11. Fault finding chart
Warning
Actions that are taken to correct faults on the pump and that are not described in this manual, must only be carried out by personnel
authorised by Grundfos!
Fault
Diagnosis
Cause
Remedy
No dosing flow even
at a low counter-
pressure. (Pump is
running without any
noise).
No motor sound or vibrations.
Fan is not rotating.
Motor is not running.
Connect the power supply or replace
the motor, if blown.
When the oil-filling screw (F) is re-
moved, use the dipstick to observe a
calm oil surface. There is no "slosh-
ing".
Motor runs, but the eccentric shaft is not
rotating. No piston movement. Spiral pin
or motor shaft broken.
Remove the motor and eccentric
shaft. Replace damaged parts.
Oil level too low. See oil dipstick (F).
No reaction of the overpressure valve
if the suction line is closed.
Not enough oil in the pump.
Air is penetrating the piston flange
through the control holes.
Fill in oil. Deaerate the pump, see
section Start-up/shutdown.
No dosing flow on the discharge side.
Dosing head is not filled. Suction line
empty. Tank empty.
Deaerate the dosing head.
Fill/exchange the tank on the suction
side.
No dosing flow even
at a low counter-
pressure. (Pump is
running noisily al-
though the overpres-
sure valve reacted).
The overpressure valve reacts inde-
pendently of the dosing flow adjust-
ment (10 % to 100 %).
Valve on discharge side closed.
Open the valve.
Counter-pressure is higher than the ad-
justed pressure at the overpressure
valve.
Adjust the overpressure valve high-
er, but only if the pump is designed
for this. Never block the overpres-
sure valve.
Discharge valve is installed in the oppo-
site direction of the flow. Observe the ar-
row on the valve.
Install the discharge valve correctly.
The diaphragm protection system
(AMS) responds.
The overpressure valve reacts inde-
pendently of the dosing flow adjust-
ment (10 % to 100 %).
Valve on suction side closed.
Open the valve.
Suction filter obstructed.
Clean the suction filter.
Replace, if necessary.
Suction valve jammed (does not open).
Dismantle and check the suction
valve.
Suction valve has a too strong spring.
Use the fitting spring, or use double
ball valve for checking.
Suction valve is installed in the opposite
direction of the flow.
Observe the arrow on the valve.
Install the suction valve correctly.
The diaphragm protection system
(AMS) responds.
The overpressure valve reacts at 100
% dosing flow.
When reducing the flow ~10 % to 20
%, the overpressure valve does not
react any more.
Dosing head is not completely deaer-
ated.
Fill the dosing head completely.
Pump is cavitating (dosing liquid with too
high viscosity; dosing liquid with too high
steam pressure at operating temperature
= degassing of the liquid; suction lift too
high; wrong design of the system on
suction side).
Use a gear with a low stroke num-
ber; use valves with bigger nominal
width; realise positive inlet pressure.
Diaphragm broken (not enough oil in the
enclosure of the pump; piston flange).
Clean and grease well all parts using
oil according to regulations. Then in-
stall a new diaphragm.
Pump does not dose
or pressure relief
valve opens.
Discharge valve of pump is clogged or
ball guide in the valve is worn due to cor-
rosive or abrasive media.
Uninstall the discharge valve. Dis-
mantle and clean, or if the bars of
the ball guide are worn, replace the
valve.
41
English (GB)
Summary of Contents for DMH 25X
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