HAWE Hydraulik SE, Munich, has developed a new connection block for the PSL proportional directional spool valve that allows farmers to connect different trailer configurations to their tractors. The hydraulic system of loaders, mowers, potato harvesters etc. stays independent of the tractor's hydraulics, no matter whether the tractor's system uses a variable or fixed displacement pump because the connection block can supply the trailer unit through both pump types. The 3/2 seated valve that is fitted to the connection block allows the operator to switch manually and easily between the two. The option for an electrical switch is also available.

The connection block furthermore allows adjusting between two pressure levels without the need to add another component for the second pressure level. This keeps the connection block's space requirements very low. While the first pressure stage for the input pressure remains constant, the second stage's pressure level can be lowered to that of the hydraulic consumer.

The connection block is a variant of the proportional directional seated valve, type PSL. These valves are suited for such hydraulic proportional functions as hoisting, lowering, and tilting cutters or opening and closing the loader's tailgate. Seated valves, on the other hand, offer more advantages for individual functions as they provide not only a more cost-effective solution, but are also safer and less demanding in their power uptake. Because they do not leak when closed, pressure remains constant and the positioning cylinders, of the tailgate for example, remain in the position they are intended to stay. As the pressure is maintained at a constant there is no need for the pump to refeed and thus it takes up less fuel. The seated valves are simply flanged-on to the connection block without the need for feed and discharge lines.

The connection block is designed for operating pressures of up to 420 bar at a maximum volume flow of 80 liters/minute. The auxiliary functions provided by the seated valves can be operated up to 315 bar and a volume flow of 20 liters/minute. As operating pressures of agricultural machines are around 250 bar, the components' longevity can be safely assumed.

HAWE Hydraulik at the Agritechnica 2011
November 13-19, 2011
Hall 25, Stall L04
Trade Fair Hanover