The Hand Valve; The Compressor - fischertechnik Profi Pneumatic II Manual De Instrucciones

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Lifting Platform Experiment 3 (see Construction Manual p. 7):
Now connect the hand pump to the tube which leads to the lifting
platform. As a result, now you can pump so much air into the lifting
platform's cylinder that this (cylinder) is completely extended.
Now we have only one problem. If we want to lift the lifting platform
upward, the air has to be pumped into the cylinder through the lower
connection. If the lifting platform is to be lowered again, the air has to
be directed through the upper connection. Of course, it is much too
troublesome to constantly change and reconnect the tube. There is a much
better solution.

2.5 The hand valve

This valve has 4 connections:
A P
The middle connection (called Connection "P") is the supply for the com-
pressed air. The left and right connection pieces (A and B) are for the tubes
to the cylinder. The short connection on the lower side is the deaeration
("R"). This enables the air to escape, which comes back from the cylinder
(the so-called "exhaust" or "outgoing" air). The valve has three switch
positions (middle – left – right). In the science of pneumatics, a valve with
4 connections and three switch positions is called a 4/3-way valve.
Lifting Platform Experiment 4 (see Construction Manual p. 8):
Close the valve as described in the Construction Manual.
If the switch is in the middle position, all connections are closed, and
the lifting platform does not move. If you turn the valve switch to
the left, and then pump with the air pump, the lifting platform
lifts upward. If you turn the switch to the right, you can move the
platform downward again.
The following figures explain how the air flows into the different switch
positions through the valve:
Left
P
R
12
B
R
Middle Right
P
R

2.6 The compressor

Of course, pumping by hand
is tiring after a while.
There is a much more
elegant solution for this.
Build the compressor
as described in the
Construction Manual
on page 11.
Lifting Platform Experiment 5 (see Construction Manual p. 9):
Now attach the compressor on the base plate of the lifting platform
model to the two specially provided red modules. After that, connect
the compressor to the lifting platform instead of the hand pump.
It is important that you utilize a 9V alkaline battery as power supply.
A "normal" 9V block conks out after only a few minutes. Of course,
the "fischertechnik Accu Set" (Art. No. 34969) — which has consider-
ably more power than the 9V block, holds much longer and is able to
be charged over and over again — is much more suitable.
After turning on the compressor, you have to wait ca. 15 seconds
until the air chamber is filled. Then you can move the lifting platform
up and down without having to constantly pump by hand at the
same time.
We utilize the small pneumatic cylinder with the black piston rod as a pump
for the compressor. The piston rod of this unidirectional cylinder is able to
be moved easier than the piston rod of the large cylinder, and is thus able
to be propelled by means of the fischertechnik motor. The air chamber
ensures that there is always enough compressed air available for operating
the pneumatic cylinder. The pressure generated by the compressor amounts
to ca. 0.5 bar. The compressor cylinder piston always has to be able to
move smoothly. If necessary, it can be sparingly lubricated with a small
drop of acid-free oil (e.g. silicone oil). If the compressor will not be used
for a lengthier time span, it is recommended to remove the drive belt,
because this wears out over time and can thus slip through.
Lifting Platform Experiment 6 (see Construction Manual p. 9):
Utilize the compressor without air chamber. In addition, lay out a
20 cm-long tube, which extends from the check valve directly to
Connection P of the hand valve.
What changes during operation of the lifting platform?
Observation:
The lifting platform "bucks" during extension as well as during
retraction, because the pump intermittently pumps air into the
P
system. The air chamber equalizes this pressure surge. That's
why the motion with the air chamber is much more uniform.
R