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Description of RPU80/RPU160/RPU300
20220422N 15
3.2 Principle of operation (ref. figure 3-1 and
figure 9-1)
RPU80/160/300 is reversible: that is the motor changes direction
of rotation and the gear pump delivers oil to that side of the
rudder cylinder dictated by the signal from the autopilot. The
pump runs until the signal from the autopilot ceases. The pump
unit has non-return valves on the outlets A and B. When
running, the pressurized (or delivery) side will hold both non-
return valves open, using direct oil pressure upon the valve on
the delivery side. This oil pressure is also used to push a slide to
open the valve on the suction side.
When the motor stops, the spring (8) in the non-return valve on
the suction side returns the slide to the neutral position. Both
non-return valves are now closed and the rudder cylinder
locked. Both sides of the gear pump have suction valves to
outlet C.
If the rudder cylinder is loaded in the same direction as the
rudder command, the slide (10) precisely positions the non-
return valve (suction side) such that the creation of a vacuum in
the rudder cylinder is prevented. (A vacuum in the rudder
cylinder would result in air being drawn past the seals round the
cylinder piston rod, since these stops the oil pressure only). At
that side of the valve block where the motor is connected, there
is mounted sealing ring (15) and support ring (16) in the valve
block. The support ring causes that the tank connection C can
hold a maximum pressure of 7 bar (Ref. Hynautic steering
systems).
Note !
1. A previous model of RPU80 Reversible Pump was simplified
according to the principle diagram. (Ref. figure 3-1 and
figure 9-2). The principle of operation was similar to that of
RPU160. The (suction) valves, however, operated as
combined suction and non-return (check) valves controlled
by internal pressure and direction of oil flow. The resulting
effect was a smoother non-return (check valve) function as
compared to the one with separate non-return valves.
2. It should be observed however, that the previous model of
RPU80 does not have the extra protection against internal
leakage (bypass) as the other models with separate check
valves.
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