[138] Delockable double non-return valve (3)
The model circuit diagram
shows a delockable double non-return valve used in conjunction
with a 4/3-way valve to allow the vertical positioning of a load.
In the mid-position of the final control element shown, ports A
and B are connected to the tank. This means that the inlets A_1
and A_2 of the double non-return valve are pressure-less and both
cylinder supply lines are closed.