Grundfos DMH 28 Serie Montage- Und Betriebsanleitung Seite 38

Fault Diagnosis
Suction valve: During the discharge
stroke, the dosing liquid flows back
into the suction line.
Discharge valve: During the suction
stroke, the dosing liquid flows back
into the dosing head.
The pump takes in less.
Dosing flow depends very much on
the pressure.
If the counter-pressure is low, the
dosing flow increases considerably.
If the stroke frequency rises, the
dosing flow increases excessively.
Fault detection: When the pump
stops, fit the degassing valve (E)
Dosing flow too
block, start up the pump. Check if
small.
the dosing flow increases.
Open the degassing valve (E) again
when the pump stops.
The degassing valves (M, E) no
longer operate. The degassing valve
(M) does not discharge any oil.
Briefly close the suction side until
the overpressure valve reacts.
Adjust the dosing flow to approx. 50
%. The piston flange conveys the oil
and the air into the tank via the
overpressure valve. New oil is
extracted from the tank and taken in
through the piston holes.
Pressure gauge in discharge line.
Pressure gauge in discharge line.
Pump doses too
Heavy overdose.
much.
Overdosing at high dosing flow
settings and flows.
38
Cause
Suction/discharge valves dirty or leaky. Clean or replace valves.
The piston lip seal is worn out (usually
after a long period of operation or if the
oil is dirty).
Too much clearance between piston
and slide valve, or the stroke
frequency of the pump is too low (too
much slip).
The O-rings of the degassing valve (E)
are faulty.
The degassing valve (M) discharges
too much oil.
Air has accumulated in the piston
flange. The air cannot be evacuated.
Counter-pressure has seriously
increased. Overpressure valve is
adjusted too low.
Counter-pressure has seriously
dropped.
Inlet pressure of suction line higher
than counter-pressure of discharge
line.
Too big dynamic in the suction line.
Remedy
Replace grooved ring.
Replace the piston and piston slide
valves. Use other hydraulic oil with
a higher viscosity (mainly for
frequency converter operation and
higher counter-pressures).
Replace O-rings.
Caution! If the O-rings are
incorrectly installed, or if the
degassing valve (E) is adjusted
during operation, this may damage
the O-rings.
Correct setting and replace
degassing valve (M), if necessary.
Check setting on degassing valve
(M), replace degassing valves (M,
E), if necessary.
Readjust the zero point
(DMH 281-288).
Correct the setting of the pressure
relief valve.
Readjust the zero point
(DMH 281-288).
Install a pressure-loading valve.
Install a pulsation damper on the
suction side.