Marine Technology Group

ASD Control Systems

STEERING CYLINDER CONTROL MANIFOLDS

Aside from the steering functions, other steering control functions are required for issues such as steering cylinder relief, isolation of a failed steering cylinder or the use of a Hydraulic Tie Bar for certain catamaran applications.

Steering Cylinder Relief Manifolds

Steering Cylinder Relief Manifolds are used to allow the hydraulic pressure to return to the reservoir in case of abnormally high loads are generated.  These loads are generated on certain ASD applications due to the geometry of the ASD Thrust Unit, Steering and Trim Cylinders.

Steering Cylinder Isolation Manifolds

Steering Cylinder Isolation Manifolds are designed for use on hydraulic steering systems equipped with two (2) opposing steering cylinders connected with a mechanical tie bar on Arneson Surface Drives.  The manifold provides a method to isolate either one of the two steering cylinders from the steering system in case of a cylinder or external hose failure.  In addition to isolating a failed steering cylinder the manifold has ports for connecting a second helm unit.  The helm units are isolated from each other through the use of pilot operated check valves.

Hydraulic Tie Bars

Hydraulic Tie Bar Manifolds (HTB) are designed to be used on vessels equipped with Arneson Surface Drive systems using power assisted hydraulic steering systems equipped with two (2) opposing steering cylinders, not connected with a mechanical tie bar.  The manifold provides a method to adjust the toe in/out of the cylinders.  The HTB system is designed for use on vessels where there are constraints in using a mechanical tie bar, such as on catamarans.  The distance between the ASD centerlines should be sufficiently wide enough so that there would be no mechanical contact between the ASD system or propellers, in case of a hydraulic hose failure.

  The HTB uses the pressure generated  on the opposite side of the cylinder piston that is steering, to generate the pressure in the HTB loop and furnish the necessary pressure to steer the opposite cylinder.  In most cases the steering is accomplished using the "rod" side of the cylinder.  The "large end" of the cylinder is used for the HTB function.  If this orientation is not observed, in some cases pressures can be generated in excess of the system proof pressure.

It is important to maintain positive pressure in the HTB loop through the rotation of the propellers.  This means that when viewing the vessel looking forward, the propellers rotate into the cylinders.  Rotating the propellers in the opposite direction can cause a negative pressure in the HTB loop, resulting in a system that does not operate properly.