Using Small Tubing Fittings; Figure 2-1 Valco Fitting - Siemens Maxum II PD PA AP Service Manual

Using Small Tubing Fittings

Two main types of fittings are used in Maxum II analyzers for the small
detectors. The first, (Valco or Swagelock) use a metal-to-metal seal that results from
compressing a ferrule. The second, (Siemens) uses a PTFE seal and a compression ring to
create a seal.
Assembling Valco and Swagelock Fittings
The ports are machined for a 1/16" Valco internal nut. The Valco ferrule or the 2-piece
Swagelok ferrule can be used. It is important to follow the manufacturer's procedures when
cutting tubing and seating ferrules to ensure that the fitting does not leak.
Figure 2-1
Use a wheel-cutting tool (such as Supelco 58692-U) to score the tubing, and then with a pair
of straightening pliers (such as Supelco 58646) and a pair of needle nose pliers, snap the
tubing at the score line. Make certain that all tubing ends are cut square with the tube axis,
and that both the inside and the outside of the tube are thoroughly deburred; use a deburring
tool (such as Supelco 58804). Inspect the end of the tubing where the ferrule will seat for
scratches along its length. Visible scratches along the tubing where the ferrule will seat are
not acceptable, but those behind the front edge of the ferrule will not interfere with the integrity
of the fitting.
1. Slide the nut and ferrule onto the tubing.
2. Insert this assembly in the fitting detail (valve body), screwing the nut 2 or 3 turns by hand.
3. Push the tubing all the way forward into the fitting pilot so that it seats firmly.
4. Manually turn the nut until it is finger tight.
5. Turn the nut ¼ turn (90 degrees) past the point where the ferrule first starts to grab the
tubing.
6. Remove the fitting and inspect it. The ferrule may be free to spin axially on the tubing but
should have no lateral movement along the tubing. If it does, reinstall the fitting and tighten
it another 1/8 turn past finger tight. Remove, re-inspect and repeat if necessary.
Comparing Fitting Types
The Valco fitting seals the connection by 'biting' into the tubing to form a secure metal-to-metal
seal. As noted above, scratches on the tubing can compromise the sealing action and cause
leaks. To replace a Valco fitting, the tubing must be cut to remove the old ferrule. This creates
a problem when the tubing is part of a flameproof enclosure such as found on the Ex TCD
block. These tubes may not be shortened.
Maxum II Valves and Oven Components
Service Manual, 10/2018, A5E42019844001
Nut
Tube
Valco Fitting
Fitting Detail
Ferrule
Pilot
2
/ " tubing used for the
1
16
21