Hydraulic steering fault

[EuanMcKenzie]

Got a problem with my hydraulic steering on my old HR Rasmus.

Toward the end of last season we experienced slippage at the wheel and had to keep winding it to keep the boat on course in the gusts.

Its a simple system, Vetus pump at one end and cylinder at the other and there is also an autopilot steering pump in the circuit.

I have stripped the steering pump for inspection. It is a five piston unit and surprised me as there are very few gaskets and seals involved. Everything seems to rely on close machined fits for the pistons etc.

It was all functional so the conclusion I have come to is that it is either fine and I need to strip the cylinder next or else the tolerances are worn and its new steering pump time.

Has anyone had similar problems and how did they get round it. I don't want to spend a fortune on what looks like rather old kit but on the other hand the pump fits the tabernacle and a replacement will need work to make it fit

I have lots and questions in my own mind and want to know what to do next? Has any one had similar issues and how did you resolve them.

Does anyone know a company in / around scotland west coast or else where that can overhaul these components?

Is it worth it or do I get the VETUS catalogue out and start again. I reckon the bits will be circa £500. Putting the old bits back is easier on the install than new bits so I have to take that into account but also weigh it against long term reliability.

Any thoughts & Advice?

 

[Bilgediver]

Got a problem with my hydraulic steering on my old HR Rasmus.

Toward the end of last season we experienced slippage at the wheel and had to keep winding it to keep the boat on course in the gusts.

Its a simple system, Vetus pump at one end and cylinder at the other and there is also an autopilot steering pump in the circuit.

I have stripped the steering pump for inspection. It is a five piston unit and surprised me as there are very few gaskets and seals involved. Everything seems to rely on close machined fits for the pistons etc.

It was all functional so the conclusion I have come to is that it is either fine and I need to strip the cylinder next or else the tolerances are worn and its new steering pump time.

Has anyone had similar problems and how did they get round it. I don't want to spend a fortune on what looks like rather old kit but on the other hand the pump fits the tabernacle and a replacement will need work to make it fit

I have lots and questions in my own mind and want to know what to do next? Has any one had similar issues and how did you resolve them.

Does anyone know a company in / around scotland west coast or else where that can overhaul these components?

Is it worth it or do I get the VETUS catalogue out and start again. I reckon the bits will be circa £500. Putting the old bits back is easier on the install than new bits so I have to take that into account but also weigh it against long term reliability.

Any thoughts & Advice?

Double check the pipe circuit to see how the auto pilot pump has been installed . Is it just in parallel with the manual steering pump or is there also a shut off valve in the auto system. The leakage could well be in the auto system when using manual. Does the auto pump rotate when applying helm manually?

 

[PaulJS]

Bilgediver's suggestion sounds the most likely culprit, but it is definitely worth investigating further before buying new components as hydraulic systems tend to be very reliable so long as there is no contamination.
If the steering pump is ok the oil must be circulating past either the ram seals or through the autopilot pump, and all it takes is one small piece of swarf or grit to damage a seal...
Is there a relief valve anywhere in the system that might be passing?

Good luck!

 

[Deleted member 36384]

Squash Plates and Pressure Control Valves

.......Is there a relief valve anywhere in the system that might be passing......

Indeed, a relief valve could be the culprit, however on many types of hydraulic pumps there are pressure control valves built into the discharge end of the pumps. They can be as simple as a spring and a ball seat or quite complex controllers. However, it is not likely to be complex on your pump.

Their purpose is to dump excess pressure or maintain output pressure at a factory setting and are not actually over pressure protection devices, just part of the pump set up.

Anyway, look for such a device in the pump on the output as it could be venting pressure below its set point as rudder pressure indirectly causes the valve to lift.

I really don't know how your pump works but if it has a squash plate then that plate maybe out of alignment or the devices that push the pump pistons. As the boats wheel turns the squash plate (think of a cam shaft) pushes the pistons in (or allows them to move back) thus controlling hydraulic fluid displacement into the rudder circuit. On some pumps the angle of this plate is adjustable, so if there is something wrong with this device, then under pressure it may creep allowing the pistons to travel back and thus requiring more fluid to maintain rudder angle.


Of course as you state it may be the steering rod passing. School Hill Hydraulics in Aberdeen, www.schoolhillengineering.com, are good with all sorts of small and big hydraulics. They might have grown too big now to be interested in small stuff but I know them as a very helpful firm.

