Hydraulic motor with adjustable flow volume

An adjustable, axial or radial piston type hydraulic motor having at least two cylinders and pistons cooperating with a rotary crankshaft or with a reaction guiding member, a fluid flow distributor, intake and return pressure conduits provided between the distributor and the cylinders, comprising at least one pressure-actuated control valve arranged in one of said pressure conduits, said control valve being a check valve spring-biased into its closing position by a relatively weak biasing means, said check valve being formed with a first surface portion exposed in its opening direction to pressure fluid from said cylinder, a second surface portion exposable to pressure fluid either in opening direction or in closing direction depending on the relative position of said distributor to the pressure conduit for the check valve, and a third surface portion exposable to working fluid in opening direction;

• said second surface portion being at least as large as said first surface portion and larger than said third surface portion, and the combined areas of said first and third surface portions being larger than the area of said second surface portion.