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5. Functional description
5.6 Lubrication systems
5.6.1 General
Gear pump units are generally used for
single-line systems with piston distributors.
Single-line systems with piston distributors
are total-loss lubrication systems.
5.6.2 Total-loss lubrication systems
Total-loss lubrication systems feed clean
lubricant (oil, fluid grease or grease) to one
or more lubrication points at specific inter-
vals (dependent on time or machine cycle)
during the lubricating cycle time (contact
time, pump cycle time). The quantity of
lubricant fed is measured so that the lubri-
cation points are supplied with adequate lu-
bricant during the total-loss lubrication sys-
tem's interval time to maintain a lubricant
film between the friction partners. The lu-
bricant fed to the lubrication point is partial-
ly consumed during operation due to aging,
evaporation, and leaks. An interval-controlled
supply of lubricant to the lubrication point is
required in order to ensure that the lubri-
cation point receives adequate lubrication.
Such systems are referred to as inter-
mittently operated centralized lubrication
systems.
Lubrication points cannot be cooled when
using a total-loss lubrication system.
5.6.3 Single-line systems with piston
distributors
See Figures 2 and 3
Single-line systems with piston distribu-
tors generally consist of a reservoir unit,
and here include a gear pump unit, piston
distributors, and lubrication lines. The pres-
sure-regulating valve and pressure relief
valve required for the centralized lubrication
system's operation are mounted in the gear
pump unit.
If pressure losses of greater than 10 bar
are expected in the centralized lubrication
system, for example due to expansion of
the system or due to the viscosity of the
lubricant (depending on the ambient tempe-
rature), a pressure switch should be positi-
oned before the last lubricant distributor to
monitor the centralized lubrication system.
The pressure switch monitors whether the
required pressure build-up occurs in the
centralized lubrication system during the
pump cycle time.
The pump delay time specified by the con-
trol unit or machine control unit (8 to 15
seconds are recommended; other delay
times are possible depending on the lay-
out of the centralized lubrication system)
ensures pressure build-up in the centralized
lubrication system. Pressure in the main
lubricant line must be relieved after the
pump is switched off in order to ensure
proper functioning of the piston distributors.
This is performed by the pressure relief
valve mounted in the gear pump unit. On
centralized lubrication systems with extended
main lubricant lines longer than 100 m, the
main lubricant line must be designed as a
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