On my boat, the original hydraulic system had an on demand Monarch
hydraulic power unit that supplied pressure at about 2200
psig to five hydraulic functions, four of which were small
hydraulic cylinders for control surfaces and the drop weight and one
hydraulic motor connected to a lead screw that moves a 100 lb trim
weight for longitudinal trim. All fly by wire through a joy stick
connected to my PLC. I used
electrohydraulic
cartridge valves for pressure and flow control from
www.hydraforce.com Lessons
learned. All systems worked as designed but the HPU I was using
was very noisy and consumed way to much power. Both bad for a
small electric psub. I am currently installing version two of my
hydraulic system. I have dumped the central HPU and cartridge
valves I am now using four small quite
independent pumps/motors that are used on sail boats for autopilot
http://www.accu-steer.com/HRPSeries.html These
pumps put up about 1100 psig and coan run on 12 or 24 vdc. I have
connected one of these small pumps for each control function
i.e., yaw, roll, pitch and trim hydraulic cylinders/motors.
The speed of these small hydraulic pump/motors is controlled by
PWM driver cards
http://www.dimensionengineering.com/Sabertooth2X25.htm.
Each of these cards control two pump/motors so I have two. My
dual axis joy stick sends a 0-5vdc signal to PLC for pitch and roll
movement. My rudder pedals are connected to a pot that is
connected to the PLC. The PLC has a analog input module to receive
these control signals. The PLC also has a Analog output module
that sends the 0-5 vdc output signals to the pump/motors where 0
vdc is full speed one direction, 5 vdc is full speed in the opposite
direction and 2.5 vdc is full stop. When I get the boat back in the
water, I will see how new hydraulic system works but just from bench
testing, I can see that the new system pulls way less power and is very
quite. The nice part about running the control functions through a
PLC is that it is easy to setup an autopilot system in the future
that will hold the boat heading / depth / speed.