 

[EuanMcKenzie]

re comments

I think autopilot pump is in series with circuit but i will check next time i am at the boat. The system is broken anyway. There is no bypass.

The boat is out of the water and when you push the rudder the wheel turns both ways.

The pump has 5 cylinders which arr located in a rotating carriage driven by the. There is a fixed plate on a roller bearing placed at an angle and this pushes the pistons in as the carriage is rotated.

The pistons have a spring inside that pushes them back out again. There is a ball bearing valve in the end of the piston to allow oil inside the piston. This should seal up when the piston drives

There is no relief valve but the whole pump chamber has a header tank above and that sets the level. It doesn't move or bubble in use. The pump is fed on one side from the return circuit while it delivers to the drive circuit on the rudder piston.

I think the next move may be to drain the system, reseal the rudder piston, bypass the autopilot with some valves, refill it all and see where I'm at. If that doesn't work then its the steering pump i think. I still like to repair rather than replace it if I can - part of the engineer in me!

Only question i still have nagging is, if the ball bearings valves or pistons are passing in the steering pump, what can i do about it? The pistons are a machined fit and are numbered to
ensure correct assembly.

Are the ball valves a likely cause and are they repairable?

I know these items are reliable generally but the boat is a 1972 and the system looks original so it could be wear and tear.

Thanks for your comments so far, the problem is obviously fixable one way or another

Euan

 

[Bilgediver]

I think autopilot pump is in series with circuit but i will check next time i am at the boat. The system is broken anyway. There is no bypass.

The boat is out of the water and when you push the rudder the wheel turns both ways.

The pump has 5 cylinders which arr located in a rotating carriage driven by the. There is a fixed plate on a roller bearing placed at an angle and this pushes the pistons in as the carriage is rotated.

The pistons have a spring inside that pushes them back out again. There is a ball bearing valve in the end of the piston to allow oil inside the piston. This should seal up when the piston drives

There is no relief valve but the whole pump chamber has a header tank above and that sets the level. It doesn't move or bubble in use. The pump is fed on one side from the return circuit while it delivers to the drive circuit on the rudder piston.

I think the next move may be to drain the system, reseal the rudder piston, bypass the autopilot with some valves, refill it all and see where I'm at. If that doesn't work then its the steering pump i think. I still like to repair rather than replace it if I can - part of the engineer in me!

Only question i still have nagging is, if the ball bearings valves or pistons are passing in the steering pump, what can i do about it? The pistons are a machined fit and are numbered to
ensure correct assembly.

Are the ball valves a likely cause and are they repairable?

I know these items are reliable generally but the boat is a 1972 and the system looks original so it could be wear and tear.

Thanks for your comments so far, the problem is obviously fixable one way or another

Euan

If the steering cylinder is a SINGLE cylinder which sits in mid positiion for straight ahead and then strokes one way for port and the other for starboard then it is possible that the piston seals have worn out and you are getting leakage past the piston. This is easily checked by disconnecting one of the cylinder connections IE the one for giving port helm with the rudder in full starboard position and putting the hose end to the helm in a container of oil.. Then apply starboard helm. The piston can not move as it is already at full helm however if the piston is leaking then oil will come out of the cylinder connection as the wheel is turned. This oil will have leaked past the piston. If no oil leaking and helm is slowly turning then have to look elsewhere.

 

[NormanS]

Quote:
The boat is out of the water and when you push the rudder the wheel turns both ways.
end quote.

This is very unusual with a hydraulic steering system. Usually there is no feedback to the wheel from the rudder. It suggests that the cylinder is OK, but there is something strange going on in the pump. A swashplate pump, which is as you describe, should not be able to be rotated by pressure coming back.

 

[Bilgediver]

Quote:
The boat is out of the water and when you push the rudder the wheel turns both ways.
end quote.

This is very unusual with a hydraulic steering system. Usually there is no feedback to the wheel from the rudder. It suggests that the cylinder is OK, but there is something strange going on in the pump. A swashplate pump, which is as you describe, should not be able to be rotated by pressure coming back.

