Rebuild It vs. Retrofit: The Case for Replacing Aging Clarifier Drive Units

When Rebuilding Makes Sense

Rebuilding is not always the wrong answer. For straightforward problems at the high-speed end of a drive — a worn chain, a faulty switch, a torque mechanism out of adjustment — repair often makes sense. Motors, sprockets, chains, and belts are commercially available. The scope is manageable. The cost is predictable.

The calculation changes significantly when the problem involves major components which include gears and large bearings. That is where the decision becomes consequential — financially and operationally.

The True Cost of Rebuilding: What the Quote Doesn't Include

The consideration to rebuild typically covers the cost of

parts and shop labor. It may not reflect the full cost of the project. Removing large equipment from a clarifier requires:

• A crane and crew of millwrights
• Full mobilization to unmount the existing gearbox
• Transport to a repair facility for disassembly and inspection
• Six or more weeks of downtime
• A second full mobilization to reinstall the repaired unit

“What's often missed in the equation is the cost of mobilization. Sometimes the cost of taking out a drive unit and putting back in the rebuilt drive may be equal to the cost of the drive unit itself,” notes Nils Young, DBS Manufacturing Founder and Director.

A retrofit requires only one mobilization. The old drive comes out. The new drive goes in. The crew leaves — sometimes within 24 hours.

Rebuilding carries an open-ended scope. “Just like when you bring your car to the shop, the mechanic can't give you a quote until he's looked under the hood. Taking apart a gearbox may reveal additional problems that increase the overall cost,” says DBS Manufacturing Director of Engineering James Hu.

“What you thought might be minor rep

airs turns out to include a new gear, new bearings, new housing — essentially a new drive anyway,” adds Nils. With a retrofit, the customer has a firm price and defined timeline before work begins.

Proprietary Parts — A Risk That Will Only Grow

One main reason to choose retrofit drive units over rebuilding is that parts can be costly. "Our competitors frequently take advantage of customers when it comes to replacement parts,” notes Jorge Iduate, DBS Manufacturing Director of Engineering Emeritus. “Because most components are proprietary, customers are forced to return to the original manufacturer and pay whatever price is charged. Cast-iron components, gears and bearings that are exclusive to these units often carry excessive markups — making aftermarket parts a major profit center for these manufacturers."

Another issue to consider is that some of the original manufacturers are no longer in business. Finding exact replacement parts can be difficult today — and may be impossible in the future.

A Successful Rebuild Still Leaves You with Old Technology

 

Even a perfectly executed rebuild returns a drive unit to its original operating specifications. For older cast iron drives, that means restoring it to 1950s or 1960s technology.

Older drives were built with cast iron gears, strip liner bearings, and worm wheel gearboxes. Modern drives use forged steel gears and precision ball bearings — a substantial difference in performance, efficiency, and longevity.

“DBS drive units are about 75% efficient while competitors’ cast iron drive units are about 50%. That efficiency gap isn't seen as a problem because the clarifier is working. The tank is treating water. Everything appears fine. But the costs are accumulating quietly — in energy consumption, in ongoing maintenance, in the accelerating wear of aging components,” says Nils.

Today's retrofit technology offers capabilities that older drives simply cannot match. “For example, DBS drive units feature accurate torque indication and remote torque monitoring through a 4–20 mA output signal, allowing operators to continuously monitor drive loading and obtain valuable process data for improved operational efficiency and process control,” notes Jorge.

The Leaky Faucet Problem

Rebuilding may appear to cost less upfront. “But it is like a leaky faucet that keeps dripping. Once one problem is addressed, there will be other issues in a year or so. The initial cost may be less than a retrofit drive unit, but only in the short term,” says James.

What Retrofit Actually Looks Like

A well-engineered bolt-in retrofit drive is designed to fit the existing structure with minimal or no modifications to the bridge, rake cage, or output shaft. One drive comes out. An other goes in.

Drive replacement also creates a valuable maintenance opportunity. With the tank drained, it becomes possible to:

• Inspect rake arms, plows, and skimmer arms that are normally underwater
• Clear debris from the tank bottom
• Repair corroded or damaged components
• Relevel and adjust rake arms to run concentric and parallel to the tank floor

“This kind of full-system inspection is rarely possible during normal operation. The drive replacement window makes it practical,” says Nils.

Ready to Explore a Retrofit Solution?

In many cases, retrofitting is more economical and efficient than rebuilding. With a DBS retrofit drive unit, you get modern technology, improved reliability, enhanced performance, and lower long-term maintenance costs — and none of the disadvantages of rebuilt drive units.

DBS has been designing and manufacturing retrofit clarifier drive units for more than 50 years. Our engineers know how to build a bolt-in replacement that fits your existing structure — often faster than a rebuild would take. DBS offers a New Drive Warranty for DBS clarifier and thickener drives that includes a 10-year warranty on the drive’s main gear and bearing.

If your facility is operating aging or obsolete drive units, reach out to our engineers or contact your regional sales representative to discuss a retrofit solution tailored to your application. Visit our website to view our full product line of drive units, mixers, aerators, and industrial distributors for municipal and industrial processes.