When are knife gate valves used?

What is a knife gate valve?

Knife gate valves are designed primarily for on/off and isolation service in systems with high suspended solids content. Knife gate valves are particularly suitable for handling slurry, viscous, corrosive and abrasive media. These valves have minimal pressure drop in the fully open position, they are easy to start, they have a relatively low weight and are cost effective.

When are knife gate valves used?

Knife gate valves are commonly used in mining, power plants and in the paper, chemical and food industries. Knife gate valves have the advantage of being very compact due to the linear movement of the closing flap (the plate that stops the flow of fluid in the closed position). The knife gate valve is primarily a globe valve, although it can also be used as a control valve when the flapper valve is in the partially open position.

Knife gate valves can be used for fluids containing solid particles, such as waste water or sludge. Generally, knife gate valves are designed to seal on the upstream side of the circuit (fluid inlet side), but some valves are sealed on both sides so that a knife gate valve can be used regardless of the direction of fluid flow. In the open position, the pressure head loss is very low because the valve does not cause a change in fluid direction.

However, closing and opening times can be long and periodic maintenance is also required to correct wear problems between the flapper valve and the seals.

Important features

Low space requirements in terms of thickness

Low pressure head loss

Compatible with fluids containing particles

What is the difference between a knife gate valve and a gate valve?

Wedge gate and knife gate valves are primarily designed for on/off service where the valve is fully open or fully closed. Both are not recommended for regulating flow because cavitation can eventually damage the valve seat and body as the fluid pushes the partially closed gate to vibrate. In addition, both valve types are designed to open and close slowly to reduce the risk of water hammer. 

Both types can be used in applications involving 

▸Clean water

▸Slurry

▸Wastewater

▸Heavy oils

▸Non-flammable viscous fluids

One of the differences between gate and knife gate valves is that knife gate valves typically have a sharp disc to better cut through slurry/viscous media. In addition, knife gate valves have a shorter face length compared to the wider sized gate valves. As a result, knife gate valves are lighter in weight compared to gate valves. These are the main differences and possibly the two biggest advantages of knife gate valves.

Knife gate valves are typically used in wastewater treatment plants, chemical plants, mining, cement plants and many other industrial applications, while gate valves are typically used in potable water mains, distribution networks and potable water pumping stations.