T&T: Air in hydraulic steering caused by autopilot pump

[Phil Keys]

Here's one for the hydraulic experts.

I am trying to diagnose a situation where air gets into my hydraulic 
steering when the autopilot pump is working hard, e.g. in a seaway or 
when crossing tide boils.  The steering gets sloppy until the air is 
worked out by manual steering.

My steering is a 40 year old Wagner system consisting of a T-2 ram 
and dual helm stations with separate lockvalves.  The T-2 ram has 
been rebuilt and the flybridge helm pump and lockvalve were 
disassembled and reassembled.  No problems were found.  I recently 
replaced the old purpose built autopilot pump with a Raymarine Type I 
pumpset.  The pumpset is driven by a Cetreck autopilot control 
computer.  The system is filled with the recommended AWG 32 hydraulic 
fluid.  Besides the pressure lines to the ram, there is a reservoir 
line from the pump through a settling bowl (I think that's what it 
is) up to a tee at the lower helm pump and then up to the flybridge 
helm pump and a small reservoir tank.  This reservoir line was 
recently realigned to avoid dips and to always flow upward.

When working the Raymarine pumpset has made increasing louder 
squawking noises which have lead me to stop using the autopilot.  I 
assume this is due to cavitation.  The pump gets warm but not hot.

I recently increased the autopilot rudder deadband to 1.5 deg. which 
has eliminated constant hunting.  I don't know yet if this has 
eliminated the problem.

Can constant pump operation cause cavitation?   Can this cause air in 
the hydraulic system?  Or can there be another way air gets into the 
system?  I don't find any leaks in the pressure lines.


Phil Keys
Kathy K  Willard 36, hull #34 For Sale
Port Hadlock, WA 98339
philm at keysfamily.org