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Simply a better way to remove reject

Privet’s Double Dumper® is a state-of-the-art solution for the intermittent removal of sand, stones, metal particles, and other material from pulp. Designed to replace conventional junk traps, the Double Dumper is easy to install and operate, and very cost-effective and safe.

Capable of replacing much more complicated conventional junk trap set-ups, while removing impurities just as efficiently, Privet’s patented Double Dumper® is based on a deceptively simple design.

Unlike a conventional junk trap, which normally consists of two main valves, two air evacuation valves, and a junk chamber, the Double Dumper looks more like a ball valve. Unlike a ball valve, however, the Double Dumper has a ‘wall’ through the middle of the ball opening that prevents material flowing through the valve.

Reject falls into the unit’s upper cylindrical chamber under gravity, and when sufficient reject has collected, the ball is turned through 180 degrees. This causes the contents of the upper chamber to be fed downwards, while the empty lower chamber is turned upwards to collect new reject.

All this makes the Double Dumper much simpler and easier to install and operate.

Simple to control

As a Double Dumper is normally operated with a pneumatic 180-degree actuator, and is equipped with a solenoid valve and double limit switches, it requires only three I/Os. This compares to 12 I/Os for a conventional junk trap, which requires one pneumatic line and three electrical cables – one for the solenoid and two for the limit switches – for each of its four valves.

Conventional junk traps also require the installation of special software on process control computers to operate the valves in the correct sequence. Safety systems are also needed to prevent the two main valves from being opened simultaneously, which would allow hot pulp to flow through at process pressure, with very serious potential consequences.

No special software is needed with the Double Dumper, in contrast, as it requires only a timing signal from the process control unit. Since it operates as a feeder, pulp cannot flow through under pressure, resulting in significantly better safety.

The Privet Double Dumper® is available in sizes ranging from DN50 to DN300 (2”-12”).

Compact design

The Double Dumper is also very compact. A conventional DN150 (6”) junk trap fitted with knife gate valves is approximately one metre high, for example, while an equivalent Double Dumper is only 350 mm high, and is also lighter.

Specifically designed for use in the pulp and paper industry, the Double Dumper has been widely used in conjunction with high-density cleaners and pressure screens, and it boasts a large number of OEM and mill references. The Double Dumper can also be used in other applications where reject is passed intermittently from a high-pressure system to a low-pressure one, and for sampling and dosing.

> Juhani Polón
(Published in High Technology Finland )