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How Knife Gate Valves work

How Knife Gate Valves work

Issue Time:2022/06/18

Knife Gate Valves are commonly used in liquid, slurry and powder applications that include pulp and paper, bulk handling, mining, food, beverage, chemical and wastewater treatment designed for mainly on-off and isolation.

Knife Gate Valve cross section

Knife gate valves use a blade with a sharp or bevelled edge to cut through heavy liquid to stop the flow. The design of the knife gate allows the metal blade to glide through slurry and thick liquids quickly and easily making them invaluable when it comes to applications that involve viscous fluids, slurry and other systems where impingement is an issue.

Today knife gate valves can be found everywhere, in processing, biofuel and industrial plants. They are available with various operators, supplied in different materials and sizes.

Knife gate valves are compact making them easy to install with replaceable seats and seals allowing for straightforward maintenance.

Application

Knife Gate Valves shouldn't be used to regulate flow, whenever fluid is forced against a partially closed gate, it will gradually erode the disk and seat, resulting in constant maintenance or in the valve having to be replaced completely. Consequently, knife gate valves should only be used to either completely close off the flow or open to allow flow. In addition, these valves are designed to slowly open and close to safeguard against the impacts of water hammer (to read more about Water Hammer see our blog here >>).

These Valves are also restricted to low pressures and not recommended with gases or powder. When dry solid powder passes through a knife gate valve, it tends to pack into the soft seals around the gate and the seat over a time will wear, eventually, the gate will not close and start to leak dry dust. In this situation, you will need to replace the knife gate’s seal once it begins to leak and depending on where the valve is fitted it may be necessary to remove the entire valve out of the pipeline which in some cases can be difficult because of the size of the valve.

Types of Knife Gate Valves

At Valves Online we supply knife gate valves that are designed for arduous duty, in a range of materials and designs, including Uni-directional or Bi-directional where the design of the body and seat will ensure non-clogging to deliver tight shut off on suspended solid and liquid media.

Want to know the difference between a Uni-directional & Bi-directional Knife gate valve? Check our blog here >>

Manual

Manual Knife Gate valves have a handwheel which once turned makes the stem go up or down allowing the gate/ metal blade to be raised and lowered. Turning the handwheel clockwise will drop the gate and the valve closes. Turning the handwheel counterclockwise will raise the gate and the valve opens.

Available in Cast Iron, Stainless Steel and Ductile Iron, in various sizes and designs with a number of flange accommodations.

Manual knife gate valves

manual Knife gate valve diagram

Actuated

Using the same priceable as the manual knife gate, only the handwheel is replaced with a powerful Pneumatic/electric actuator

pneumatically actuated for process and general industrial applications including mining, water treatment, slurry, biomass and electric generation plant. Offered in both uni and Bi-Directional format, suitable to fit between various flange interfaces and a multitude of different materials and seals.

Actuated Knife Gate Valves

Actuated Knife Gate Valve Diagram

Knife Gate Valves Vs Gate Valves

Both gate valves and knife gate valves are designed for on-off duties with the valves completely open or close and not suitable for regulating flow. Both Valve types open and close slowly helping reduce the risk of water hammer. You can also use both designs for Slurries, Heavy Oils, Waist water and clean water.

One of the notable differences between the gate valve and the knife gate valve is that the knife gate valve often has a sharpened disc to help cut through slurry/viscous media. Also, the knife gate valve has a short face-to-face length making it more compact in comparison to the gate valve, which is dimensionally wider. This makes the knife gate valve much lighter in weight as well as streamline making them a more desirable choice for many applications.

Gate Valve vs Knife Gate Valve

Knife gate valve installations are typically found in wastewater treatment plants, chemical plants, mining, cement plants as well as in many other industrial applications while gate valves are typically found in drinking water mains, distribution networks and drinking water pump stations.

Knife Gate Valves from Valves Online

Valves Online have recently improved on our range of Knife Gate Valves. Adding to our already extensive collection of manual and pneumatic/electric actuated Knife Gate’s, with designs for arduous duty, in a range of materials from top manufacturers such as Bray/ VAAS and Zubi, at the best prices with quick delivery.

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