Hydraulic steering questions

We have a old Vetus steering system and we have the following problem: when the rudder is hard over (HO) we can still force the helm to keep turning. Friends tell us that it should not be so! The helm should not be able to turn anymore, period. When we get HO, we feel a resistance but it is not that difficult to continue turning the wheel.
We thus worry than in heavy seas conditions, if the pressure on the rudder get greater, we would be able to keep turning the helm, with no effect on the rudder! No good! So we would like to solve that problem.

Here is what we did so far:
First of all, we bypassed the non-return valve box and there was no improvement We believe that the only reason of that part is to protect the pump from rudder backlash in heavy seas. Being on a mooring in protected water, we believe that part is not critical to our testing so we kept is out of the loop. Are we wrong???

We then did take the cylinder apart and replaced the internal seals that move oil one way or the other in/out of cylinder and there is no improvement

We figured that the problem then has to be the pump at the helm. First of all, we disconnected one of the 2 hoses going to the cylinder and turned the helm one way > it kept turning even as the rudder was HO. That should not happen since the hose was plugged, correct??

We then took the helm pump apart and everything looked in perfect condition (pump from 2005) .. except for a little muddy grid solidly stuck to the bottom of the reservoir housing.... I wiped it out with a rag. The pistons are shinny and move freely up and down on their springs ... the 2 small set screws on the bottom contains each a small SS ball that freely moves up or down. We are at a loss as to what other testing we can do now...

My friend thinks the oil is more viscous that it should. Vetus recommends using 22 hydraulic oil ... could the problem of the helm continuing to turn be related if the oil was thicker?? Anyone has any idea? I will go tomorrow in the small town 1 hour away but I really doubt I will find any 22 hydraulic oil ... could I use any substitute oil? compressor oil? 68 hydraulic? ... brake fluid? I will also buy some 4ft of 50bar hydraulic hose with hose clamps to try to use my pump on my frien's cylinder and then my cylinder on his pump to see if we can narrow down where the problem is ... before buying either a new pump or a new cylinder, I should know where my problem lies.

BTW Vetus Holland has not replied to my email and I read on forums that they are not interested at all to help fixing old system ... I will still try to call them this week and other specialists .. wish me luck and please share any insight if you have. Tnx

Luc

PS: we have a Vetus MTP53 pump (53cc) and a Vetus cylinder that is about 200cc volume

Yes, it does.

Thanks for your your input. We did not see any check valves in the steering cylinder but I think there are 2 small SS balls in the bottom part of the pump at the helm, that can block or not 3 small holes in the area they are set. Not sure how to find out if the problem is there or not but what you say seems to indicate that the problem is with the pump ...
Good to know that I could eventually get by AW32 oil. I do have some syntetic compressor oil ... looks thin .. wonder if that would be suitable?

Thanks for that. I just looked again on the schematics of both cylinder and pump and nowhere do they show springs (other that each spring under the small cylinders ) or ceramics .. i am puzzled

No, I have no pressure gauge on the system and I am not sure where any opressure valves would be located, at the pump or in the cylinder??

Ok, the pump looks more and more like the issue ... I wonder if they built it that way as we were able to force the helm over, past the HO point, even when the pump was brand new in 2005. Perhaps if you apply enough pressure at the helm it is supposed to protect the system from increasing the pressure too much??? But now, with the pump older and perhaps missing springs it does it too soon ???

I just called Vetus in Holland and spoke with a technician who indicated that when the helm is HO .. if more than 60 Bar of force is applied, then the relief valves in the pump will protect the system by circulating the oil inside the pump. That is a crucial info to know I will now test pump and cylinder individually, then put everything back on our boat with brand new AW 32 hydraulic oil I was very lucky to find in the small town today and then see how it all goes ... Will the helm offer enough resistance when turned HO or will it continue to turn too easily. If the latter was the case, apparently there is not much to be able to do to repair the pump ... so I will have to replace the pump then ... I will keep you posted ...

I was thinking exactly the same thing myself a few days ago ... I guess I wanted to be sure that the system will work in heavy wx and not have the pump bypasssing itself when there is a little more resistance on the rudder ... indeed, if I could connect a pressure gauge to the system, then I would know if it bypasses only when the 50 Bar designed pressure is reach or not!
But, I am not sure how I could do that right now, so I probably will do as you suggest and not worry about it ...

Part of my saga here is that I have a second issue: the autopilot I have now requires 3 turns HO to HO and our actual system has 5 thus rendering the task impossible to the autopilot. I have 3 choices and I can choose the best one ONLY after I determined the problem #1 that is the turning of the wheel past the stop.

To fix the autopilot issue, I can either replace the pump OR the cylinder in order to reduce the numer of turns, OR I could install a hydraulic pump on the autopilot and get rid of the helm wheel connection OR I could get a different autopilot altogether, one that accommodates wheels that turn 5x

After the testing today, I should be able to determine the best way to solve now the autopilot issue ....

We finished testing pump and cylinder today with another pump & cylinder on a friend's boat and we discovered that my cylinder (1980!) is doing very well but my problem is the pump. The relief valve must open at very low pressure.
So I will buy another pump, a bigger one that will give me less than 3 turns HO to HO so my autopilot will be happy with it and both my problems will be solved. I just dread the fitting of the new pump (from a different manufacturer since Vetus has no pumps big enough anyway) as far as connections and housing size ...
Thanks everyone for your ideas ... I will return in a few weeks after I get the pump shipped to me here in the Pghilippines and have finished installing it ... hopefully with a very good ending!