(57) An hydraulic control system, particularly for controlling the movements about two
axes of the nozzle of a fire fighting monitor. The supplies of working fluid, preferably
water, from a source 18 to two double-acting actuators 58, 9 provided for. this purpose
are controlled by four pilot operated control valves 13-16 fed with hydraulic pressures
signals, transmitted through a different fluid, from a remote hand-operated pressure
generator23. The transmission of signal pressures to the control valves may be effected
via long lengths of flexible plastics tubing 27A-27D filled with the signal fluid
and in order to avoid problems with the propagation of pressure changes through such
tubing due to its inherent elasticity, the range of signal pressures to which each
control valve is adapted to respond is selected to be at a relatively high level as
compared with the pressure of the working fluid.
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