Gate valve v Knife gate valve: Which is better for your process?

In this article, PIF spoke to leading Scottish valve distributors, BM Engineering Supplies, to explore the similarities and differences between gate valves and knife gate valves. Although these shut-off valves are both used in on/off applications involving viscous fluids, there are some noteworthy design variances to consider when deciding which is best suited your process application. Here, we put the two head to head to see which valve type is better.

How does a gate valve work?

Gate valves open by lifting a round or rectangle-shaped gate out of the path of fluids. The sealing surface found between the gate and the seats is planar. As such, gate valves will often be used when a straight line of flow of fluids is required with minimum restriction. This popular shut-off valve type features a flat fate closure which slides either in and out, or up or down between two parallel plates to open and close the valve. With this in mind, gate valves are often used for shut-off operations as opposed to flow regulation operations as on or off are the only two settings available.

Applications of gate valves

• Oil & Gas
• Pharmaceuticals
• Automotive
• Power Plants
• Water Treatment
• Mining
• Offshore
• General Process Manufacturing.

Advantages and disadvantages of gate valves

One of the primary advantages afforded by using gate valves is that the pressure which drops can be very low when gate valves are fully open. While they are useful as on/off valves, they can also equally competent at performing bi-directional action. However, gate valves do require a large force to operate. Larger sized gate valves even require automatic actuators to operate. Gate valves are also not the quickest valve type to open or close. They also not the best suited for space-sensitive applications as they tend to take up more space compared to other valve types. In some cases, gate valves can also be prone to thermal expansion and shrinking when exposed to high-temperature fluctuations. As a result, this may provide applications with unwanted leakage.

How does a knife gate valve work?

Originally designed for the pulp and paper industry, knife gate valves perform exactly at their name implies. Stringy pulp would impinge between the wedge and sand seat of a normal gate valve to prevent flow shut-off. Knife gate valves feature a sharp edge to cut through the pulp and seal, a useful attribute which has seen this shut-off valve type become invaluable to applications which either deal with viscous fluids or ones which have a similar risk of impingement.

Applications of a knife gate valve

Sludge & Slurry
Paper & = Pulp
Wastewater
Heavy Oils

Advantages and disadvantages of knife gate valves

Knife gates are cheap, easy to actuate and light. They are advantageous in applications involving viscous fluids such as sludge and slurry because their blades can cut through thick liquids with ease. As such, they are generally specified in larger sizes for the handling of thicker flows in demanding applications. Despite this, knife gates are known for their low-pressure limitations. As such, this makes them a less desirable shut-off valve for applications which require cleanliness or optimal hygienic conditions.

Buy gate and knife gate valves from BM Engineering Supplies

As an established and trusted valve distributor to the Scottish process industry, BM Engineering Supplies stocks a comprehensive range of both gate valves and knife gate valves. For gate valves, BM Engineering is the Scottish partner for one of the UK’s market-leading valve wholesaler, Leengate Valves. Their range of gate valves is approved to ISO 9001 standards and other relevant industry governing bodies. While for knife gate valves, BM Engineering partners with Orbinox UK, one of the world’s leading manufacturers of knife gate valves.

For more information about BM Engineering Supplies range of gate valves and knife gate valves, visit their website.