Fault Finding Chart - Grundfos DMH 25X Installation And Operating Instructions Manual

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