Knife Gate Valve VS Gate Valve

Mar. 21, 2022

knife gate valve

PZ Series Knife Gate Valve


What is a knife gate valve?

The opening and closing part of the knife gate valve is a gate, and the movement direction of the gate is perpendicular to the direction of the fluid. The knife gate valve can only be fully opened and fully closed, and cannot be adjusted or throttled. The completely open channel can prevent the deposition of the medium in the valve. The knife gate valve is mainly composed of the valve body, 0-ring, gate, valve stem, bracket, and other components. The knife gate valve adopts the integrated structure of the clamp, which is small in size and light in weight. The replaceable sealing structure is adopted to solve the difficult maintenance problem of the ordinary slurry valves and knife gate valves. The material of the valve body is changed from traditional cast steel to nodular cast iron, which has better corrosion resistance and effectively extends the service life.


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 1200#. The cost of the valve is similar to the weight difference as well.


The difference between knife gate valve and gate valve

  • The knife gate valve has a knife-shaped oblique cut at the bottom of the valve plate, which has the function of cutting off the medium so that the valve is closed without being blocked by the medium.

  • The function of the knife gate valve is that it can only be used as a cut-off function and cannot be used as a throttling.

  • The gate valve can be used for throttling or as a switch.

  • Compared with ordinary gate valves, knife gate valves are simple in structure, small in size, flexible in operation, easy to install, and suitable for medium with higher consistency and solid particles.

  • The full-bore knife gate valve design allows the valve to be used under dirty conditions, and the replaceable seat and packing make the valve easy to maintain.

  • Because of its better performance, the price of knife gate valves is generally higher than that of gate valves. 


Knife gate valve and gate valve use range

The knife gate valve has a good shearing effect due to the knife gate valve, which is suitable for viscous particles. It is most suitable for fluids that are difficult to control, such as slurry, powder, and fiber. It is widely used in papermaking, petrochemical, mining, drainage, food, and other industries. The knife gate valve has a variety of valve seats to choose from. And can be equipped with electric devices or pneumatic actuators according to on-site control requirements to realize automatic valve operation.

Gate valves are generally used in industries such as the chemical industry, metallurgy, power stations, mining, pharmaceuticals, boilers, tobacco, hotels, construction, and textiles, with a wider range of applications.

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Advantages of knife gate valve

1. The opening and closing of the knife gate valve are labor-saving. 

2. The fluid resistance is small, and the sealing surface is less brushed and corroded by the medium.

3. The gate valve has a simple shape, short structure length, good manufacturing skills, and a wide range of applications. 

4. The flow direction of the medium is not restricted, does not disturb the flow, and does not reduce the pressure.


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