What is a knife gate valve?
Knife gate valves are designed mainly for on-off and isolation services in systems with high content of suspended solids. Knife gate valves are especially beneficial for handling slurry in addition to viscous, corrosive and abrasive media. The valves have a minimised pressure drop in fully open position, they are easy to actuate, they have a relatively low weight and are cost-effective.
Where are knife gate valves used?
Knife gate valves are designed to work in some of the harshest 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.
What is the difference between knife gate valves and 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 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 a gate valve. These are the main differences and probably two of the biggest advantages of the knife gate valve.
Knife gate valves 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.
