The objective of truly effective maintenance and service programs is to significantly reduce downtimes, improve safety and ensure hydraulic direct-drives maximize their operational value.
By Timothy McCrea

Large hydraulic direct-drive systems are often used in industrial recycling operations where heavy materials are processed with extreme force. Ideal for shredders, hammer mills, rollers and other machinery, radial piston direct-drive hydraulic motors are characterized by their variable low-speed/high-torque capabilities, ability to withstand shock loading and reliability in difficult operating conditions.

Maintenance inspections can capture data about machine performance to improve production processes. Weekly inspections should document danger signs, such as main pump pressure changes, fluctuations in desired motor speed, increased oil temperatures compared to standard operating levels, increased case drain flows, hydraulic oil leaks and oil reservoir levels.

Basics of Hydraulic Direct Drives
Low-speed/high-torque radial piston motors can produce extremely high amounts of torque from a relatively compact package. In general, the radial piston motor mounts directly on the machine’s driven shaft while the other hydraulic drive components, such as the pump and reservoir, can be located away from the machine.

Some of the better radial piston hydraulic drives are designed to prevent equipment damage via set points and limits that prevent over-torque. Diagnostics and machine health indicators are additional advantages available on these types of radial piston hydraulic drive systems.

Avoiding “Breakdown Maintenance”
Hydraulic direct-drives are engineered for longevity. However, implementing a few effective preventative maintenance best practices can prevent major breakdowns and save time and money versus shipping off a damaged system to a repair center.

Without routine preventative maintenance practices, even the best hydraulic system will break down. What follows is called “breakdown maintenance,” which can have serious consequences, such as:
• Equipment deterioration from neglect, increased energy costs and reduced efficiency
• Small issues—such as fluid leaks from worn-out seals—become big issues
• Safety incidents and injuries occur more often due to sudden equipment failures or jams
• Maintenance teams are pressured to make repairs on a time crunch, potentially overlooking standard safety practices
• Emergency repairs are more difficult to schedule and can take personnel away from regular duties
• Failures in multiple pieces of equipment can happen right on top of each other

Best Practices for Maintaining Hydraulic Direct Drives
Consistently following several key maintenance practices can prevent many potential hydraulic direct-drive failures and keep you from operating in “breakdown maintenance” mode.

Radial piston direct-drive hydraulic motors (shown here in orange) are well-suited for recycling operations because of their low-speed/high-torque capabilities, long-lasting performance and reliability for working with heavy loads under difficult operating conditions.

Periodic Inspection and Maintenance Checks
Equipment inspection intervals should be monthly at a minimum, whereas some facilities conduct weekly inspections. Document danger signs, such as main pump pressure changes, fluctuations in desired motor speed, increased oil temperatures compared to standard operating levels, increased case drain flows, hydraulic oil leaks and oil reservoir levels. These inspections not only prevent breakdowns, but can also capture machine performance data to improve both the maintenance and production processes.

Hydraulic Fluid Selection and Condition
Follow the hydraulic manufacturer’s recommended fluid viscosity rating and consider environmental factors. Recycling operations may have temperature extremes based on their locations, especially in high-temperature environments. In these locales, be sure to double-check the hydraulic system specifications to determine whether changing from a moderate viscosity fluid to a denser viscosity is permissible.
It is also important to regularly monitor hydraulic fluid for contaminants, discoloration or particles, especially in operations generating a high level of dust or other contaminants. Oil condition is a critical warning sign that motor components may be worn or damaged.

Servicing Filters and Seals
Change hydraulic filters at specific intervals to reduce any contamination buildup that can cause premature wear in all hydraulic system components. Direct-drive manufacturers will specify the type of filter their system should use and may provide more detailed recommendations—filter medium and micron level, for example—depending on the level of dust and contaminants present in the operating environment.
In addition, most hydraulic systems have fittings that use O-rings to prevent leakage. However, due to the shock loading and vibration inherent in recycling operations, these O-ring seals may tend to wear out more frequently. Periodic inspections will identify those leaks so you can replace worn O-rings, tighten loose fittings or replace any damaged fittings.

