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Rotary Valve/Delumper



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Rotating material halfway around a circle gives the rotary valve an advantage similar to the twin screw and Bulk Solids Pump approaches: that of capturing material in a confined space, moving it to another point, and discharging the load.

Rotary valves, also referred to as rotary airlock feeders, rely on gravity to receive and discharge material. Discharge is assisted by rotational speed as well, and may be augmented by compressed air as needed. As the valve rotates, the voids between its upwardly facing vanes fill with material. A little more rotation and the pocket becomes sealed. Still further rotation opens the pocket again and allows its contents to discharge. Since the rotary valve seals its com¬partments effectively airtight, it is especially appropriate for use where pressure differentials exist.

Rotary valves are used on a range of free-flowing to highly floodable materials, but they may find hard-to-flow materials difficult because of the feeder’s primary reliance on gravity discharge, which may not always be sufficient to empty the downwardly pointing pockets. In such a case the use of a blow-through rotary airlock may be required, where compressed air assists in discharging the material.

Due to its operating principle, when used as a feeding device (rather than simply as a valve), and where consistency of the discharge stream is a concern, the device should operate at a speed sufficiently high to avoid discharge pulsing, yet not so high that its pockets do not fill consistently.

When applied as a gravimetric feeder, the rotary airlock feeder requires the addition of a weighing capability such as in the composite weigh-meter/rotary-valve feeder described above (Weigh Meter Feeder Principle) for use in primary resin production and compounding.

Delumping
In some primary resin applications where delumping of the virgin resin is required, a highly specialized and ruggedized variant of the basic rotary valve principle is needed, called a delumper. Robustly designed and hydraulically driven for high-torque, low-speed operation, the basic rotary valve principle is adapted for use in delumping through the addition of slightly angled hardened knives positioned above the rotating vanes to shear the lump, reducing its size. Pocket dividers may be employed as necessary to limit the maximum size of pieces allowed to pass through the unit.

If jamming should occur, special anti-stall control temporarily applies increased torque for the advancing knife to shear the jam. If unsuccessful, rotation is automatically reversed to relieve the jam and attempt shearing in the opposite direction against the retreating knife. This process is repeated several times prior to initiating an alarm if the jam persists.

Typically, bearings and pockets are nitrogen purged, and heat tracing and blanketing systems may be required depending on application specifics.
 

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