Boat Forum / Building / June 2006

Larry,
All helm pump manufacturers equip their helm pumps with non-return valves if
there is additional helm stations and/or an autopilot pump. So, this is the
norm, not the unusual. You would not want the steering wheel to rotate
rather than the rudder move when in autopilot mode. Nor would you want the
wheel on the flybridge to turn the wheel in the wheelhouse rather than the
rudder. That is what they are used for, but they have a secondary effect as
well and that is to prevent the rudder acting like a pump and kicking the
wheel. On sailboats, rudder feedback is a great tool in trimming the sail
plan for rig balance, so you would then want a manual valve where you can
turn on the feature with a lever if in rough water or when using an
autopilot. This is not rocket science. It is common sense. The double pilot
bit is that the non-return capability must be on both of the oil ports of
the pump because either side could be IN and OUT, depending on wheel
rotation.
Steve

We just had to have a pilot operated check valve replaced on our back hoe.
On the back hoe we have singles and doubles.  The single holds the bucket in
position until the pump pressure tells the valve to open and move the
bucket.  The double is in the steering circuit to prevent the steering wheel
from jumping when the front wheels hit an obstruction.

What it does is act like a regular check valve until it sees pressure on the
pilot port and then turns it into a two way valve.  On a double the pressure
lines from opposite sides are piped to the pilot ports so that when the
starboard valve sees  pressure from the port steering side it opens and lets
the hydraulic fluid flow back to the pump allowing normal steering.  If the
rudder is jammed over to port pressure on the starboard line to the rudder
will be high and pressure from the port pump to its check valve will be low
so the starboard check valve closes and prevents back flow to the pump.

The 211-1009 is just an open center control and does not come with check
valves.   Open center controls direct the output of a constant pressure pump
and high pressure back flow can not only jerk the wheel but also damage the
pump leaving you with no steering at all.  Normally you would probably use a
relief manifold that has the check valves built in.   The relief manifold
bleeds the excess pressure back to the pump reservoir but that would let the
rudder move a little on its own and I am not sure you want that to happen at
120 MPH.

Eaton and Parker both make pilot operated check valves.  You might check
their catalogs for a double.  Worse case you could get two singles and tap
off the ports of the 1009 to cross feed the pilots on each valve.