180R9288_AQ109686503100en-001301 | 75
© Danfoss | 2023.12
Operation guide
Installation, Operation and Maintenance Manual for PAHT 20-90 pumps
4.
Noise from pump
Cause
Remedy
Comments
4.1 Air in fluid
4.1.1 Ensure that the entire inlet line is bled
before starting up the system.
4.1.2 Ensure that air cannot enter into the inlet
line.
Small air bubbles will accumulate and create
large bubbles causing internal cavitation and
thus making the pump very noisy.
WARNING:
The pump can only run few minutes with air in
the fluid without being damaged.
4.2 Bleeding conditions of pump
4.2.1 Follow the instructions “Initial start-up”
supplied with the new pump.
4.2.2 Ensure that the pump is completely bled
before start-up.
The pump and the inlet line must be completely
bled before start-up, otherwise the pump will
cavitate and make high noise.
WARNING:
The pump can only run few minutes with air in
the fluid without being damaged.
4.3 Min/max nominal inlet pressure
4.3.1 Ensure that inlet pressure is within
the limits specified in the Data sheet.
4.3.2 Check the pump for internal damage.
Too high inlet pressure causes too high pressure
inside the pump damaging the pistons and
eventually the pump.
Inlet pressure below min. limit causes cavitation
and insufficient internal lubrication resulting in
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 will ensure that the pump
does not start until the minimum inlet pressure
has been reached.
4.4 Pump reversing
4.4.1 Dismantle pump and check if anything is
broken or worn (See “1. No flow”, item 1.2
Pump reversing”).
WARNING:
The pump must not run without water for
more than a few seconds. If the pump
takes in water from the high-pressure
outlet line, it builds up pressure and will
eventually be damaged.
If pump rotates in wrong direction, it will take in
water from the high-pressure outlet line.
Pressure will be built up inside the pump and it
will eventually be damaged.
4.5 High rotation speed (rpm)
4.5.1 If electric motor rpm is too high, dismantle
pump and check for damage.
4.5.2 If the rpm is within the specified range of
the pump data sheet and abnormal noise
remains, dismantle pump and check for
damage.
Higher rpm than specified in the pump data
sheet results in wear of the pistons, i.e. pistons
may be damaged.
High rpm will also increase pressure pulsations
from the pump, and the noise level will increase.
If rpm is changed, noise frequency will also
change.
4.6 Outlet pressure
4.6.1 If outlet pressure is too low, check set point
of outlet pressure valve.
4.6.2 If outlet pressure is lower than mentioned
in the pump data sheet, please contact
Danfoss High Pressure Pumps technical
support.
4.6.3 If outlet pressure has exceeded its
maximum, check set point of outlet
pressure valve.
4.6.4 Check internal parts for wear/damage.
At too low outlet pressure, the pump will create
higher pressure pulsations and thus make noise.
Too low pressure also causes insufficient internal
lubrication and wear on internal parts. Pump
may eventually be damaged.
Too high outlet pressure may damage the pump.
4.7 Soft start/stop
4.7.1 Check if noise is normal when the pump is
running at operation speed.
4.7.2 If noise is abnormal at operation speed,
check internal parts (see above).
Noise frequency changes during soft start-up/
stop.
