1. In a hydraulic device including a housing, fluid openings formed in the housing including a high-pressure port, a lowpressure port and a pair of servomotor ports, a bore wall in the housing forming a cylindrical bore communicating with the fluid openings, a cylindrical sleeve valve carried within the bore, means for selectively axially shifting the valve in the bore and complementarily arranged axially spaced circumferential lands and grooves formed of the bore wall and the peripheral wall of the sleeve valve for communicating different ones of the axially spaced grooves with one another as the valve is shifted in opposite directions between first and second positions, a first of said grooves communicating with a second groove in said first position of the valve and serving as a fluid flow passageway and means forming a conduit constantly communicating said first groove with a third groove to pressurize said first groove to reduce parasitic fluid leakage thereacross between axially adjacent grooves in said second position of the valve, the improvement comprising valve means associated with said conduit for blocking fluid flow between said first and third grooves in said one position of said sleeve valve and for establishing relatively free fluid flow with low-pressure loss between said first and third grooves in said second position of said sleeve valve.

6. The method of reducing parasitic leakage between first and second axially spaced circumferentially extending grooves maintained at different fluid pressures and formed in the peripheral wall of a sleeve valve which is shiftable axially between first and second positions and which has formed therein a third groove interposed between the first and second grooves for connecting the first and second grooves in the first position of the valve and for providing a fluid pressure dam between the first and second grooves in the second position of the sleeve valve, comprising the steps of communicating the third groove with a source of a fluid at a higher pressure than the pressure of said first and second grooves when said sleeve valve is shifted to the second position thereof, and completely blocking off the third groove from said fluid source when the sleeve valve is shifted to the first position thereof.

7. Apparatus for reducing parasitic leakage between first and second axially spaced circumferentially extending grooves maintained at different fluid pressures and formed in the peripheral wall of a sleeve valve which is shiftable axially between first and second positions and which has formed therein a third groove interposed between the first and second grooves for connecting the first and second grooves in the first position of the valve and for providing a fluid pressure dam between the first and second grooves in the second position of the sleeve valve, comprising means for communicating the third groove with a source of fluid at a higher pressure than the pressure of said first and second grooves when said sleeve valve is shifted to the second position thereof, and means for completely blocking off the third groove from said fluid source when the sleeve valve is shifted to the first position thereof.

8. A hydraulic manually operated fluid meter-pump device for use in association with a hydraulically operated servomotor comprising a housing having a bore wall forming a cylindrical bore therein and a high-pressure port, a low-pressure port and a paIr of servomotor ports a communicating with said bore, fluid meter-pump means including a pair of relatively rotatable fluid displacement members communicating with said bore, a rotatable shaft connected to said fluid meter-pump means for joint rotation therewith, means forming a series of cooperating lands and grooves in said bore wall and in the peripheral wall of said sleeve valve for controlling the flow of l fluid between said ports and through said fluid displacement means in response to axial movement of said sleeve valve between first and second positions, said grooves comprising, in order, a first pressure groove, a meter groove, a first servomotor groove, a first pressure dam groove, a first return groove, a second pressure dam groove, a second servomotor groove, a second pressure groove, a second return groove and a third pressure groove, first and second conduit means communicating respectively said first pressure groove with said first pressure dam groove and said third pressure groove with said second pressure dam groove, and poppet-type valve means in said first and second conduits for blocking flow in said first conduit and establishing flow in said second conduit in said first position of said sleeve valve and for blocking in said second conduit and establishing flow in said first conduit in said second position of said sleeve valve.