I recently tried out a brand new Hydrema 922D articulated dump truck and Infracon kindly allowed us to test the machine in its quarry, giving the ultimate range of conditions for the Hydrema to prove itself — and it did!
Cab and controls
Access up to the cab is aided with decent-sized steps and handrails, making the climb safe and easy. The Hydrema’s cab gives great all-round visibility with plenty of glass and narrow cab pillars. An unobstructed view to the front and sides is obtained and helped further by a sloping engine cover. An air-suspended seat soaks up the remaining bumps from the visco-elastic suspended cab mounts, giving a very smooth ride in all ground conditions. Most of the switches are conveniently mounted on the two right-hand cab pillars, allowing them to be easily identified and reached. With the press of a button, the right-hand joystick raises and lowers the body. Incorporated into the top of the joystick are forward/reverse and plus, minus and neutral gear selection buttons. A holding brake for use when tipping the body is included. Large mirrors provide a good view to the rear. These are heated and can be electrically adjusted by controls in the cab.
Engine, hydraulics and driveline
A six-cylinder 264-horsepower Cummins engine is fitted with a six-speed forward, three reverse ZF transmission and torque converter and features 100% lock up in all the gears. An exhaust brake and hydraulic retarder provide some deceleration to help slow the Hydrema without constantly relying on the service brakes. Four hydraulic pumps provide the oil for all the hydraulic functions, including a dedicated pump for emergency steering.
Design and maintenance
The Hydrema has been well designed and built to last, quality Hardox steel is used in the construction of the dumper body and features a very steep tip angle of 72 degrees for a full discharge of sticky material in a fast time of 7.5 seconds up and 5.5 seconds down. To achieve a low tare weight while retaining durability, high tensile steel is used in the fabrication of the chassis. The engine bonnet electrically opens up for easy access to the engine and cooling system and opens well forward to provide maximum room. Unique to Hydrema is the pendulum bar centre pivot with double hydraulic stabilisers This design ensures excellent stability while driving and when tipping the body and allows +/- 12 degrees oscillation. An auto-grease system is fitted to provide constant lubrication of the pins, dramatically increasing their service life.
Performance and handling
When loaded, the 922D is amazingly smooth to ride in, even when travelling at a variety of speeds over undulating ground. Driving empty gives a similar ride up front, but the rear bogie tended to bounce a bit as they usually do on rough ground. The electronically-controlled hydraulic front suspension soaks up the bumps very well and provides an exceptionally smooth ride in the cab, assisted by an air-suspended seat that is very comfortable and has plenty of adjustment. The steering wheel is also adjustable, so getting into your favourite driving position is simple as all the controls are well placed and easy to reach.
The Cummins engine provides plenty of punch and doesn’t give in without a fight when pulling fully-loaded up the steep haul roads out of the quarry. The engine holds on down to 1450rpm before the six-speed ZF transmission smoothly reaches for a lower gear.
I did a few runs shifting heavy, sticky overburden from the benches over to the tip site before going down into the bottom of the pit to haul out some aggregate. The circuit had a bit of everything for the Hydrema to prove itself — steep climbs, faster flats and some tighter manoeuvring, but it seemed nothing to the 922D as it went about its work.
Fully loaded, I leave the Hydrema in auto mode to see what its decision-making skills are like. It handles very well, and quickly and smoothly accelerates to a good speed on the flats. When it comes to stopping, the exhaust brake and hydraulic retarder help slow it down, assisted by the automatic downshifting of the transmission. The ZF box is equipped with full lock-up in all gears, bypassing the converter and giving direct-drive makes for a more fuel efficient machine and allows for maximum engine braking.
The transmission can be operated in auto or manual modes. I left it in auto throughout the cycles but chose manual to ensure there wouldn’t be an unexpected upshift when descending the steep roads — though on a safe part of the decline I flicked it into auto and it held its gear without upshifting, which was very reassuring.
Throughout the trip the Hydrema remained smooth and nimble and was very operator friendly. Driving down into the pit empty, the exhaust brake held back the almost 16-tonne dumper with only a couple of dabs of the hydraulic retarder to assist on the steeper parts.
With a full load of rock on, the 922D pulls away from a hill start with ease. It grabs second gear as the road momentarily flattens and then continues to accelerate up the increasing climb. It stayed in second gear at full revs until the top. Though third would have been too big a jump, it would have easily handled a steeper road in second gear.
The cab remains very quiet throughout the whole rev range and is a pleasure to be in for both comfort and visibility. A rear view camera and large mirrors make reversing simple, as a clear view behind the machine is obtained.
The single joystick contains driving and tipping controls. Included in this is the holding brake. This is such a convenient feature and allows the brakes to be applied while tipping the load. Should the machine need to be moved forward during dumping this is all done from the same joystick — there is no reaching or looking for controls, so your eyes are focused on the job, giving a far quicker reaction time should matters arise.
The steep tip angle makes even this sticky wet overburden slide out without getting hung up, meaning there is no carry back so the efficiency levels are kept high. Oil immersed disc brakes provide superior stopping performance and are smooth even under heavy braking — not good practice but its nice to know they work well. I found the Hydrema 922D to excel in design and build quality. It is extremely quiet and comfortable to operate and has plenty of power, giving fast cycle times. Its light yet strong design gives the best of both worlds.
Photography: Tim Dittmer