Knife Gate Valves Resource Guide for Engineers

When selecting knife gate valves for tailings applications within a mining project, numerous critical factors must be carefully evaluated to ensure optimal performance and longevity. 

Our specialists consider the following parameters to specify the most suitable knife gate valves for your project: 

• Actuation Requirements 
• Corrosiveness 
• Frequency of operation 
• Media temperature 
• Particle size 
• Percentage of solids 
• Pumping pressure 
• Shutoff criteria 
• Slurry characteristics 
  
  

These parameters encompass a spectrum of factors ranging from mechanical specifications to the intricacies of the environment in which the valves will operate. Each parameter plays a pivotal role in safeguarding against potential issues and optimising the efficiency of the valve system within the challenging terrain of mining operations. 

The bonded urethane lining is a key feature that contributes to the longevity of a knife gate valve. The distinct advantage of a one-piece bonded liner is that there are no gaps behind the seat, as there is with a replaceable liner. The gap may be detrimental in processes where the body material can be attacked (corrosiveness). A bonded urethane liner protects the valve body from the abrasive and corrosive action of a slurry, which can significantly extend the service life of the valve. The urethane lining is cast in place, which ensures that it is securely bonded to the valve body and will not dislodge or wear away as quickly as other types of linings can be prone to.  

In comparison to other types of knife gate valves, such as those with replaceable seats or those without any lining, bonded urethane knife gate valves do offer a longer service life due to the protection the urethane lining provides against abrasive wear.  

The cast-in-place urethane lining requires less frequent repairs due to wear. However, if repairs are needed, the ability to replace components such as the gate or packing would be a consideration in the overall repairability of the valve. 

Bonded urethane knife gate valves, such as the DeZURIK KUL, are designed for on-off applications of abrasive slurry and dry abrasive materials. These valves are particularly well-suited for mining, chemical, and food industries due to their robust construction. The urethane lining in these valves provides bi-directional, drip-tight shutoff to the full valve rating, and all wetted surfaces of the ductile iron body are lined with urethane, which can be beneficial for longevity in service. Additionally, the design of the KUL valves has a 100% port area, which is ideal for applications involving abrasive materials as there are no restrictions or cavities where particles can accumulate and cause wear or blockage. 

In summary, bonded urethane knife gate valves are designed for durability and longevity in abrasive applications, with the urethane lining providing significant protection against wear. This can lead to a longer service life and potentially less frequent repairs compared to other types of knife gate valves. 

Understand the Slurry Properties: Knowing the properties of the slurry, such as its abrasiveness, corrosivity, and solid content, is crucial for selecting the right type of valve and materials for construction (see FAQ 1 for further information). 

Choose the Right Type of Valve: Select a valve type with a 100% port area to ASME B36.10 which provides a high flow capacity with minimal pressure drop. This greatly reduces erosion caused by high velocities and turbulence which reduced or non-round port valves create. For high pressure applications, look for valves that conform to ASME B16.34. For lower pressures, look to MSS-SP81 and MSS SP-151 specifications. Referencing these standards ensures design integrity. 

Select Appropriate Construction Materials: The materials used for the valve body, gate, and other components should be chosen based on the slurry's corrosive and abrasive nature. Special coatings or treatments on the gate can also be considered such as Nedox. 

Consider Pressure and Temperature Ratings: Ensure that the valve can withstand the pumping pressure and temperature requirements.   

Ensure Positive Shut-Off Qualities: The valve should have positive shut-off qualities to prevent leakage, which is critical for maintaining system integrity and environmental safety. 

Full-Force Lockout System: The valves should be able to be locked out for downstream maintenance. Designed for safety, the lockout system should be able to hold the full actuator force plus a safety factor. 

Exercising: Regularly opening and closing of the valve according to the frequency of operation can increase the lifespan. Particularly for applications where dewatering and/or scale build-up occurs. 

Regular Maintenance and Inspection: Adjust the packing regularly, lubricate the stem and stem nut, and ensure regular exercising. This helps to extend the life of the valve and ensures reliable operation. 

Evaluate Underperforming Valves: If existing valves are failing frequently, consider replacing them with newer designs that offer improved shutoff and longer service life. 

Consult with Valve Specialists: Work with a suitable supplier who can provide recommendations based on the specific requirements of the application and the characteristics of the slurry. Their knowledge and experiences are invaluable. 

By carefully considering these factors and strategies, you can select knife gate valves that are well-suited for the harsh conditions of mining slurry processes, thereby reducing the likelihood of valve failure and associated costs. 

In the lithium mining process, the type of knife gate valves that demonstrate optimal performance are severe service knife gate valves. These valves are recommended over rubber-seated knife gate valves due to the hard, sharp nature of lithium slurry, which can cause damage to softer materials. They are designed to withstand the abrasive and corrosive nature of the slurry encountered in lithium mining. 

The challenges presented by the lithium mining industry include handling hard, sharp slurry that can build up between the gate and rubber seats, causing damage and leading to increased maintenance and/or replacement costs. Additionally, high-velocity slurry can rapidly wear through valve components, such as diaphragms and bodies, including downstream pipework. To address these challenges, severe service knife gate valves encompass features such as full port or match pipe ID, hardened seat rings with hard facing overlay options, robust and field-adjustable packing systems including upper and lower scrapers to extend operating life and prevent loss of the media to the environment. 

These valves are designed to provide improved shutoff and a much longer service life while allowing zero product leakage to the environment, which is crucial in applications where the tailings are hazardous. 

For dewatering processes in mining, especially when dealing with slurry, the recommended knife gate valves are those designed for severe service conditions. These valves are engineered to handle high-pressure, highly abrasive slurries that result from intense water recovery and reclamation efforts in mining operations. The slurry, once dewatered, becomes more erosive, which necessitates the use of valves that can withstand such harsh conditions. 

Severe service knife gate valves are suitable for these applications as they are designed to provide improved shutoff and a much longer service life while preventing product leakage to the environment. Typically, these valves meet ASME 150# and 300# class ratings, allowing them to handle pressures up to 750 psi at ambient temperatures. They feature enhancements such as multiple scrapers and packing seals, which contribute to their longevity and zero leakage performance. The expected service life of knife gate valves in mining applications can vary widely depending on the severity of the service. For highly abrasive slurry handling, such as ore and tailings, the typical life can range from 12 to 36 months. 

The DeZURIK KSV is an excellent choice for high pressure, high abrasive slurry applications, whereas the DeZURIK KUL is a great option for lower pressure installations.