Reduced Flow/Reduced Pressure - Danfoss APP W HC Series Operation Manual

Service guide | Trouble shooting guide for APP, APP S and APP S 674 pumps
2.

Reduced flow/reduced pressure

Cause
2.1 Wear on pump
Large internal leakage due to:
-
2.2 Low inlet pressure
2.3 Rotation speed (rpm)
© Danfoss | DCS (im) | 2022.01
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 fit . If there is any space
(clearance) between liner and piston, liner
or piston is worn .
2 . 1 .5 Pre-treatment
Analyse fluid for content of particles .
- Check that filters are OK and working
correctly .
2 . 1 .6 Main filtration
Check that the correct filter type is used
(particles in fluid must not exceed 10 μm) .
Danfoss High Pressure Pumps supplies
filters, please contact the sales office .
2 . 1 .7 Fluid type
The APP, APP S and APP S 674 pumps are
designed for seawater operation; for any
other fluid, please contact Danfoss High
Pressure Pumps sales office for further help .
2 . 1 .8 High fluid temperature
If fluid 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/flow .
2 .2 .2 Check if filters 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 .
180R9410 | AQ282628894589en-000801 | IOM APP W HC 15-30 Pumps | 65
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 filters can be bypassed, even if they are
correctly mounted . Some filters can create
channelling where particles can pass through
the filter in tunnels . String wounded filters are
typically channelling filters . A string wounded
filter may have a filtration efficiency of only
50%, which will cause internal wear and must
always be followed by a main filter .
Insufficient filtration means that too many or
too large hard particles can pass the main filter
because it is damaged, bypassed or simply too
poor . Filtration efficiency must be 99 . 9 8%
(Beta = 5000) at 10 μm 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 fluid temperatures > 50 °C (122 ° F) .
If the pressure drop across the filters is too high,
the booster pump does not deliver sufficient
flow/pressure . No pressure or low pressure
results in cavitation and insufficient 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 insufficient internal lubrication causing
wear on the internal pump parts .