180R9289 | AQ109686503106en-001102 | 69
© Danfoss | 2023.01
Operation guide
Installation, Operation and Maintenance Manual for PAHT 256-308 pumps
Cause
Remedy
Comments
2.1 Wear on pump
Large internal leakage due to:
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 (clear-
ance) 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 PAH/PAH F (tapwater) and PAHT/PAHT
G (ultra pure water) pumps are designed
for water 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, stop the
pump immediately.
- Check internal parts (see above).
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 wound 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 99.98%
(Beta = 5000) at 10 μm to prevent abnormal
wear of the pump.
Temperature > 50° C 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.
2.2 Low inlet pressure
2.2.1 Check that booster pump supplies the
right pressure/flow.
2.2.2 Check if filters require replacement.
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.
2.3 Rotation speed (rpm)
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.
Speeds below minimum limit (see Data sheet)
result in insufficient internal lubrication causing
wear on the internal pump parts.
2.
Reduced flow/reduced pressure
Guideline
