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It is above all worth
recalling that the sealing lip must always
be turned toward the fluid to be retained, or to the side
exerting a pressure. A single gasket is generally sufficient to
guarantee the seal; however, for vertical or inclined shafts
(with a seal above the fluid level) the installation of two
opposing gaskets is recommended: the chamber created by the space
between the two gaskets must periodically be filled with grease. The
shaft seal must only serve as a seal, without any supporting function
for the mechanical parts; the latter must be
prevented from coming into contact with the sealing lip, because
this may considerably shorten the lifetime of the gasket,
as well as compromise its sealing action. You are reminded
that it is always necessary to carefully lubricate the
shaft seal with grease before installing it, to prevent it from
running dry during the initial revolutions of the shaft. The
grooved shaft seals are on the other hand not to be lubricated
with grease but with oil, as the grease would tend
to fill out the grooves and thus nullify their effectiveness.
9.1 Instructions for installation
To ensure an optimum performance of the shaft seals, the following
instructions for assembly must be adhered to:
1) Check the seat to verify
the absence of burrs or grooves, especially
longitudinal grooves.
2) Check the shaft to verify the absence of any burrs, which may
affect the sealing lip. If the sealing lip must pass over key
slots, sharp edges or threads, a special mounting expander
must be provided.
The expander diameter
must exceed the shaft diameter by 0.4 - 0.8 mm and
have a finely ground surface.
3) Grease the sealing
lip and the outer surface of the shaft
seal
with clean grease. As already seen, if RP and RD type shaft
seals are used, 70%
of the space between the two shaft
seals must be filled with grease.
4) Mount the shaft seal on the seat by pushing it under uniform
pressure up to the stop, while using the special expander. It is good practice, wherever
possible,
to use pushers equipped with a mechanical support on the outer seat. This prevents directing the fitting thrust of the press on the
gaskets after setting
them in place against the stop. This thrust may deform
the gaskets, thus compromising their sealing action.
It is also advisable to position the gaskets directly on
the pushers, using the friction between the sealing lip and
the central spine, so as to later
perform the fitting by
ensuring a proper alignment between
the pusher and the housing.It should be noted that during the fitting
the effort must be exerted
as closely as possible to the outer diameter of the shaft
seal, giving particular attention to its perpendicular position
with respect to the axis of the bore. The use of sealants materials
between the gaskets and housings, while practiced,
is not recommended. No matter how accurate the
sealing operation, some residues of adhesive may reach
the sealing area, thus causing damage and immediate fluid leakage.
5) In cases where the shaft
seal must first be inserted over the
shaft and then into the seat, take care that during the time
between the two operations the shaft seal is not loaded by the weight of
the shaft.
6) Take care to mount the shaft seal on the shaft in a concentric and
perpendicular fashion.
Fitting errors may
lead to instant fluid losses or non-uniform wear of the shaft
seals, with a resulting reduction of seal life.
7) After the installation is completed, ensure that the sealing lip is
fitted in its natural position and above all that the Garter spring is
properly positioned in its seat; the loss of the spring may cause
damages.
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