve declines when used with dry particles or granular materials, as the seal may not be tight enough.
Periodic Inspection Requirements:
It needs regular inspections to ensure no leaks and to confirm the cutting and sealing efficiency, which increases long-term maintenance costs.
General Comparison Between Knife Gate Valve and Other Gate Valves
Traditional Gate Valves:
- Suitable for high-pressure applications.
- Provide good sealing for applications requiring hygienic conditions.
- More expensive and heavier than knife gate valves.
- Less efficient in handling viscous materials and solid particles.
Ball Valves:
- Provide tight shut-off and easy operation.
- Can be used in both high and low-pressure applications.
- Not suitable for handling solid or viscous materials.
- More complex and expensive than knife gate valves.
Butterfly Valves:
- Lightweight and easy to install.
- Effective for large flows and low pressures.
- Not ideal for handling viscous fluids or solid particles.
- Less costly than knife gate valves but less durable.
By considering these advantages and disadvantages, the most suitable type of valve can be selected according to the specific application requirements and operating conditions.
As one of the resident bloggers here at Crane, I get ideas for blog posts all the time. The other day, an idea for a post about the difference between a gate valve and a knife gate valve came across my desk. “Seriously?” I said. “Isn’t the only difference that the knife gate has a sharper disk?”
I should have known the difference was not so cut and dry, pardon the pun. While the gate valve and knife gate have many similarities, there are characteristics to these valves that make them inherently different.
What makes them similar?
Gate and knife gate valves are primarily for on/off service. Using these types of valves to regulate flow is not recommended because when fluid pushes against a partially closed gate vibration occurs, eventually wearing and eroding the seat and disk. For that reason, these types of valves should be either completely opened, or completely closed.
These valves are also designed to open and close slowly to protect from the effects of water hammer.
Both types of valves can be found in applications that involve:
- Slurries
- Heavy oils
- Non-flammable viscous fluids
- Wastewater
- Clean water
What makes them different?
The differences between them are vast. First off, yes, the knife gate valve DOES have a sharpened disk (thank you very much). This is meant to sever any stringent solids that may keep the valve from closing and causing it to leak. But there’s more that makes their designs quite different.
The biggest difference between these two types of valves is that gate valves are built to ANSI standards while knife gate valves adhere to TAPPI standards. Therefore, dimensionally the gate valve is wider, flanged, and ANSI pressure rated. It also has API leak tightness standards must be met. They're bi-directional, and commonly used in steam applications as well as fluid applications. The gate valve is only available with metal seats.
Another significant difference between an ANSI gate valve and a knife gate valve is in the packing gland area. A gate valve will have a v-ring packing set that seals the shaft attached to the gate, while a knife gate valve has a packing gland that seals around the gate.
A knife gate has a very thin profile compared to its bulkier counterpart. It's also uni-directional (though bi-directional is an option on some), and comes in either wafer or lugged body, no flanges. The seats on the knife gate valve come in everything from metal to resilient types.
Two of the knife gate's biggest advantages knife are weight and expense. A 16” knife gate valve will typically weigh less than 300# while an ANSI gate valve will be in excess of #. The cost of the valve is similar to the weight difference as well.