New Autopilot Pump - does size REALLY matter?

The reversible pump on Smartini is starting to make noises I don't like, and it's 18 years old. I would like to simply replace it. It's a Cetrek unit, with these markings (and nothing else): "Power Pack - PV 4.6 12V". I believe it's this unit: https://maxmarineelectronics.com/pr...pump-pv-4-6-12v-also-furuno-simrad-raymarine/
and I think it's a discontinued product, as I can't find it for sale anywhere.

See the picture.

So now I need a replacement, but I'm finding it difficult. The AP is Raymarine, with their ACU-400 "black box", which works with their two Type 3 pumps, neither of which is big enough to handle the 32.4 cubic inch capacity of the steering ram.

The Octopus OCTAF2012 is advertised to handle up to 30 cubic inches.

The Simrad RPU300 can handle up to 36 cu. in., but their materials say it requires on of the Simrad AP "black boxes". Am I correct in assuming that any brand of "black box" that knows how to control a reversible pump can control this one? (Such as my Raymarine MCU-400?)

Several TF members have said great things about their Octopus pumps. But because their biggest rated one is 6% "smaller" than my ram, should I definitely stay away?

As always, input appreciated, especially anyone who has used the Simrad RPU300 with a non-Simrad "black box".

You can have your pump rebuilt by an electric motor repair shop... Maybe

You can use any reversible pump with an AP blackbox. You need to see if there is a max amperage on the black box and make sure you don't exceed that with the new pump.

To determine the correct pump size to order, you will need to know the displacement of your steering cylinders/rams. Manufacturers will list that on specs.

If you were happy with the performance of the last pump, buy one that is close in size.

Finally, there are variable displacement hydraulic AP pumps available that will allow the correct rudder sweep speed required by some of the new AP's

Looking at your old pump, it looks similar to an AccuSteer variable displacement pump made in Bellingham, WA. You might want to send them a picture of it to see if they can rebuild it.

Most marine electronic companies don't build their own pumps. Most are private label from pump manufacturers.

The Simrad RPU series pumps are simple 2-wire reversing pumps. The control units (black boxes) that drive them reverse the polarity and proportionally the voltage supplied to change direction and steer the boat. Simrad, Raymarine, Comnav, Furuno and others all manufacture similar systems and pumps that are for the most part interchangeable. Just match the pump capacity to the steering cylinder and the pump power requirement to the output from the control unit and typically you will be fine. I've used Simrad autopilots on a number of boats and currently, have a Garmin Reactor autopilot driving a Simrad RPU pump I had as a spare from another boat, and it works perfectly.

All of the systems I am familiar with require a dockside setup or calibration. The control unit will run the pump back and forth to the full extent of the rudder. It measures the rudder angle, time and pump flow and will in most cases correct the voltage to achieve the optimum for the size pump and steering cylinder. I assume the Cetrek system is similar.

I noticed your old pump has a flow adjustment from 0-4.6 liters/min that might have some bearing on your pump selection/substitution. Be sure to note your current setting and compare it to the RPU300's fixed flow of 3.0 liters/min.

Hope this helps.

Thank you both for your replies. I may see if I can have just the motor rebuilt first, and if that solves it, I'm good. However... the sounds that are coming from the unit (kind of a groaning sound each time the rudder is moved more than just a tiny amount) seem more like pump noises than motor noises - but what do I know? Maybe one of you can tell me? Here's a video (more important, the audio) of the sounds I'm concerned about. Motor or pump? Anyone?
https://photos.app.goo.gl/4kNZmm349iiuQtKF7

Tough to say. I think the only thing you can do is take it apart and see what you find. At a minimum the motor should be cleaned out and the brushes replaced. It's probably packed full of brush dust. Any maybe the noise is nothing more than a brush worn down to it's holder.


If you want to go all out, take the motor to an electric motor shop, and the pump to a hydraulic shop.