Low noise hydraulic servo valve

Claim 1

A valve for controlling the flow of fluid from a source of fluid under pressure to a load and from said load to a return, including a valve body formed to define an interior chamber having ports communicating with said chamber for connection to said source, to said return and to first and second load conduits and including a valve spool having lands positioned relative to each other and to said ports so as to define a neutral position at which the flow of fluid from said source to said load and from said load to said return is blocked and also positioned so that upon displacement of said spool from said neutral position flow of fluid from said source to said load and from said load to said return is initiated in a sense and an amount determined by the direction and magnitude of such displacement, characterized in that said lands and said ports are also relatively positioned and said ports are adapted to be connected to said source, said return and said first and second load conduits so that, when connected, pressure differentials are established such that through any one port fluid tends to flow in but one direction, never tending to flow in the reverse direction and so that in said neutral position said lands block only those ports through which fluid tends to flow in the direction from said chamber to said ports, while displacement from said neutral position variably unblocks selected ones of said same ports as said spool is displaced in one or the other direction, leaving completely unblocked for all operative positions of said spool those ports across which the pressure differentials are such that fluid tends to flow from said ports into said chamber, and further characterized in that a restrictor matrix is included in each of those ports which is blocked by a land when said spool is in said neutral position, each of said restrictor matrices comprising a plurality of plates, each formed with a central bore having a diameter to form a sliding fit with said lands, and each formed with a plurality of raised baffles on one side thereof, said plates being positioned coaxially to form a stack having a central bore and defining a plurality of restrictive passages between each pair of adjacent plates for the passage of fluid radially outwardly.