KNIFE VALVES

Knife gate valves work exactly as their name suggests. This type of valve was originally designed for the pulp and paper industry. The fibrous pulp would hit between the wedge and seat of a normal gate valve and prevent the flow from being interrupted. Knife gate valves are designed to have a sharp edge to cut through the pulp and seal. With such useful features, the knife gate valve has become invaluable in applications involving slurries, viscous liquids, particulate liquids and other systems where slamming is a problem. Knife valves are advantageous in sludge and slurry applications because the closing element, the knife, easily cuts through viscous liquids. These are usually viscous flowing heavy oils, light grease, slurries, paper pulp, varnish and wastewater handling are some of the applications for knife gate valves.

Advantages and Disadvantages

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

Tipler :

Wafer (Between Flange) Lug Double Flanged (Double Flanged)

Knife gate valves are mainly designed for on-off and isolation services in systems with high solids content. Knife gate valves are particularly useful for conveying slurries, viscous, abrasive and corrosive media. The valves have a minimized pressure drop in the fully open position, are easy to operate, have a relatively low weight and are cost effective. Knife gate valves are designed to operate in some of the harshest environments, typically with a sharpened blade to cut through viscous liquids. They are particularly useful in wastewater applications where corrosion is a major issue. Therefore, in addition to the valve design optimized for slurry media, it is beneficial to have a blade made of acid-resistant stainless steel, making it less susceptible to damage caused by corrosion and consequently requiring less frequent maintenance or even replacement. Knife gate valves should only be used for applications that require a fully open or fully closed position and should not be used to regulate flow unless they are designed for this. When fluid is forced through a partially closed gate, there will be a vibration that gradually wears the disk and seat. Furthermore, knife gate valves are designed to open and close slowly to protect against the effects of water hammer.

Gate Valves with Knife Gate Valves

Both wedge-type gate valves and knife gate valves are primarily designed for on-off services where the valve is either fully open or fully closed. It is not advisable to use either of these to regulate flow because cavitation occurs when fluid pushes against a partially closed gate vibration and cavitation will eventually damage the seat and stem. Also, both types of valves are designed to open and close slowly to reduce the risk of water hammer. Available with Manual, Pneumatic and Electric Actuator, Both types can be used in applications including

• Slurries
• Heavy oils
• Non-flammable viscous liquids
• Waste water
• Clean water

One of the differences between gate and knife gate valves is that the knife gate valve usually 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 result, a knife gate valve is lightweight compared to a gate valve. These are the main differences and probably the two biggest advantages of the knife gate valve. Knife valve installations are typically found in wastewater treatment plants, chemical plants, mining, cement plants and many other industrial applications, while gate valves are typically found in drinking water networks, distribution networks and drinking water pumping stations.