Page 262 - The Tribology Handbook

Sealing against dirt and dust B20

Table 20.3 Sealing of reciprocating parts
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Method Description Comments
A relay system as in Figure 20.1 The hydraulic device is built into a High level of protection. The primary
housing and a relay system converts the hydraulic seal functions in clean
reciprocating into rotary motion. The conditions
rotating parts are sealed as shown in
Table 20.2
A flexible covcr system as in Figure 20.2 A flexible cover is mounted over the main At maximum speed of operation provide
hydraulic seals and means provided for piping to limit pressure difference to
breathing clean air through piping from 35 kN/m2 (5 Ibf/in2) between inside and
the inside of the cover to a clean zone or outside of cover. The hydraulic system is
through an air cleaner. The cover dependent on the cover and although
material is highly oil resistant and small pin-holes will not seriously reduce
preferably reinforced with fabric protection in dry conditions they will
cause early failure if present when
operating under water or in wet soil
conditions
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Standard chevron seals, '0' ring.s etc. Non metallic reciprocating seals used Suitable where some loss of hydraulic fluid
singly or in groups. All sliding parts is not critical. An adequate reserve of
through and adjacent to the seals highly hydraulic fluid must be provided to keep
corrosion resistant system full
Flexible metallic or non-metallic Hydraulic system sealed off completely Very high level of reliability but restricted
diaphragm to small usable movements depending
on diameter of diaphragm

FLEXIBLE COVER
OIL RESISTANT
REINFORCED WITH FABRIC

RECIPROCATING
SEALED
HOUSING
1 SYSTEM 1
RECIPROCATING
HYDRAULIC

PRIMARY HYDRAULIC SEALS
BREATHER PIPE TO CLEAN
Y\ ZONE OR AIR CLEANER

RELAY SHAFT Figure 20.2 A vented flexible cover system
ROTARY MOTtOlU
SHAFT SEALS AS IN TABLE 20.2
Figure 20. I A relay system for reciprocating motion
B20.3