Marine Technology Group

ASD Control Systems

HYDRAULIC PUMPS

The selection of hydraulic pumps for Arneson Surface Drives is based on ASD size, number of steering cylinders and the desired response speed for steering lock-to-lock.  The data below is offered for reference and general guidance only.

H/RI recommends mounting the hydraulic pumps directly on a PTO pad on the engine or gearbox.  For some of the smaller systems, belt driving the hydraulic pump is acceptable.

It is recommended that all dual ASD steering and trim control systems be fitted with two pumps.

For open center pumps the hydraulic pump is typically oversized to insure adequate volume of fluid at engine idle.  This results in bypassing up to 75% of the fluid back to the reservoir.  Because of this, H/RI recommends open center systems for applications where a simple and inexpensive system is desired.  There is limited room for system expansion into running other circuits.

In an open center system, a fixed displacement pump delivers fluid to an open center valve. When steering is inactive, the fluid passes through the valve to the return port with relatively low pressure drop. For steering, this bypass closes to build up pressure to deliver flow through the steering cylinders.

Closed center pumps offer many advantages over open center systems.  Steering response time at engine idle is insured without the generation of excess fluid and resultant heat generation.  Smaller line sizes can be used for all primary pump circuitry.  Multiple functions such as steering ASD trim and trim tab deployment can all occur at the same time without system degradation.

In a closed center and load sensing system, a pressure compensated variable displacement pump maintains constant pressure supply to a closed center valve. When steering is inactive, the valve is closed to system flow. For steering, the system flow is controlled according to the valve opening and load pressure through the load circuit.

The pumps depicted here cover the majority of ASD applications.  For those applications such as racing, military and classed vessels, please contact H/RI for assistance as other pumps are available.

OPEN CENTER PUMPS

Eaton Series 26

These pumps can be direct or belt driven.  If the pump is belt driven, usually a smaller capacity pump can be used since the pulley ratio can be varied to utilize the maximum output of the pump.

This pump is available in three configurations:
Direct output
Direct output with built in relief valve
Direct output wit built in relief and priority valve

The series 26 pumps are field reversible for the pump direction. Simply open the pump, switch the drive gear and idler gear, reposition the plug and reassemble. No extra parts are needed.

This pump is is a good selection for a simple steering only system for applications ranging from the ASD 6 to the ASD 14.

CLOSED CENTER PUMPS

Eaton 701222, 1.6 in³/r [19 cm³/r], 70422, 2.32 in³ /r [38 cm³/r], 70423, 2.77 in³/r [45 cm³/r]

Closed Center systems are ideal when the hydraulic system requires several separate functions to operate simultaneously. The pump will maintain the high pressure and zero flow as long as the system is not actuated. When a hydraulic function is actuated, the pressure compensated piston pump senses the change in the demand for flow and adjusts the pump displacement to increase the flow required while maintaining full system pressure up to the control valve. The pump will adjust output flow to meet any change in system flow requirements.

Load sense pumps sense the pressure and flow requirements and provide only the flow and pressure required, plus 200 PSI[14 bar], to operate the compensator. This low pressure standby prevents excessive heat buildup in the pump and eliminates unnecessary horsepower drain. The pressure-flow compensated load sensing system is noted for its high efficiency and controllability.