Decanter Centrifuge Spare Rotating Assemblies Explained

A decanter centrifuge as a complete piece of equipment used for sludge dewatering and sludge thickening includes - a centrifuge frame, the housing, control panel, main motor, back drive (hydraulic or gearbox), lubrication system, and a variety of sensors, solenoids, and monitors, and last but not least “the guts'' or the rotating assembly (RA). The rotating assembly has two main components: the centrifuge bowl and a scroll (screw conveyor). An electric motor drives the bowl. The internal scroll, which operates at a slightly different speed than the bowl (this is called differential speed), is driven by a radial piston hydraulic motor.

It's essential to understand the different centrifuge service and repair solutions available and how they can make a difference to your operation. One option is having a spare centrifuge rotating assembly at your plant or partnering with a centrifuge manufacturer that thinks outside-of-the-box to offer spare RA repair solutions.

What are the advantages to having a decanter centrifuge spare rotating assembly?

First, and foremost a spare rotating assembly will minimize sludge dewatering or thickening downtime at your plant. Typically, a spare assembly can be exchanged on-site in six to eight hours. If uptime is critical, a spare RA should be included in your plant’s equipment inventory. 

A spare RA allows the damaged assembly to be inspected, repaired, and optimized correctly. As a result, plant operators are not pressured to repair an assembly too quickly. A quick repair will almost always lead to a “band-aid” fix that can cause significant problems later.     

Let’s review more advantages and what's important to know with each type of spare rotating assembly.

1. Bearing to Bearing

The Bearing to Bearing Rotating Assembly (RA) uses the existing pillow blocks (also called bearing housings). This assembly includes the inner main bearings and the bearing plates.

ADVANTAGES:

• Minimizes plant downtime
• Reusing the pillow blocks is the most flexible option when multiple centrifuges are in a plant
• If the existing pillow blocks are re-used and are not damaged, an alignment is not necessary; this is because the pillow blocks are already aligned with the centrifuge frame
• Provides the necessary time to thoroughly inspect, repair, and optimize the damaged assembly at a Centrisys repair facility

• With this assembly, the pillow blocks from the original RA(s) are used on every centrifuge in the plant
• The drive pulley, hydraulic drive, and adapter are used from the original assembly
• Before assembly of the spare RA, the bearing housings should be inspected for damage; if damage is found, they will need to be repaired or exchanged; in that case, the pillow blocks will need an alignment.
• A thorough inspection of the centrifuge is recommended after an assembly exchange

The Full Spare Rotor is an assembly that includes new centrifuge bearing housings, a new drive pulley, and the ROTODIFF adapter. 

* A Full Spare RA does not include the ROTODIFF Hydraulic Motor.

ADVANTAGES:

• Allows for a quick RA swap onsite - reducing operational downtime
• Provides time to thoroughly inspect, repair, and optimize the damaged assembly at a Centrisys service facility
• Service and repair of the original assembly include the inner main bearings and plates, drive pulley, adaptor, and pillow blocks

• Requires a one-time, on-site pillow block dial-in alignment
• After the pillow blocks are aligned with the frame, they are pinned (using a roll-pin or conical pin); the alignment procedure guarantees correct positioning after installation
• If multiple centrifuges are on-site, the dial-in and pinning procedures are necessary for each centrifuge
• A thorough inspection of the centrifuge is recommended after the RA exchange

The Complete Spare Rotor is an assembly as if it was lifted from the centrifuge frame. This version includes the centrifuge feed pipe and the ROTODIFF Hydraulic Motor.

ADVANTAGES:

• Allows for the quickest RA swap with the least operational downtime
• Provides the necessary time to properly and thoroughly repair the original RA at a Centrisys service facility
• The repair of the original assembly is the most comprehensive; it includes the inner main bearings, bearing plates, drive pulley, adaptor, pillow blocks, and back drive (either gearbox or hydraulic)

• Requires a one-time, on-site pillow block dial-in alignment
• After the pillow blocks are aligned with the frame, they are pinned (using a roll-pin or conical pin); the alignment procedure guarantees correct positioning after installation
• If multiple centrifuges on-site, the dial-in and pinning procedures are necessary for each centrifuge
• A thorough inspection of the centrifuge is recommended after an RA exchange

• Standard procedures and tooling are necessary to dial in a centrifuge rotating assembly
• When the RA dial-in is required, NEW roll pin locations are necessary; do not rely on the original taper pins or metaligner locations
• The pillow blocks have one additional location to install a set of pins
• A plant with multiple centrifuges benefits best from the Bearing to Bearing Rotating Assembly because of its versatility

It’s essential to perform routine centrifuge service and maintenance. The rebuilding of the rotating assembly should be a primary consideration with all centrifuge preventative maintenance plans. You can minimize centrifuge repair costs in the long term by working with Centrisys to recommend a centrifuge maintenance plan and spare parts inventory.