In actual fact a swash plate pump can be used as a swash plate motor this is why the helm returns on these boats under the influence of water pressure on the rudder.

http://www.boschrexroth.com/country...products_ss/05_motors/03_swashplate/index.jsp

 

[NormanS]

In actual fact a swash plate pump can be used as a swash plate motor this is why the helm returns on these boats under the influence of water pressure on the rudder.

http://www.boschrexroth.com/country...products_ss/05_motors/03_swashplate/index.jsp

I stand corrected, but I have owned one, and handled a great many boats with hydraulic steering, and without exception, the helm could be put over and left, and the boat would continue in a circle, without any tendency to straighten up. This is actually one of the great benefits of hydraulic steering. I suggest that swashplate motors have their plates at a greater angle than those on pumps normally used for steering.

 

[hightech]

All the pilot pumps I have ever come across cannot pass fluid from one side to the other by virtue of the way they are made, generally a gear pump which cannot be back driven in normal usage. So it is unlikely to be there. Some do have a pressure relief valves which will vent from a feed line to the return line, you can easily see if this is the case by turning the wheel while the return pipe is monitored for any flow. Normally the return line is only there for the pilot pump and plays no part in the standard steering.

Moving then to the steering, for a pilot pump to work, the steering must not be able to be back driven, i.e. pushing the rudder should not turn the wheel. Otherwise when the pilot pump runs, the same thing will happen i.e. the wheel will turn and the rudder will stay still. So, has the check valve in the steering pump failed? Generally Vetus pumps do have inbuilt check valves. If you have stripped the pumps, you may have disturbed the settings or reassembeld incorrectly.

Steering cylinders generally fail in one of two ways. 1. The piston will normally have a central portion which is sometimes attached to the through rod by a roll pin, this roll pin can fail and the rod then moves free,if this happens you would have lost steering completely, so probably not likely. 2. The seals on the piston ends failand oil leaks out, very obvious to see.

My opinion is that your helm pump has failed and needs replacing/rebuild (properly).

 

[DownWest]

Why not disconnect the hoses at the ram and plug them. If the wheel still turns, isolate the A/P pump. If that doesn't stop the wheel, then it is probably in the helm pump.
My only (boat)experience was on a single ram with A/P and two helm positions (same type of swash plate pumps) The seals on the ram failed, leaking oil into the bilge. So the cure was pretty obvious.
Personally I would look hard at the A/P system and the ram. As said above, hydraulics are very reliable if kept clean. It is the interface with air that usually causes problems.
A

I did not see Geoff's post before this. As it is in bits at the moment, why not reassemble it and try it with plugs in the outlets, any internal leakage would be obvious. I still think looking further aft might result in solving it

 

[impact30]

Had this during the year with my wagner system. Had all the thoughts you are having about the trouble and expense and wether a new system would be best.
At the hard over position the leakage, while still there, was considerably less.
Jam the cylinder with something (I used a socket) with the rudder in mid position or thereabouts and check again. If leakage is more then it is certainly bypassing the seals in the cylinder.
Seals for mine were easily available locally in the West of Ireland and were a doddle to fit.
My old ones were compound seals and came out in pieces, hard to imagine how they worked at all.
New ones were just simple rubbery plastic affairs (€2 ea )and when reassembled steering was better than new. Bleeding is a pain though.
Not a job to be afraid of at all.
Good luck
Padraic

 

[EuanMcKenzie]

re pump

Thanks for all your comments. If there is a non return valve in the outlet I can't see it.

Its a single wheel pump and piston so i don't think you need them. The same line feeds and returns from the cylinder as you turn the wheel one way then back again so i don't know how they would work

The non return bit is in the head of the Piston so it can draw additional oil into the circuit. I will try to post some photos to make it clearer if I can work out the technology of how to do it.

I am going up to the boat during the week to have a go. Will plug things etc and let you know my findings. Found some well priced bits here so this will be my plan B

www.leisureshopdirect.com/marine/ou...mps_and_accessories/Vetus_Steering_Pumps.aspx

has anyone dealt with these guys?

 

[EuanMcKenzie]

Update

Vetus have identified the parts from photos and confirmed that they are original and approx 35 years old, which would approximately align with the boat build age 1972. That said we think it is the cylinder

I have removed both from the boat and will set them up in the garage to prove them one way or another.

Also, the cetrek hydraulic pump is in parallel with the wheel circuit so I have taken it out just now. I will add isolation valves when i reinstall in case it is a continued problem.

I plan to try and find seals off the net somewhere and see If I can get the cylinder to work. If not Vetus have a direct replacement which I will buy.

