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New seal option helps extend life of workhorse motor

Eaton Delta motor with Extreme Duty Seal Guard

A reliable workhorse motor has become even hardier with the introduction of a new seal protection option. Eaton's Delta motor, introduced nearly 10 years ago, is now also available with an Extreme Duty Seal Guard to help protect motors operating in grubby environments. The Extreme Duty Seal Guard can outlast a traditional slinger seal four times over, keeping dirt out of the motor and extending motor and machine life.

Reliability has long been the holy grail of hydraulic motors, with dirt intrusion one of the key causes of motor failure. When a motor fails or runs poorly, unwelcome events inevitably follow. Fluid may leak and contaminate vegetation or soil. Pumping may slow or stop, causing equipment to malfunction. Credibility with customers may suffer for manufacturers, distributors, and service providers. In short, motor problems not only prevent completion of critical tasks, but can lead to large, unwanted repair costs and other negative consequences.

The Delta motors are part of Eaton’s Geroler® family of motors, which provide extraordinary performance in both mobile and stationary hydraulic systems. Whether for a new application or a drop-in replacement, Delta motors employ the latest technology to keep systems running smoothly. Applications include traction drives for turf care, brush drives for sweepers, and auger drives for construction.

Achieving greater reliability

Seals are one of three main components where Delta motors offer improved reliability; drives and bearings are the others. Drive life is extended through a combination of advanced technology and a simplified design. Delta motors feature a two-zone design, where oil enters one zone and exits from another. While other hydraulic motors include a case drain port as a third zone, the Delta motor architecture makes the third zone unnecessary. With fewer components and potential failure points, the Delta design improves reliability at the outset and offers more trouble-free operation throughout its life.

A proprietary drive design reduces wear, preventing drive chip fragments from flowing into pump. The drive design improves drive angles by mimicking the eccentric motion of the star-shaped rotor, as the star rotates and oscillates. This helps translate the torque to the pure rotation of the output shaft. 

The Delta architecture also locates the valve in the middle portion of the motor, as shown in Figure 1. This more optimally balances the length of the motor with life of the drive. By having the valve in the middle of the motor instead of the end, the motor’s overall length is reduced without compromising the strength of the drive. Competing designs, with the valve in the rear of the motor, have a shorter drive which increases stress at high torques, and route flow through a hole in the middle of the drive. The Delta’s solid drive design also allows for higher strength and more uniform heat treatment during manufacturing.

Figure 1. The Delta motor features enhanced drives, seals, and bearings to extend life

 

Figure 2. Delta motor life exceeded 200 hours in testing, with one sample reaching 700 hours

The robust drive design translates into longer motor life. In newly released multiple-sample testing, the Delta motor life exceeded 200 hours, with one sample reaching a life of 700 hours, as shown in Figure 2.

Bearings also play a key role in motor longevity, as they transfer loads from the shaft to the motor frame. To extend bearing life, Eaton partnered with premium suppliers to select durable, properly sized bearings. Thrust bearings on Delta motors are capable of withstanding up to 2,000 psi back pressure. Heavy-duty roller bearings are ideal for handling machine loads in propelling applications. The mid-mount valve design again provides an advantage, here, allowing for the bearings to be farther apart, which extends loading capability farther from the mounting flange.

The extended bearing life has been quantified in testing to determine the L10 bearing life, which is the life at which ten percent of the bearings in a given application can be expected to fail due to classical fatigue failure. As shown in Figure 3, Delta bearings handled over 11,000 radial pounds in L10 testing, versus approximately 8,500 lbs. for a competing product.

Bearings also play a key role in motor longevity, as they transfer loads from the shaft to the motor frame. To extend bearing life, Eaton partnered with premium suppliers to select durable, properly sized bearings. Thrust bearings on Delta motors are capable of withstanding up to 2,000 psi back pressure. Heavy-duty roller bearings are ideal for handling machine loads in propelling applications. The mid-mount valve design again provides an advantage, here, allowing for the bearings to be farther apart, which extends loading capability farther from the mounting flange.

The extended bearing life has been quantified in testing to determine the L10 bearing life, which is the life at which ten percent of the bearings in a given application can be expected to fail due to classical fatigue failure. As shown in Figure 3, Delta bearings handled over 11,000 radial pounds in L10 testing, versus approximately 8,500 lbs. for a competing product.

Figure 3. Delta bearings handled over 11,000 radial pounds in L10 testing.

Seals have provided the most recent opportunity to further extend motor life. Hydraulic motors generally employ two types of seals – one to keep oil in and another to keep dust and dirt out. Holding the oil in the motor is the function of a pressure seal, which can be designed to withstand various pressures, depending on the application. 

