KNIFE VALVES

Knife gate valves work exactly as their name suggests. Such valves were originally designed for the pulp and paper industry. The fibrous pulp will collide between the wedge and seat of a normal gate valve and prevent flow interruption. Knife gate valves are designed to have a sharp edge to cut through pulp and sealant. With such useful features, the blade gate valve has become invaluable in applications involving slurry, viscous liquids, Particulate Liquids and other systems where collision is a problem.

Knife valves are advantageous in sludge and mud applications because the closing element Bicak easily cuts off viscous liquids. These are some of the blade gate valve applications, usually for the treatment of viscous flow heavy oils, light grease, slurry, pulp, varnish and waste water.

Advantages and Disadvantages

The advantages of blade valves are that they are inexpensive, easy to operate, and light. One of the most important disadvantages of blade valves is that they are known to have low pressure limitations. This makes them less desirable for use in applications requiring cleaning or sanitary conditions.

Types :

Wafer (Between Flange)

Lug

Double Flanged  Knife gate valves are designed to work in some of the most harsh environments, typically having a sharpened blade to cut through heavy liquids.

They are especially useful in wastewater applications where corrosion is an important issue. So, in addition to the valve design optimised for slurry media, it is beneficial to have a knife made of acid-proof stainless steel as this makes it less susceptible to damages caused by corrosion and as a consequence it needs less frequent maintenance or even replacement.

Knife gate valves should only be used for applications requiring a completely open or completely closed position and should not be used to regulate flow unless they are designed for it. Whenever fluid is forced against a partially closed gate, there will be a vibration, gradually eroding the disc and seat. In addition, the knife gate valves are designed to slowly open and close to safeguard against the impacts of water hammer.

Knife Gate Valves vs. Gate Valves

Both the wedge type gate valves and the knife gate valves are primarily designed for on-off services where the valve is completely opened or completely closed. It is not recommended to use neither of these to regulate flow because when fluid pushes against a partially closed gate vibration occurs, and cavitation will eventually damage the seat and the body. Also, both of the valve types are designed to open and close slowly in order to reduce the risk of water hammer.

Both types can be used in applications involving:

• Slurries
• Heavy oils
• Non-flammable viscous fluids
• Wastewater
• Clean water

One of the differences between the gate and the knife gate valves, is that the knife gate valve often has a sharpened disc to better cut through slurry/viscous media. Also, the knife gate valve has a short face-to-face length compared to a gate valve, which is dimensionally wider. As a consequence a knife gate valve is light weighted compared to the gate valve. These are the main differences and probably two of the biggest advantages of the 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.