3B SCIENTIFIC PHYSICS U104001 Instructions D'utilisation page 24

10. Degassing the hydraulic fluid
Owing to the inevitable diffusion of the test gas
through the protection valve, the pressure in the
measuring cell slowly decreases over a long period.
The gas diffusing through the protection valve first
dissolves in the hydraulic fluid but does not have any
significant influence on the measurements.
However, if the test gas is removed from the equip-
ment (for storage of the equipment) and the pressure
of the hydraulic fluid consequently falls to the ambi-
ent pressure, then the test gas will escape from the
hydraulic fluid due to Henry's law. This leads to a
gradual increase in pressure in the oil chamber which
must be avoided at all costs as there is no back pres-
sure in the measuring cell. On account of this, it is
necessary to cleanse the hydraulic fluid of all gas
before storing the equipment.
To degas the hydraulic fluid, the oil is made to boil in
a vacuum. Since the pressure difference on both sides
of the protection valve should not exceed a particular
limit, it is necessary to maintain, as best as possible,
the existing underpressure constant on the gas side.
Additionally required:
1 Castor oil approved for medicinal use
1 Vacuum tube, 6 mm internal diameter
1 Stopcock (or variable-leak valve)
1 Vane-type rotary pump
1 Open-end spanner (14 mm), 1 pair of tweezers
Absorbent paper, cardboard box
Storage of the equipment:
•
If necessary, allow the equipment to cool. Wind
the handwheel back till the lowest possible is pre-
sent.
•
Release the test gas through the flush valve and
shut the flush valve thereafter.
•
If necessary, remove the gas supply pipe and
attach the gas connection fittings.
•
Unscrew the vernier scale.
•
Open the regulating valve.
•
Wind the handwheel so that piston moves in till
an excess pressure of 1 bar has been attained.
•
Shut the regulating valve.
•
Wind the handwheel back by two turns.
•
Place the equipment with the manometer facing
downwards towards the ground). The manometer
should rest on a support approx. 6-cm-thick (see
Fig. 6).
Caution: the piston should never be wound out to
more than 25 mm, since the guide tube may slip out
during subsequent operations.
Fig. 6: Storage of the equipment for oil filling
d
Fig. 7: Dismantling the safety valve
(c) counter nut, (d) valve cap, (e) compression spring,
e.g. U10401
(f) hexagonal piston, (g) steel ball bearing
Dismantling the safety valve:
•
Loosen the counter nut (14 mm) and use a screw-
driver to remove the valve cap (see Fig. 7).
•
Remove the compression spring, the hexagonal
piston and the steel ball bearing in succession
with a pair of tweezers and store them in a safe
place, for instance in a cardboard box.
Assembly of the oil filling device:
•
Loosen the valve nut of the oil filling device, re-
move the cover and place the valve nut above the
safety valve (see Fig. 8).
•
Do not screw the oil filling device on too tight (the
gasket ring should not be squeezed out).
•
Open the regulating valve.
•
Wind the handwheel inwards to its end position
up to the frame (if necessary, loosen the vernier
scale). Subsequently wind the handwheel out by 3
turns.
•
Place absorbent paper underneath and fill the oil
container with castor oil to no more than half
way.
•
Screw on the cover of the oil filling device with
the valve nut.
Connection of vacuum pump:
•
Connect a plastic hose with 3 mm internal diame-
ter to the gas connection fittings of the equip-
ment and the smaller connector of the oil filling
device.
10
c
c, d
e
f
g