An electronically controlled version of Parker Denison's XL-75 pump contains a sensor package that provides control modes that are impossible or impractical with conventional hydraulic controls.


Smart valves and smart cylinders have been around for years. What makes these components smart is spool or piston position feedback, so the components become active participants in a control loop, rather than dumb slaves that simply respond to a command.

A smart pump, though, would require more than simply providing position feedback, which would be an indication of displacement. A truly smart pump would have to incorporate feedback of both displacement and pressure. Denison Hydraulics (now Parker Hannifin's Hydraulic Pump Div.) has done just that with its XL-75 axial-piston pump. This medium-duty, open-circuit pump features variable displacement to 75 cc/rev and optional digital electronic controls for

  • pressure limiting,
  • displacement,
  • torque limiting and summing,
  • load sensing, and
  • anti-stall speed.

The heart of the digital electronic control system is a fully integrated, factory-calibrated sensor package containing onboard electronics and multiple sensors. The sensors monitor pressure, displacement, speed, and temperature.

The onboard digital electronics work seamlessly with the integrated sensor package to provide all the control modes available on pumps with conventional hydraulic controls and more. These additional modes had been considered impossible or impractical using conventional technology.

The electronic version of the XL-75's housing is machined to accommodate the compact digital electronic cube that contains all the required control hardware.

A PC interface provides access to the pressure, displacement, power, and speed settings that allow customizing a pump to a particular application. It also provides access to diagnostic information with a data acquisition mode that can display and store real-time operating conditions. Furthermore, it provides access to change control modes of the pump. This means a single XL-75 electronic pump can replace many different pump models limited by conventional controls.

Denison's XL line eventually will encompass ten models, ranging in maximum displacements from 10 to 260 cc/rev and rated to 280 bar (4060 psig). In addition to the new electronic version of the XL-75, Denison also offers conventional 75-cc and 140-cc versions. These two pumps provide pressure limiting, load sensing, and pilot-operated control when equipped with an ISO 4401 interface.

Small power unit runs on tap water

A new hydraulic power unit from Danfoss Graham runs on electricity, but it uses pure tap water as the hydraulic fluid. As with all the Nessie components and systems from Danfoss Inc., the small HPU is designed to be used with ordinary tap water as the pressure medium at pressures to 2000 psi. Standard flow ratings are 1, 2, or 3 gpm.
According to Tom Foster of Danfoss Inc., Milwaukee, the HPU is designed to power hydraulic cylinders and motors that can use tap water as the hydraulic fluid. He says tap water hydraulics is a viable alternative to other technologies in situations where
• potential oil leakage is critical,
• pneumatic cylinders cannot give enough force, and
• electrical motors have to operate in a wet environment.
Power packs for larger flows, control valves, cylinders, and motors are also available.

For more information on the power units, contact Danfoss Graham, a division of Danfoss Inc., Milwaukee, at (414) 371-8468.