Explanation of the three way hydraulic valve of
the VPLER and VPLEV platen presses.
These electric hydraulic presses are powered by an electric motor
that drives an "oil-pump". This oil pump activates the hydraulic
cylinder that in its turn, moves the platen up and down. The action
of this hydraulic cylinder is controlled by a manually operated three
way valve.
- When the machine is turned on, it is advisable to have the
lever of the valve in neutral position. (on the images below;
position B).
- The hydraulic pump is activated by turning the switch, that is
attached to the electric motor. If the lever of the valve is in
neutral position, nothing will happen. There will be only a
certain vibration of the hydraulic pump.
- When the lever of the valve is turned into "position C", the
platen will come down slowly. Please be careful when you do this.
Verify that there are no strange opjects between the two platens.
If there are such objects, this may lead to damage of the press
and even accidents. The platen will continue to go down until it
reaches the "printing sandwich" or the lower platen. As soon as it
hits the sandwich the oil pressure in the system will rise, as can
be read on the gauge. The pressure can go up until the maximum
allowable pressure is reached (700 bar). At this point the top
platen exercices a force of 25 tons (25.000 kgs) The pressure will
never exceed this point because an "overflow" valve starts to
function. (the overflow valve is indicated on the image).
This overflow valve will in this system also be used as a means to
limit the pressure, if that is necessary for a certain print. If a
print is small, only a fraction of the 25 tons is needed. Also the
proportion of the surface that is actually in contact with the
paper is important. A print with only lead type needs far less
pressure than a general woodcut of the same size.
In a try out session the correct pressure should be determined.
The overflow valve needs to be adjusted then in such a manner that
it starts overflowing when the desired pressure is reached.
If this is accomplished the whole series of that same print can be
done without re-adjusting the pressure between the printing
cycles.
- When the top platen reached the printing sandwich, and the
desired pressure is reached, the overflow valve will start its
function. At this point it is wise to switch the valve back into
neutral position. In this neutral position the system keeps its
pressure. If the pump remains too long in the "overflow mode" it
may lead to overheating of the oil. In the neutral position the
oil will not heat up! Sometimes it it better for the transfer of
the ink to the paper if the pressure is maintained for a few
seconds. This system allows you to do that.
- When the platen must come up again, turn the valve
slowly into position A. This needs to be done slowly,
especially if high pressures are involved. A sudden release of the
pressure produces a "shock" in the system. This is not dangerous
in any way, it is only uncomfortable. (the gauge is filled with
oil, to neutralize the shock in its mechanism).
- The platen will go up until it reaches the long screws (metric
16mm). This screws can be turned up and down. (you will have to
climb on the machine to do it however.) These two screws have to
be always on equal hights.
If your printing sandwich is normally only 3 cm thick, you do not
need the maximum space of 14 cm between the platens. This will
only be inefficient. With the two screws at the right position you
can limit the upwards movement of the top platen.
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