McLanahan | Separators™

How Separators™ Work

The Separator™ differs from a conventional Hydrocyclone in that a rubber underflow regulator, sometimes called a fishtail, is fitted to the apex and an overflow pipe of specific diameter and length is fitted to the overflow flange. The overflow pipe returns below the apex and creates a siphon that closes the regulator when the pipe is full. An air valve is fitted to the overflow pipe and air is bled in to regulate the amount of siphon generated. These units are common in aggregate and sand operations as this configuration allows consistent underflow density almost regardless of feed density. The originally patented technology was used globally to improve the application of Hydroyclones in many industries. This benefited any moisture sensitive downstream process, such as stockpiling and attritioning.

Why McLanahan Separators™

Many other approaches attempt to mimic the results but the McLanahan Separator™ is the original siphon-assisted or vacuum-assisted Hydrocyclone developed and patented more than 40 years ago. This development answered many issues that plagued Hydrocyclones, especially when used for stockpiling sand. This equipment is still a standard today for stockpiling and inter-stage processing where underflow density control is critical. McLanahan personnel have a high level of experience with Separators™ and the ability to integrate them into systems large and small.

McLanahan Separators™ have no moving parts and take up minimal flood space, yet they can process high volumes of material while remaining relatively inexpensive.

Scavenger Systems

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A Scavenger System consists of a Sump, Slurry Pump and Separator™. It recovers fine product-sized material from the overflow of a Fine Material Screw Washer and discharges it into the product pile where it belongs. The overflow from the sand screw enters a Sump, where it is then pumped up to a scavenger Separator™ installed over the discharge end of the screw. The Separator™ recovers the fine product-sized sand particles and discharges them onto the dry deck area of the screw to discharge with the final sand product. 


Separators™ are modified Hydrocyclones. Hydrocyclones are used for classification, desliming and densification. Applications for Hydrocyclones include fines recovery, classification in ball mill circuits and concentrating Hydrosizer™ feed.

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Frequently Asked Questions About Separators™

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There are several reasons why this might be happening. Air is the killer of Separator™ operation. First, check to see if there is much siphon at the siphon valve — check if it is open or closed. Air is probably getting into the system by one of the following means: through the Sump to the Pump with entrained air — turbulence or plunging slurry stream; or leaks in the suction-side piping. Is the siphon boot still attached and in good condition? There could also be leaks in the Separator™ overflow piping. Other possibilities include a foreign object in the apex, rubber loose in the bottom of the Separator™. Is the underflow regulator (fishtail) in good condition? Is the overflow pipe blocked by the bottom of the overflow collection box? Is the collection box filled with slurry such that the overflow pipe is not 6ft (2m) below the underflow regulator? Systematically eliminate causes from the beginning of the system and work your way through. Note every instance along the way in case you need to call for help.

Typical applications with 2.7 SG material would be below 23% solids by weight. There is a risk of choking the Separator™ and having unstable operation at higher concentrations.

Yes, this is actually why this technology was invented and patented by the people who trained our personnel — in other words, you bought the original. Separators™ are actually Hydrocyclones with the addition of an underflow regulator (sometimes called a fishtail), overflow pipe and siphon valve (see How it Works section). Hyrdocyclones have an uncontrolled discharge that fluctuates in density depending on the feed density. The underflow regulator is tuned by adjusting the siphon valve to operate over a wide range of feed densities — this prevents the stockpile from being washed away at low feed densities.

It is possible to automate the Separator™ at additional cost; this is useful if there is constant variation in feed solids that are not being tolerated by the manual system. This can be the case with dredge-fed systems.

Purists will tell you this. They will also say it leads to inefficiency. It is true that a Hydrocyclone has an air core up through the middle of the Hydrocyclone starting at the apex. In the case of a Separator™, the underflow regulator blocks off the air core; however, since its introduction in the 1960s, the Separator™ has worked satisfactorily in countless applications from simple aggregate dewatering to highly controlled mineral processing environments, providing the ability to adjust the underflow density for downstream moisture sensitive applications like Attrition Cells. The cut-point can also be adjusted such that in a desliming application, fine adjustment can reduce losses of useful minerals in the overflow while reducing the unwanted fines content of clays and ultra-fines in the underflow.

Separators™ are ideal for stockpiles and moisture control while maintaining efficiency.

Features & Benefits
  • Designed to accept variations in feed solids content
  • Provide consistent underflow densities
  • Allow adjustable underflow densities
  • Allow minor adjustments to separation points

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Our customer service team is here to help you 24/7. We can ship you parts, send field service technicians to your site and answer any questions you have. Whatever you need, we are here for you.