Danfoss APP 46 Installation, Operation And Maintenance Manual page 73

Operating guide
2. Reduced ow/reduced pressure
Cause
2.1 Wear on pump
Large internal leakage due to:
-
2.2 Low inlet pressure
2.3 Rotation speed (rpm)
© Danfoss | 2023.03
Installation, Operation and Maintenance APP 21-46 pumps
Remedy
2.1.1 Dismantle the pump.
2.1.2 Check valve plate.
Valve plate has marks/scratches on the
surface facing the port plate. Minor wear
on valve plate can cause large internal
leakage. See Index 6.1.
2.1.3 Check port plate.
Port plate has marks/scratches on the
surface facing the valve plate. Minor wear
on port plate can cause large internal
leakage. See Index 6.2.
2.1.4 Check cylinder barrel.
Liners in cylinder barrel may be scratched
or worn. Insert a piston in the liner and
check the t. If there is any space
(clearance) between liner and piston, liner
or piston is worn.
2.1.5 Pre-treatment
Analyse uid for content of particles.
- Check that lters are OK and working
correctly.
2.1.6 Main ltration
Check that the correct lter type is used
(particles in uid must not exceed 10 m).
Danfoss High Pressure Pumps supplies
lters, please contact the sales o ce.
2.1.7 Fluid type
The APP, APP S and APP S 674 pumps are
designed for seawater operation; for any
other uid, please contact Danfoss High
Pressure Pumps sales o ce for further help.
2.1.8 High uid temperature
If uid temperature is above 50 °C (122 ° F),
stop the pump immediately.
- Check internal parts (see above).
2.2.1 Check that booster pump supplies the
right pressure/ ow.
2.2.2 Check if lters require replacement.
2.3.1 If VFD-operated, check frequency.
2.3.2 Check that rotation speed of the electric
motor is as stated on name plate on
electric motor. Check that the motor rotor
winding is not damaged.
Comments
Typical signs of wear:
Polished surface all over the swash plate.
Normally, only half of the swash plate = the
pressure side is polished. See index 6.3.
If the ring is missing, the piston is very worn.
The lters can be bypassed, even if they are
correctly mounted. Some lters can create
channelling where particles can pass through
the lter in tunnels. String wounded lters are
typically channelling lters. A string wounded
lter may have a ltration e ciency of only
50%, which will cause internal wear and must
always be followed by a main lter.
Insu cient ltration means that too many or
too large hard particles can pass the main lter
because it is damaged, bypassed or simply too
poor. Filtration e ciency must be 99.98%
(Beta = 5000) at 10 m to prevent abnormal
wear of the pump.
Temperature > 50 °C (122 ° F) will cause wear on
internal pump parts. Mount a temperature
switch and check its set point / function. The
temperature switch will ensure that the pump
stops at uid temperatures > 50 °C (122 ° F).
If the pressure drop across the lters is too high,
the booster pump does not deliver su cient
ow/pressure. No pressure or low pressure
results in cavitation and insu cient internal
lubrication causing wear on internal pump
parts.
Mount a low-pressure switch in front of the
pump and check its set point/ function. The
low- pressure switch ensures that the pump
does not start until the inlet pressure has
reached 1 bar.
Speeds below min. limit (see User manual)
result in insu cient internal lubrication causing
wear on the internal pump parts.
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