Q&A from DFT’s Webinar: Check Valve Solutions for the Mining Industry
Following our webinar, Check Valve Solutions for the Mining Industry, we’re sharing some of the questions from the audience along with our detailed answers. In the webinar, presented by Arie Bregman—who brings nearly five decades of experience in the valve industry—we explored the role of check valves in dewatering, slurry transport, and preventing backflow. We covered best practices for sizing check valves correctly to ensure optimal performance in mining applications, strategies to prevent water hammer and mitigate pressure surges with non-slam check valves, and how proper valve selection can reduce maintenance while improving operational efficiency. Arie’s technical expertise and commitment to industry education make him the ideal guide for these critical topics. If you missed the webinar, you can now watch it on demand on the DFT® website—just [click here].
Q: Wont Gravity help close a swing check valve in a vertical flow up application?
A: Gravity will absolutely close a swing check valve, after the flow has already stopped. This will cause water hammer to occur every time. The Axial Flow design incorporates an internal spring that opposes the flow and will start closing the valve as the flow rate starts to drop due to pump shut down. If the valve has a cracking pressure of 0.39 psi (as I used in our sizing example), then when the flow rate results in a differential pressure through the valve of less that 0.39 psi the valve will be closed. Because flow hasn’t reversed you will avoid the hydraulic shock and resulting shock waves with the fluid inside the pipe.
Q: In a low flow application can you remove the spring in an axial flow check valve?
A: Yes you can remove the spring in an axial flow valve, but doing so will negate the benefit of water hammer reduction/elimination. You will also limit the installation orientation options when the spring is removed. The valve will continue to work because the reversing flow will now close the valve. This means that the valve will continue to function with a missing or broken spring, you just have to understand that the advantage of water hammer reduction/elimination of the axial flow design is now lost.
Q: How low of a cracking pressure spring can you specify?
A: Cracking pressure lower limits are a function of the size of the valve. Smaller valves have very light weight discs and so small screwed end valves from ½” up to 2” can tolerate a 0.1 psi spring while over coming any internal friction factors and still closing the disc against the seat. There are many steam condensate applications that need such a low cracking pressure, and those valves work very well in that environment. From about the 3” line size up to about an 8” line size the lower end of cracking pressures is about 0.25 psi. In all cases the factory should be consulted regarding lighter spring selection options. There is no one size fits all rule here, internal friction, disc/stem weight all play a role in determining the lower end of check valve cracking pressure.
Q: How does vertical flow down effect valve selection?
A: Vertical flow down is another unique application orientation that requires factory consultation. The weight of the disc/stem subassembly coupled with the spring selection all play a role coupled with any desired static fluid head that may need to be retained above the valve. The factory team understands these issues very well and are on hand to work with you to help you select the right valve for these applications.
Q: Is axial flow check valve suitable for slurry application
A: Yes, Axial Flow check valves can be used in slurry applications. The main concern with slurries would be the maximum particle size that would be contained within the slurry. Maximum particle size is always dependent on the nominal valve size and the amount of opening between the disc and seat that is available for the particles to pass through. Generally speaking, the amount of lift in an axial flow check valve is about 1/4 of the NPS, so a 4″ valve might have about 1″ of lift. The maximum particle size would be about 1/2 of that to allow it to pass easily through the valve.
Q: Are there any applications or process conditions where axial flow check valves are prone to damage, such as slugging?
A: High concentrations (above 25%) of large particles whose size exceeds 10% of the valve Nominal Pipe Size could be problematic for axial flow valve designs because of the potential for these particles to cause clogging of the valve. Lower concentrations of approximately 10% in a aqueous slurry should be able to flow through the valve with no major issues.
Q: In the case of higher solids content (20-30% by weight) do these valves perform well? The spring is not affected by the solid particles?
A: 20-30% solids whose maximum size is less than 5% of the valve NPS should not cause major problems. In all cases the spring is on the down stream side of the disc and is protected from direct impingement by solids in the media flowing through the valve. I wold urge you to discuss these applications with the factory to get their guidance early on in the specification process. All applications have unique parameters, and it is always difficult to give a one size fits all answer when it comes to solids in the flow stream.
Q: Would two valves back-to-back work? sometimes the process specifies two of them for safety
A: 2 valves back-to-back should work just fine. I would recommend that the 2 valves be spaced apart by at least 5 times the NPS to allow for the flow to restore to a more laminar flow as it enters the second valve. Excessively turbulent flow will cause unbalanced forces to act on the internal trim components of the second valve potentially leading to vibration related damages to occur.
Q: What’s the most challenging aspect of manufacturing these valves? How do you manage performance variability caused by assembly variation?
A: Axial flow check valves are relatively simple designs that are not too overly complex to manufacture. The manufacturing tolerances that impact the amount of opening of the valve and the space provided for the spring may have a very minor impact on the flow capacity (Cv) of the valve as well as a small impact on the cracking pressure of the valve. Generally, the Cv variability will be less than 1% of the stated value while the cracking pressure could vary by +/- 5% of the nominal published value.
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