The 28 cm³ constant motor, in plain terms

The A10FM 28 is a swashplate axial piston motor with a single fixed displacement: 28.5 cm³ for every turn of the shaft. Nothing about that displacement can be altered - flow in means speed out, and the pressure difference across the two working ports becomes torque. Drives that must repeat the same motion cycle after cycle, in open circuit or closed circuit, are the natural home for this design.

The rotating group is the long-established A10 unit, run at medium pressure. Because the size sits between the two neighbouring frames, it is often the compromise answer to a fairly common question: how much torque can be obtained without losing the ability to spin fast?

Where 28 sits: 23 versus 28 versus 37

All figures at 280 bar nominal pressure and full displacement. Rows 23 and 37 are shown for reference only, both from the same data sheet.

Numbers you will be asked for

Interfaces and build options

Before the first start

• Fill the housing before the shaft is first turned. Every mounting attitude is permitted, but the drain line must not be able to siphon the case empty while the machine stands idle.
• Feed port A for clockwise rotation seen from the drive end, port B for the opposite direction.
• Run HLP fluid to DIN 51524 and hold the circuit at 20/18/15 ISO 4406 or cleaner. Should drain-port viscosity slip under 10 mm²/s, the tighter class 19/17/14 takes over.
• Efficiency peaks between 16 and 36 mm²/s. In service the motor accepts 400 down to 10 mm²/s, briefly 7 mm²/s, and up to 1600 mm²/s from a cold start. Fluid at port LX stays at or below 110 °C.
• Respect the floor pressures as well as the ceiling: at least 10 bar absolute on the loaded port, at least 2 bar absolute on the return side, and no more than 2 bar absolute standing pressure at L / L1.

Three questions buyers send us

To price a unit we need four things: shaft end, port variant, valve and sensor options, and the quantity. Add the machine duty if you also want the displacement checked.