Grundfos DMH 251 Installation And Operating Instructions Manual page 34

14. 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 Alldos!
Fault Diagnosis
No motor sound or vibrations.
Fan is not rotating.
When the oil-filling screw (F) is
removed, use the dipstick to observe
No dosing flow
a calm oil surface. There is no
even at a low
"sloshing".
counter-pressure.
Oil level too low. See oil dipstick (F).
(Pump is running
No reaction of the overpressure
without any noise).
valve if the suction line is closed.
No dosing flow on the discharge
side.
The overpressure valve reacts
independently of the dosing flow
adjustment (10 % to 100 %).
The diaphragm protection system
No dosing flow
(AMS) responds.
even at a low
The overpressure valve reacts
counter-pressure.
independently of the dosing flow
(Pump is running
adjustment (10 % to 100 %).
noisily although the
overpressure 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.
34
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
adjusted pressure at the overpressure
valve.
Discharge valve is installed in the
opposite direction of the flow. Observe
the arrow 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
deaerated.
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
corrosive 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
11. Start-up / shutdown
Deaerate the dosing head.
Fill/exchange the tank on the
suction side.
Open the valve.
Adjust the overpressure valve
higher, but only if the pump is
designed for this. Never block the
overpressure 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
number; use valves with bigger
nominal width; realise positive inlet
pressure.
Clean and grease well all parts
using oil according to regulations.
Then install a new diaphragm.
Uninstall the discharge valve.
Dismantle and clean, or if the bars
of the ball guide are worn, replace
the valve.
.