High Speed and Low Speed Parker Gerotor Motors: What are the Differences?

Blog | November 22nd, 2018

When Low-Speed Parker Geroter Motors run, they deliver massive quantities of torque. It’s this architecture that expedites traction-intensive fluid equipment applications. Tractors, construction equipment, forestry tools, they all benefit from LSHT (Low-Speed High Torque) hydraulic motor configurations. Interestingly, compared to their high-speed cousins, slow rotating gerotors are functionally different from their opposite numbers. Beginning with rotational velocities, high-speed Parker Gerotors have access to 7,500RPM of spin.

Rotary Velocity Discrepancies

Clear-cut system performance expectations compel hydraulic equipment designers to look closely at HSLT devices and their rivals, the LSHT category. Taking the BH series of low-speed motors as a prime example of this principle, their interior architectures rotate at no more than 660-RPM. For that lower speed, however, the equipment kicks out lots of torque. Starting torque can easily surpass 1268-Nm of intermittent output force. Running to the opposite end of the orbital motor scale, a high-speed counterpart typically delivers 30-Nm of output torque, but that figure is supplemented by a high level of discharge thrust.

Deconstructing the Architectural Variations

Going by the numbers, this approach only reveals so much. Inlet forces, venting energies and discharge power are measured in this way, and their release does tell a story, one that can be interpreted by engineers. All the same, we’re not really seeing the mechanical differences, which do exist between LSHT and HSLT actuators. For starters, there are piston configuration designs that favour Low-Speed Parker Gerotors. The pistons compress and expand at right-angles to the motor drive shaft. That’s clearly a layout that works best in low-speed equipment. For HSLT gerotors, the piston architecture is quite different. Instead of a perpendicular layout, the mechanism employs what’s known as a bent-axis piston configuration. Bent-axis architectures work better in high-speed, high-power density equipment.

Parker Motor Selection Criteria

Equipment designers are in a unique position when they’re building gerotor motors. They work backwards from the application. In effect, they’re looking at the load characteristics first. Accounting for the speed and torque of the application, they select a radial piston motor (LSHT) or a bent-axis motor (HSLT) variant. Operating pressures and flow rates are weighed. Next, what about the shaft diameter and equipment materials? Variable or fixed displacement, the load behaviour and inline performance characteristics are added to the specs list, too.

At the end of the day, Parker Gerotor Motors fall into two separate camps. If the fluid motor rotates rapidly, the laws of energy conservation reduce torque output. Counterbalancing the design principle, low-speed gerotors generate proportionally larger quantities of heavy-equipment shifting force. Internally, it’s the piston geometry that separates the two equipment types.

Mobile Hydraulic Specialties Pty Ltd

Factory 89, 38-40 Popes Road
Keysborough, Victoria, 3173

Phone: (03) 9798-6511

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