Help me understand my Steering system

[timjet]

I’ve never really understood how my steering system works. I have a helm pump behind the steering wheel with hydraulic lines running to an actuator that’s connected to a tie rod that moves both rudders.
My question here is how does the helm pump provide the necessary hydraulic pressure to the rudder actuator. The steering wheel is very easy to turn without much resistance.

Second question, how does the autopilot control the steering. On my system I have all Raython equipment. The autopilot control head is a Raython ST-6000+ and there is also a type 100 course computer. Electrically connected to the course computer is an auto-pilot motor, a flux gate compass and the ST-6000+ control head. Additionally the course computer has a sea talk input from the chart plotter and ST50 Tri Data depth and speed gauge.
When the autopilot is engaged it somehow disengages steering from the wheel. I can turn the wheel but there is no response. Of course when the A/P is off steering is back to the wheel.
So presumably the autopilot motor engages the helm pump and at the same time disengages the wheel. I never hear any clicking or engaging/disengaging of relays or solenoids when this happens.

Can anyone shed some light on this.

 

[twistedtree]

The helm pump works just as you suspect - rotating the wheel pumps oil down a line and forces the steering cylinder in one direction. Turning the wheel in the other direction forces oil down the other line and forces the cylinder in the other direction.

The auto pilot pump does the same thing, except it's controlled by the AP computer.

The reason the helm wheel doesn't move with the AP steering is because of check valves. The outputs of the steering pumps have check valves (one-way valves) that prevent back-flow. When one pump is pumping, the check valve on the other pump prevents fluid from flowing into the pump, so the only place it has to go is the steering cylinder.