Again the steering pump cylinders have no replaceable seals so if its passing then its a replacement again. I want to avoid this as it will mean lots of butchery to the pedestal.

What was surprising is that the parts are not that expensive < £500 the pair so it may be the way to go

I guess this year is turning into a lots of work year!



Euan

 

[Bodach na mara]

I will be watching this thread with interest as my own hydraulic system has had a tendency to do its own thing occasionally since it was new. It is also a Vetus system but without the autopilot pump. There is also no reservoir for the fluid except the pump itself. I would love to talk to someone who can explain just how "non-return" valves work in such a system.

I applaud your ability in dismantling the pump. I am much too feart!

 

[rogerthebodger]

"I would love to talk to someone who can explain just how "non-return" valves work in such a system."

I will try

The type of non return valve is in fact a "pilot operated non return valve" http://www.srentpindia.com/Pilot operated NRV.pdf

It is a special type that will allow flow only one way but has a pilot inlet that can open the valve so to allow flow in the normal non flow direction.

With the hydralic steering on a boat with a pump and cylinder if there is only one steering position the pump does not need a pilot NRV and you will get feed back from the rudder.

If you have more than one steering position and that includes the auto pilpt pump, each steering pump must have a pilot NRV on the outlets of all the pumps. The pilots on each pump is cross linkes to the opersite pump port. This means that when a steering pump is turned oil will flow out of one port past the NRV in the normal flow position and back into the pump at the other port but as it has a NRV fitted no flow would take place but with the pilot cross connected to the outlet port this would cause the inlet NRV to open thus allowing flow.

The second steering pump would have both it pilot NRV closed so no flow would pass through that pump and all oil would go the the cylinder.

Vetus do both kinds of pump but also do an external valve block that will act in the same way.

On my boat I have and inside and outside steering positions plus an auto pilot pump so all the pumps have pilot operated non return valves.

If these valves were not fitted in a multi steering setup the tendiency would be for the non operated pump to turn when the operated pump was turned so the oil would bypass the cylinder and the rudder would not turn.

Hope this helps

 

[Bilgediver]

Vetus do both kinds of pump but also do an external valve block that will act in the same way.

Hope this helps

I suspected that the non return valves had some sort of lock out facility however my favourite is the valve block.

I suspect in the OP s case either the cylinders piston seal was leaking and or the oil was leaking through the aotohelm pump when on hand. The Cetrex needs to be checked to see if it has a pilot operated NRV and if fitted is it working. Do these valves need the helm neutralised before changing modes to ensure the PilotNRV closes?

 

[Bodach na mara]

Thanks Roger, it helps a bit but I will need to get it down as a diagram before I can really get to grips with it. I did realise that some sort of return path was needed but could not see how this would not "short-circuit" the system and remove any driving force. From the info supplied by the OP, I suspected that a pump malfunction mat be the cause of his problems and now think that the internal NRVs may be leaking.

 

[rogerthebodger]

I have been looking for a schematic for a typical steering pump but not found one yet but below is a sectioned drawing of one on my pumps which may help.

The PNRV is shown on the end view with item 14 as the pilot lock spool which opens the inflow PNRV.

 

[Bodach na mara]

Having now read all th OP's posts in the thread, I think the pump is a radial piston pump. What puzzles me is that the pump is reversible and all the diagrams I have found have been for one-way pumps in which the same outlet port is fed no matter which way the pump turns. I assume that there is some sort of two-port system to ensure hat wehn the pump is turned clockwise the fluid is directed out of one port and returns by the other and vice versa for anti-clockwise. It definately seems like a short-circuit within the pump.

For what it is worth, my own system has no header tank (none needed say Vetus) and in the first year I did not realise that there was some leakage. I had the symptoms described when crossing Rothesay bay and could only steer to berth in the harbour by winding the pump continuously. When I checked, there was no fluid showing in the pump and on refilling and bleeding, normal operation was resumed. I now check fluid levels more regularly. I am not suggesting that the problem here is as simple, but it does seem that the pump is not developing pressure.

Finally, there IS feedback in the system. Not that it is noticable when steering, but when the boat is out of the water, if the rudder is turned by hand (eg when antifouling) then the wheel spins in the cockpit. And a final final point. Consider an agricultural engineer for repair. They service these things on tractors all the time.