3B SCIENTIFIC PHYSICS U104001 Instructions D'utilisation page 26

11.2 Examine threaded bush.
The threaded bush in the frame is subject to slow but
constant wear, and therefore the axial play must be
checked once a year:
•
Release the pressure from the measuring cell and
adjust the piston to the 10 mm position.
•
Using a vernier caliper, determine the minimum
and maximum distance between the handwheel
flange and frame; to do so, first wind in the
handwheel and then wind it out.
If the two distances differ by more than 0.3 mm, then
the bush needs to be replaced.
11.3 Replacing the threaded bush
Additionally required:
1 Threaded bush from set of seals (U10402)
The threaded bush is to be replaced no later than
every ten years even if the limit of wear has not been
reached (tests on a rig failed to produce any measur-
able wear [<0.05 mm] after 1000 cycles), because
reliable data on the long-term stability of the plastic
used (POM-C) are not yet available.
•
Depressurise the measuring cell.
•
Unscrew the fixed scale.
•
Undo the grub screw of the handwheel flange and
remove handwheel.
•
Loosen the four screws in the cross piece of the
frame and remove it along with the threaded
bush by winding it down the axle.
•
Unscrew the lubricating nipple (size SW 7) and use
a 3-mm Allen key to loosen the threaded pin
screwed in across the threaded bush by 4 turns.
•
Knock the threaded bush out from the side of the
handwheel using a suitable mandrel. Alterna-
tively insert an M14 screw loosely into the bush
and force the bush by hitting the head of the
screw.
•
Fit the new bush such that the cross piece is
aligned with the lubrication nipple.
•
Clamp the bush in a vice (with flat jaws or suit-
able insert).
•
Screw back in the threaded pin (min. 6.0 mm
countersunk) and the lubricating nipple.
Bush material: POM-C = Polyoxymethylene copolymer
Oversize (press fit): 0.05 – 0.1 mm.
12. Changing the seals
Additionally required:
1 Allen key (6 mm)
1 Set of seals for critical point apparatus U10402
consisting of
1 Conical seal,
1 Circular grommet,
1 Grommet 78x78 mm
4 Copper gasket washers
1 Threaded bush
After a certain period of time, it may be necessary to
replace the conical seal or other seals, especially if the
equipment has been exposed to direct sunlight.
12.1 Dismantling the equipment:
•
If necessary, allow the equipment to cool and
wind the handwheel back till the lowest possible
is present.
•
Release the test gas through the flush valve and
shut the flush valve.
•
If necessary, dismantle the tubing.
•
Open the regulating valve.
•
Wind the handwheel back till it has come to a
position of 25 mm.
•
Tilt the equipment to the right and place it in an
upright position on a suitable surface resting on
the handwheel and the edge of the equipment
base.
•
Use the Allen key (6 mm) to uniformly loosen
each of the four screws in the valve plate by 1/8
of a turn till the tension has been reduced.
•
Unscrew and remove the screws.
•
Also remove the copper gasket washers.
•
With increasing force, twist the valve plate to the
left and right till the seals have been loosened.
Do not twist the regulating valve.
•
Remove the valve plate (the measuring cell might
still be sticking to the plate).
•
Twisting the equipment some more to loosen the
remaining seals between the measuring cell and
the cylinder and between the measuring cell and
the valve plate.
•
Twist the guide tube to remove it from the coni-
cal seal.
12.2 Cleaning the dismantled equipment:
Castor oil can be removed quite easily by using white
spirit. However, white spirit attacks the acrylic of the
casing and measuring cell. Use a (mild) washing-up
liquid solution to remove greasy finger marks and
other impurities. New seals too should be cleaned
with white spirit and a washing-up liquid.
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