Dometic RO400 Service Manual page 25

symptom
c) Alarm, too low pres-
sure due to a high
pressure drop in the
filters.
d)
Alarm, too low
pressure due to
too low feed pres-
sure.
12
tROuBlesHOOting
possible error
Check/action
codes
• Has filter I been replaced?
• can a high particle load be
expected?
• Is the coarse filter clogged?
• check valves for inlet water
before the water purifier is
opened.
• Measure the dynamic feed
pressure using the special
service tool.
• Is the water temperature
high, thus resulting in a very
high capacity of pure water
production?
• Is there reason to believe
that the feed pressure varies
a lot?
• Are there other users at the
net that occasionally might
draw large amounts of
water?
• Are there other filters,
valves etc. installed prior to
the water purifier that can
reduce pressure?
Remedy
If filter I has not been changed or if the parti-
cle load is high, change filter I and try again.
If filter I has been replaced but the problem re-
mains, remove filter II. If this solves the issue,
install a new filter II. (It can also be concluded
that the inlet pressure sensor is OK).
Clean the coarse filter.
Booster pump
If the water pressure is frequently low, a
booster pump is a solution. Make sure that
filters, installed prior to the water purifier, do
not add to the pressure drop.
Reduced pure water flow
A very high pure water flow will increase the
requirements of high enough feed pressure.
Therefore, it is possible to reduce the pure
water flow by an external valve. (It should not
be restricted too much if a accumulator tank is
used since this will result in on/off operation.)
Reduced working pressure
Reduce the working pressure by manipulat-
ing the pressure regulating valve. A decreased
working pressure will reduce the water flow.
The drawback is that there is no "pressure"
buffer. If, for example, feed water temperature
is reduced or if the membrane is scaled, the
flow will immediately go down. Normally, this
would result in an increased working pressure
and maintained capacity.
Accumulation of water
If the problem is due to an almost complete
absence of water, consider (for a short period
of time) using an accumulator tank - pres-
surised with a check valve or open tank
combined with a pump - that can provide the
product with water.
External low pressure shut-down
Use an external inlet pressure sensor at the
inlet side combined with a valve on the pure
water side that cuts the pure water flow when
the feed pressure is too low.
Temporary disconnection
As a drastic measure consider temporarily dis-
connecting the water purifier at periods when
the water pressure is low. This will reset the
low pressure alarm. Note that if this is made to
frequently, the pump may be damaged.
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