Grundfos DMH 25 Serie Montage- Und Betriebsanleitung Seite 37

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.
Dosing flow too
If the counter-pressure is low, the
small.
dosing flow increases considerably.
If the stroke frequency rises, the
dosing flow increases excessively.
Pressure gauge in discharge line.
Especially at stroke frequencies
below 15 strokes/min., e.g.
frequency converter operation.
Pressure gauge in discharge line.
Pump doses too
Heavy overdose.
much.
Overdosing at high dosing flow
settings and flows.
Cause
Suction/discharge valves dirty or leaky. Clean or replace valves.
Too much clearance between piston
and slide valve, or the stroke
frequency of the pump is too low (too
much slip).
Counter-pressure has seriously
increased. Overpressure valve is
adjusted too low.
Degassing valve (M) is not working
properly.
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 the piston and piston slide
valves. Use other hydraulic oil with
a higher viscosity (mainly for
frequency converter operation and
higher counter-pressures).
Readjust the zero point.
Correct the setting of the pressure
relief valve.
Replace the degassing valve (M) or,
if necessary, replace with ∅ 8 ball.
Readjust the zero point.
Install a pressure-loading valve.
Install a pulsation damper on the
suction side.
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