Assembly and installation
21
HYDROKRAFT OPERATION MANUAL PVW 250+360
E-PUIO_II001-E April 2021 www.eaton.com
5.9 Case drain and Case pressure
5.9.1 Drain line requirements
Looping the drain from the highest point will ensure that
air is purged, and all parts are bathed with oil.
The case drain must be taken from the highest drain
port on the unit and looped above the reservoir oil level.
Momentary high drain flows however may cause foaming
of the reservoir fluid so drain lines should terminate
below oil level. If necessary, a small anti-siphon hole can
be drilled into the drain line to prevent fluid loss when the
pump is removed.
Standard check valves should not be fitted into the drain
line, especially at larger pumps, due to the increased back
pressure created and the fact that in certain instances, a
reverse fluid flow in the drain line is necessary.
Individual connection of drain line of each single pump
is the preferred option, to avoid pressure peaks by
backpressure or dynamic flow impacts.
If a collecting line is used, a suitable diameter must be
chosen. Depending on length of drain line, flow velocity
should not exceed 1 m/s at max. drain flow.
Recommeded drain line sizes
Drain line sizes
drain
port size
L1
drain
port
size L2
max drain flow
[l/min] at 300 bar
min. internal pipe
diameter in mm for
v max=1,0 m/sec
piping short distance -
length < 2 m + max.
2x 90
o
pipe elbows
piping long distance length
> 2 m or s > 2 pcs
90
o
pipe elbows
PVWS-250
15/8"-12
G1 1/4"
16-20
20,6
28x2
35x2
PVWS-360
15/8"-12
G1 1/4"
20-25
23,0
28x2
35x2
5.9.2 Case pressure specification
Max. case pressure is mainly defined by pressure
capability of shaft seal.
Lifetime of shaft seal is depending on shaft speed of the
pump, fluid, case drain pressure and others. For max.
allowable values please refer to Ch 3.4 “Technical data”.
In addition to the overall case pressure limit, defined
by shaft seal limit, for open circuit pumps there is an
additional limit related to the differential between case
pressure and inlet pressure. This should not exceed 0.5
bar. Excessive case pressure over inlet increases forces
between shoe and piston and might affect/decrease
lifetime of this combination
