referring to the drawing figures and in particular to fig1 and 2 , the preferred embodiment hydraulic piston 7 is disclosed . the hydraulic piston 7 is provided with an axial opening 30 into which a piston rod ( not shown ) is receivable . edge 32 of piston 7 is provided with channel 31 into which a sealing ring 33 ( see fig3 ) may be received . the hydraulic piston 7 is provided with a bore 10 therethrough which is axially parallel to the axis of the piston 7 and is spaced apart therefrom . counterbores 6 and 16 are made on the opposing faces 21 , 22 of the piston 7 , the counterbores 6 and 16 being coaxial with the bore 10 through the piston 7 and of a fixed depth . a valve spool 12 of cylindrical configuration is receivable within the bore 10 of the piston 7 in a close fit yet slidable therewithin . the valve spool 12 is provided with an internal axial passageway 4 and with at least two radial ports 3 along the length of the spool 12 , the ports 3 being communicative with the internal passageway 4 of the valve spool 12 . the ports 3 are positioned such that they are generally symmetrically located along the valve spool 12 and spaced apart somewhat more than the length of the bore 10 between the counterbores 6 and 16 . each port is immediately adjacent to a stop member 2 or 2 &# 39 ;. in the preferred embodiment , ports 3 are formed by cross drilling the valve spool 12 resulting in pairs of diagonally opposed paired ports 3 near the ends of valve spool 12 . the valve spool 12 is provided with stops 2 and 2 &# 39 ; which are suitably fixed to the valve spool 12 and which serve to enclose the ends of the axial bore 4 through the valve spool 12 . in the preferred embodiment , stop members 2 and 2 &# 39 ; are retained to spool 12 by threaded shaft 30 . each of stop members 2 and 2 &# 39 ; is cylindrical in shape and is sized such that each will freely fit within the counterbores 6 and 16 on the faces 21 and 22 of the piston 7 . when stop 2 &# 39 ; is fully received in counterbore 6 , the inner face 5 of stop 2 &# 39 ; will abut seat 9 of counterbore 6 . stop 2 is identically receivable in counterbore 16 upon seat 19 therein . the radial ports 3 of the valve spool 12 are disposed along valve spool 12 such that when one stop 2 &# 39 ; of the valve 1 is abutted with the seat 9 of counterbore 6 of first face 21 of piston 7 , the port 3 nearest the abutting stop 2 &# 39 ; will be within the bore 10 through the piston 7 , while the port 3 on the opposing end of the valve spool 12 will be in communication with the counterbore 16 of the other face of the piston 7 . counterbores 6 and 16 serve as hydraulic dash pots for stop members 2 &# 39 ; and 2 respectively when either is urged toward bore 10 . stop members 2 and 2 &# 39 ; act like poppet valves in their interaction with counterbores 16 and 6 , each preventing working fluid from passing through bore 10 when the stop member is fully seated in its respective counterbore . the presence of working fluid in counterbores 6 and 16 allows for a cushioning of stops 2 and 2 &# 39 ; when they seat in the counterbores 6 and 16 . referring to fig3 , and 5 in particular , operation of the valve may be visualized . when working fluid is applied to the first face 21 of the hydraulic piston , the working fluid forces the relief valve 1 along the bore 10 through the piston 7 to a first state where the stop 2 of the relief valve 1 abuts the seat 9 of the counterbore 6 on the first face 21 of the piston 7 . as the piston 7 approaches the end cap 24 of the cylinder , the stop 2 on the first end 14 of the valve spool 12 which protrudes from the second face 22 of the piston 7 engages the end cap 24 of the cylinder 25 and is urged through the bore 10 of the piston 7 toward the trailing first face 21 of the piston 7 . as the valve spool 12 slides through the bore 10 toward the first face 21 of the piston 7 into an intermediate position , the radial ports 3 of the valve spool 12 reach alignment ( see fig4 ) with the counterbore 6 and 16 on faces 21 and 22 respectively , of the piston 7 , and a passageway is created from the counterbore 6 on the first face 21 of the piston 7 through the radial port 3 on the valve spool 12 nearest the first face 21 of the piston 7 through the internal bore 4 of the valve spool 12 and through the radial port 3 on the first end 14 of the valve spool 12 into the counterbore 16 on the second face 22 of the piston 7 . when the passageway is so created , working fluid is allowed to pass from the first face 21 of the piston 7 , in the direction of arrows b , to the second face 22 , thereby reducing pressure on the first face 21 of the piston 7 . when working fluid is directed to the cylinder 25 to reverse the movement of the piston 7 into an extend stroke , the roles of the leading and trailing faces of the piston 7 reverse . pressure of the working fluid causes the relief valve 1 to rapidly slide from its position abutting the end cap 24 of the cylinder 25 into a second state where the valve 1 in engagement with the pressurized working fluid is urged into the bore 10 through the piston 7 until the stop 2 on first end 14 abuts the seat 19 within the counterbore 16 on the second face 22 of the piston 7 which has become the trailing face of the piston 7 . when the valve 1 is so positioned , no passageway is provided through the valve 1 or the bore 10 in the piston 7 and the piston 7 is urged toward the head gland ( not shown ) opposing the end cap of the cylinder 25 . as the piston 7 approaches the head gland , the end of the valve 1 protruding from the advancing first face 21 of the piston 7 engages the head gland of the cylinder 25 and is forced rearward relative to the piston &# 39 ; s advance , to the intermediate position where the passageway through the bore 10 of the piston 7 by way of the internal bore 4 of the valve 1 is established and working fluid may pass to the first side of the piston 7 to reduce the pressure and avoid stress on the head gland . it is found that the disclosed design requires far simpler machining operations than that required for prior art valve structures , and that heat build up and premature failure are avoided . it is also found that the stop 2 to seat 9 abutment creates a tight seat for the valve 1 and that cushioning by residually present working fluid is provided as the stop 2 &# 39 ; and seat 9 of counterbore 6 engage . the same dash pot function is similarly provided by stop 2 and seat 19 in counterbore 16 . it is to be understood that in the preferred embodiment of the valve 1 shown in fig1 and 2 , the valve spool 12 is provided with diametrically opposing radial ports 3 . the use of opposing ports simplifies the machining of the valve spool 12 and alleviates stresses between the bore 10 and the valve spool 12 . in fig3 , and 5 it can be seen that the stops 2 and 2 &# 39 ; of the valve 1 may be retained by use of a central stud 30 which passes through internal bore 4 of valve spool 12 and retains stops 2 , and 2 &# 39 ; by screw threading or other securing means .