T&T: Can an autopilot pump's output rate be throttled?

[Phil Keys]

Hello all you autopilot experts.

Kathy K has a problem with air getting into the hydraulic steering 
when the autopilot has to work hard.  It then takes many turns of the 
wheel to work out the air.  The steering is OK when the autopilot 
isn't used.  The Wagner T-2 steering ram has been rebuilt so now I 
suspect the old autopilot belt driven pump (40 years old?).  I am 
trying to determine the correct size replacement pump.  The pump 
motor is controlled by a Cetrek autopilot computer.

I have read that the time for hard over in one direction to hard over 
in the other direction should be 10-15 seconds.  The ram's 
displacement is 9.9 cu. in. which translates to a pump rate of 40 to 
60 cu. in./minute.  There are a number of Raymarine Type 1 pumpsets 
on eBay which have a flow rate of 67 cu. in./min.  This gives a hard 
over to hard over time of 9 seconds which seems a bit quick.

So the question is, can I use a valve on the pump output to either 
throttle the flow rate or bypass some of it?  Or should I try to 
adjust the Cetrek controller to compensate for a faster flow 
rate?  Or should I look for a slower pump?

I think the autopilot computer drives the pump motor at a constant 
rate rather than at a variable rate.  When the autopilot is working 
the pump is constantly turning back and forth in short bursts.

I could keep the old 12 vdc motor, hydraulic manifold with the 
pressure relief valves and external lock valve and just replace the 
built driven hydraulic pump but I think a modern pumpset combines all 
of those into one unit.  I know the displacement of the old pump but 
I don't know the motor's rpm.  It looks pretty slow.


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