Use OEM Parts
When radial piston motor repairs are needed, do not assume that the local repair vendor has the expertise to bring the motor back up to the proper operating specifications. To achieve an OEM-level specification, it is critical to ensure the right parts are used. It is quite common to see motors repaired with used parts taken from a scrapped component or with aftermarket parts that are not designed to perform under the harsh conditions of high shock load equipment. In addition, sometimes motors have internal wear parts that require a proprietary coating that may improve service life or efficiency. This detailed knowledge may not be available from third-party local repair shops working on a wide range of industrial hydraulic equipment.

Be sure to specify that any repairs should use original OEM parts supplied from the manufacturer and not those pulled from a scrapped motor. In fact, some hydraulic direct-drive manufacturers1 do more than repair their equipment: they can provide fully remanufactured drives and radial piston motors with “like new” warranties to ensure long-term performance.

Filter changes at specific intervals are important to reduce contamination buildup and, in turn, reduce wear in all hydraulic system components.

Choose OEM-Certified Service Suppliers
The specialized design and operating characteristics of hydraulic direct drives call for a higher level of expertise and resources, which is usually best supplied by OEM-certified facilities that concentrate on this equipment. Third-party repair facilities will not have the original manufacturer specifications to properly repair, calibrate and test the motor to new condition—and, in fact, will not typically be able to perform a fully warrantied remanufacture.

OEM-certified facilities can also provide factory-trained technicians to inspect, service and maintain the OEM’s equipment. Certain proprietary components that cannot be duplicated or obtained from scrapped drives and motors may only be available from OEM-certified facilities; in addition, there may be specific equipment tolerances that only the factory or OEM service shop are equipped to work with.

Preventative Maintenance Programs
Many of the best practices described here can be incorporated into comprehensive preventative maintenance (PM) programs that identify risks and correct issues before they lead to failures or downtimes. Effective PM programs include annual major inspections and quarterly minor inspections carried out in the field by factory-trained and certified technicians.

Good PM programs include detailed inspections of all accessible equipment, oil temperature, pressure and non-intrusive motor temperature inspections, pump settings, speed and motor parameter setting inspections and validation against operating specifications, case drain flow measurement, oil analysis as well as shaft coupling and O-ring inspection and replacement. An effective PM program will also supply a detailed report of findings, recommended maintenance, required spare parts and follow-up actions.

Work with Experts
Hydraulic direct drives are engineered to provide years of service, even in demanding recycling operations, which is why proper maintenance programs from service facilities operated or authorized by the equipment’s OEM make the most sense.

These facilities have the technical personnel, direct access to the manufacturer’s parts and field experience necessary to keep hydraulic direct drives operating smoothly through their full lifecycle. In addition, they can advise recycling operators when it makes sense to retire legacy equipment once it becomes cost prohibitive to continue remanufacturing.

A Final Note on Maintenance
As with any system in a rugged environment, routine service is critical to maintaining the uptime of radial piston motors. The objective of truly effective maintenance and service programs is to significantly reduce downtimes, improve safety and ensure hydraulic direct drives maximize their operational value. Following these tips, from fluid checks to working with an authorized repair expert, will help achieve that goal and prevent major breakdowns. | WA

Timothy McCrea is Market Segment Manager – Aftermarket, for Hägglunds – Bosch Rexroth Corp. He brings more than 20 years of experience in multiple technology disciplines including Electric Drives and Controls, Linear Motion, Pneumatics, Industrial Hydraulics and 13 years of experience in the Power Transmission Industry. He has developed and implemented numerous Aftermarket National Account agreements with Fortune 500 companies to help improve machinery uptime, reliability and cost savings. Timothy can be reached at [email protected]. For more information, visit

1. Such as the Hägglunds group from Bosch Rexroth