Hydraulic steering fault

[Bodach na mara]

Thanks again for the diagram Roger. It has helped me to understand how these things work. Before that, all I had to go on was an old Morris oil pump of the two-gear lobe type which I took to bits. At least I could understand how the ports allowed a reversible directional flow from that.

Now has anyone found a diagram for the Vetus pumps? It seems that they are of a radial cylinder type as you can see the cylinders going round through the filling cap like the cylinders in an old rotary aircraft engine (where the prop was attached to the cylinders and the crankshaft was fixed to the aircraft.)

 

[rogerthebodger]

No the Vetus one is an axial piston pump simular to the one in my diagram.

The main practical difference is that with an axial pump it is very easy to change the flow per rev than in a radial. also radial tend to be bigger in dia and short in lenght axial are the other way round.

The angle plate in the side view is the swash that controls the flow per rev which in the Vetus one is fixed but adjustable in the one in the diagram.

The pump are truely bi directional so no special valveing needed. If in the OP's arrangment the rudder can be moved which turns the wheel that would mean that no pilot check valves are fitted so I dont knlw how the auto pilot pump would work unless the main wheel was locked to stop it turning.

 

[EuanMcKenzie]

more info

Vetus have confirmed the pump or cylinder to be an MT100 (they wern't clear which - maybe both) and it is similar to the drawing above. It has two ports on the outlet shaft one releasing fluid and the other supplying return fluid.

The cetrek pump was added by the previous owner but has been there circa 10 years and all the time I have had the boat. when it works the wheel turns too. That said it hasn't worked for a long time due to other problems with the autopilot system. I have the bits to sort it now.

It is installed in accordance with the Cetrek manual.

I have a small header tank in the pedestal and am wise to the missing fluid issue. Been there previously and I know its not that. I check it regularly and its the first place i look if i have a steering problem.

Going to try and dismantle the cylinder this weekend but its not obvious how it comes apart. Has anyone got a drawing or advice on how they strip down.

Picture of the cylinder attached to assist.

Euan

 

[rogerthebodger]

"Going to try and dismantle the cylinder this weekend but its not obvious how it comes apart. Has anyone got a drawing or advice on how they strip dow"

If your cylinder is like mine it has a spring that sits in a 2 half circular groves on the inside of the cylinder tube and the outside of the end cap spigot. the end cap spigot also has an o-ring to seal the end cap.

Have a look for 2 small holes drilled at and angle in each end of the cylinder tube. Inside is a spring that must be removed by pushing the spring and twisting the end cap in relation to the cylinder tube. Not easy. I ended up taking mine to a local hydralic cylinder repair shop mainly due to the pitting in the cylinder rod that was damaging the rod seals on my cylinders.

Good luck and do let us know how you get on.

 

[maxi77]

Without seeing the precise circuit it is difficult to diagnose the problem, but if no oil is being lost there is clearly leakage from one side to the other, this can be either in the pump. the steering ram or the autopilot pump. Commercial systems tend to have cross linked check valves on the steering ram to hold the rudder in the selected position which stops the autopilot forever hunting to keep the boat on course, I would have thought that this system would have had the same for the obvious reasons, otherwise the autopilot will be for ever pumping and all that happens is the wheel turns.