A mixing head for mutually reactive components, e.g. of a synthetic resin to be injected into a mold cavity, comprisess a control member which is shiftable in a mixing chamber opening into the mold cavity between a position in which mixing of the components can occur in this chamber and a position in which the member expels the mixture from the chamber and provides recirculating passages for the two components. A displacement body can be inserted into the chamber to control the mixing action by a fluid-operated actuator hydraulically coupled to a fluid displacement member shifted by the control member.

A load control device applicable on agricultural machinery in general and in particular on machinery used for direct planting, so that the working components in contact with the ground will maintain the same load constantly at all times for any ground profile condition. An oil-pneumatic device is provided with a fluid compressor connectable to the tractor's power take-off by a cardan shaft and an electromagnetic clutch that can be powered from the tractor's electrical system or by an independent source, including a compressor with its associated pressurestat which governs it in order to maintain the air pressure required by the circuit. The compressor supplies a tank of compressed air, to which is connected at least one hydraulic cylinder whose upper and lower chambers are each connected to intermediate air and oil collecting reservoirs. The tank and reservoirs which supply the hydraulic cylinder are interconnected alternately by a two-way electrovalve in each of its two positions, while the reservoirs in turn in each position of the valve alternate their connection with the atmosphere through a filtering medium.

A tandem axle suspension in which the air pressure in an air spring (28) is controlled by a valve (40) which in turn is responsive to the load at the end of a leaf spring (12) to balance the load on a leaf spring axle (14) with the load on a tag axle (30). A crank mounting (36) connects the end of the leaf springs (12) to the valve (40). The valve (40) has a fixed valve seat (132) and a movable valve seat (116) both of which seat against a movable flat valve element (150). The movable valve seat (116) is biased against the movable flat valve element (150) in part by the load on the leaf spring (12) so that the valve seat (132) and the flat valve element (150) will separate when the load on the leaf spring axle (14) increases. The flat valve element (150) is biased against the fixed valve seat (132) in part by the air pressure int he air spring as the flat valve element (150) closes against the fixed valve seat (132) when the load on the tag axle (30) is at least equal to the load on the leaf spring axle (14). The movable valve seat (116) is biased away from the flat valve element (150) by the air pressure in the air spring so that the movable valve seat (116) separates from the flat valve element (150) when the tag axle load exceeds the leaf spring axle (14) load. An exhaust passageway (114,100,180) is provided to exhaust air from the air spring (28) to reduce an excess load on the tag axle.

A cutting tool is operatively connected with the piston of a tool positioning cylinder so as to move in response to axial movement of the piston. One end of the cylinder is connected with one end of a stroke limiting cylinder to form a closed fluid circuit therebetween. The piston of the stroke limiting cylinder has a predetermined adjustable stroke. A metering system is provided for injecting or extracting incremental fixed volumes of oil to and from the closed fluid circuit to increase or decrease the stroke of the piston in the tool positioning cylinder and thereby vary the depth of cut of the tool.