Vague Hydraulic Steering after fluid leak

[telewis]

Sealine S38 with 2*260HP Volvo D4 and DHP Legs. Single Helm. Raymarine Autopilot

Two seasons ago I noticed hydraulic fluid in the marina. On lifting, I found a leak of emulsified hydraulic fluid leaking from one of the steering rams. This was replaced as part of the service. Every since, the steering has felt vague as if there was a large amount of free play in the system. Over time, it seems to be getting worse. Engineer thinks it is fine but he has only seen in marina at low speed. Having almost hit the lock in Hythe at the weekend, very grateful for any advice.

Number of observations if helpful. It is less responsive to port than it is to starboard. Agressive helm movements seems to generate more response than slower ones. Autopilot is also struggling causing boat to veer from side to side quite harshly. When disengaging autohelm, steering seems to sometimes not reengage; putting autopilot back on and off can resolve (it there is a value somewhere?). Turning wheel with engines off (or reaching full lock) causes wheel to move in jumps and starts - as if it pushes and then leaks the pressure.

Really grateful for any advice please

 

[superheat6k]

Do you have bleed nipples on the ram ? I would also check for sags in the piping from the steering, as this can allow air locks to form.

A simple fitting at the upper helm fill point to keep the helm pump completely full, then wind the wheel over hard lock to hard lock. Also spin the wheel against the autohelm. I would also bleed large volumes of fluid from any nipples via a clear tube immersed in a jug of fluid.

Whilst doing this physically lift any sags to allow trapped air to rise to the header tank. Basically got to get the air out and not let more in during the process. I am not sure the 'engineer' concerned would be happy with the brakes on his car being left like your steering !

 

[spannerman]

Souns like the system wasn't bled properly, the easiest way is at the helm, first the lower then the upper if flybridge.
It involves a lot of wheel twirling with the engine with the servo pump running as this makes it easier. Also run autopilot pump both ways, eventually it will stop bubbling air at the helm steering pump and the level will stabilise. If it doesn't work after this either another ram has started to leak or the shuttle valve at the back of the engine has been damaged if the oil has been contaminated with seawater, the oil in the servo reservoir should look like thick Ribena (ATF) if it is pinkish then there is water in it which means a complete flush of the system and any defective parts replaced.

 

[NormanS]

If your system is fitted with a manual bypass valve, which is normally fitted so that emergency steering can be used, open this valve and keep turning the steering wheel(s), to chase any air out of the pipework. You will find this much easier than trying to lift pipes.
Your rams should have bleed screws, which lets you get any air out of them.

 

[telewis]

NormanS / Spannerman / Superheat6k - Very helpful - thank you.

Only remaining question is whether I should bleed with engines on or off. If on, will it push fluid out of the helm under pressure.

Many thanks

 

[spannerman]

There are NO bleed nipples on a Volvo D4/6 setup, the air works its way out to the highest point, it is a low pressure system from the helm pump controlling a valve which allows the high pressure servo assisted side to help you so I would do it with the engine running as its heavy on the steering without the servo pump a bit like on a car.
There is no pressure on the return side to speak of, its only the same as what you push down the lines by hand when you turn the wheel, what will happen is air will bubble out bringing oil With it so have plenty of rags ready, I have a plastic tube which screws into the resevoir going to a 1 1/2 ltr coke bottle so the air/oil bubbles up into the bottle instead of going all over the dashboard. All the high pressure bit is Down in the engine room and goes to its own reservoir.

 

[telewis]

There are NO bleed nipples on a Volvo D4/6 setup, the air works its way out to the highest point, it is a low pressure system from the helm pump controlling a valve which allows the high pressure servo assisted side to help you so I would do it with the engine running as its heavy on the steering without the servo pump a bit like on a car.
There is no pressure on the return side to speak of, its only the same as what you push down the lines by hand when you turn the wheel, what will happen is air will bubble out bringing oil With it so have plenty of rags ready, I have a plastic tube which screws into the resevoir going to a 1 1/2 ltr coke bottle so the air/oil bubbles up into the bottle instead of going all over the dashboard. All the high pressure bit is Down in the engine room and goes to its own reservoir.

Magic. A Coke bottle it is then! Thank you