Pressure seals are sensitive to dirt and other contamination, so an exclusion seal is used to protect it from the outside environment. 

These seals have a similar look to pressure seals, but are installed in reverse to keep typical contaminants out. A standard exclusion seal includes a rubber seal on the motor shaft that will keep dirt out for most applications. For harsher applications, such as sweepers or conveyers, a slinger seal, as shown in Figure 4, provides an additional layer of protection. Working in tandem with the standard rubber seal, a slinger seal is pressed onto the motor shaft, and rotates with the shaft to better protect from weeds, and stringing material, dirt, rocks or direct contact, like the water stream of a power washer. Delta shaft seals are made of hydrogenated nitrile butadiene rubber (HNBR) capable of withstanding high pressures and speeds.

Figure 4. Slinger seal (depicted in red) is pressed onto the shaft and rotates with it to improve protection for the pressure seal.
Figure 5. The Extreme Duty Seal Guard includes a stationary housing (depicted in green) as well as a metal shield rotating with the shaft (depicted in gray).

The slinger seal has been considered the industry standard for motor protection in dirt-ridden applications. This seal has performed well over the years, but has limitations when the motor is exposed to fine dust and fluids that can wash behind the rotating guard. 

The new Extreme Duty Seal Guard option was introduced earlier this year to help protect equipment operating in strenuous conditions, such as sand vehicles, fertilizer spreaders, tillers, and anything requiring a power wash down at the end of the day. An industry first for hydraulic motors, the Extreme Duty Seal Guard is a two-piece design, as shown in Figure 5, with a pressed-in stationary housing as well as a metal shield rotating with the shaft. It keeps the effective shield of the slinger/seal guard, but adds three additional lips packed with grease to keep dust and liquidus fluids out.

Even without the Extreme Duty Seal Guard, test data support the Delta seal design’s effectiveness in extending seal life. Based on accelerated seal testing shown in Figure 6, the Delta shaft seals lasted over three times as long as seals in a competing motor. A counterclockwise direction was used for 95 percent of the testing duration, as this presents more challenging conditions for two-zone motors. With the Extreme Duty Seal Guard, seal life was extended by four times over the slinger seal, as it did a superior job of preventing contamination from reaching the pressure seal.
Figure 6. Delta seals performed successfully for more than three times as long as seals in a competing motor.

Efficiency

In addition to greater reliability and durability, the Delta motor offers a high-efficiency solution. The Delta’s balanced valve design reduces high-pressure warping, increasing volumetric efficiency. The valve is precisely sandwiched between the balanced rings and the valve plate, avoiding excessive pressure that might cause the rotating valve to act as a brake. Other valves tend to deflect under high pressure, leading to lower volumetric efficiencies at high speeds, which typically affects top-end machine speeds. 

High-flow valves also provide high mechanical efficiency. Eaton disc valve motors allow higher flows and pressures than spool valve motors, making the Delta motor a natural upgrade to traditional motors.

Optimized balanced rings maintain high efficiency in both directions, which is critical on two-zone motors, where one motor is typically used for each wheel. If an OEM only wants to carry one part number, when traveling in a forward direction, one motor will be running clockwise and the other counterclockwise. If the motor’s valving is not truly bi-directional, the vehicle may drift in one direction.

Side-load capacity

Delta motors provide excellent side-load capacity due to the front radial bearing design. This is a key feature for turf applications, where extreme loading conditions can occur, both during operation and transportation of equipment. Turf equipment is often transported by trailer, with the machine ratcheted or chained down. The tie-downs can exert extreme static loading on the shaft, potentially damaging bearings or causing enough deflection to create a seal leak. During operation, other severe loading conditions can be encountered, as equipment is operated over rugged terrain and other challenging situations.

Anyone who has experienced problems with hydraulic motors will likely appreciate the value of increased reliability. The resulting gains in performance, credibility, and peace of mind, along with potential cost savings, can clearly support decisions to switch to a more reliable motor. Benchmarked off competing motors, the Delta was specifically designed to be a superior motor for similar applications. These same benefits can also be realized in new product decisions, or where equipment has been operating satisfactorily. The already proven reliability, increased efficiency, and enhanced side-load capacity can make the Delta motor a trustworthy choice for new systems or as drop-in replacements. The increased protection of the Extreme Duty Seal Guard can make the Delta an even more robust choice. Eaton is so confident in the Delta’s performance that it is offering free prototypes to qualifying customers. For more information, contact an Eaton representative at www.eaton.com.