6 CARE, MAINTENANCE, and TROUBLESHOOTING
6.1 Warning on Pump Direction
Th
e RAD H
2
O system cannot tolerate the reversal of
the air connections at the aerator head or the RAD7.
A check valve should be used at all times to prevent
the disastrous possibility of sucking water into the
RAD7, should a connector be accidentally reversed. If
a reversed connection occurs, the check valve
prevents the water from rising past the aerator head
by blocking its path. Do not allow the RAD7 to
continue pumping against a blocked check valve, as
this may cause damage to the pump or to the RAD7's
internal seals.
6.2 Warning on Tipping the Aeration Unit
Use a solid, stable base to hold the aerator unit when
you operate the system.
Th
e RAD H
2
O case makes a
good base when placed on a level surface.
Never operate the RAD H
2
O aeration unit in any
position other than upright! If the aeration unit tips
to any direction it may allow water to pass through
the outlet tube toward the RAD7 unit. If liquid water
reaches the RAD7, it could permanently damage
critical internal parts, resulting in an expensive repair
bill.
If water ever enters the RAD7, or if the RAD7 ever
goes swimming in the water, it will probably cease to
operate and immediate steps should be taken to
minimize the impact on the instrument.
Keep the RAD7 upright.
Th
is will prevent water from
touching the detector, which is close to the face plate
at the top of the dome. Put a piece of tubing on the
RAD7 outlet with the other end in a sink. Use the
RAD7 pump if it still works or, otherwise, an external
pump into the inlet, to blow air through the
instrument. When water ceases to be blown out of
the outlet, put desiccant upstream of the RAD7 to dry
out the air path. When the air path is fully dry (a
ft
er
dry air has been blown through it for approximately
one hour), remove the face plate from the case, empty
the water out of the case and blow dry the case and
the RAD7 electronics.
Once there is no visible water in or on the
instrument, it can be put in an oven at 50°C for a few
hours to dry out completely. Additionally, desiccated
air can be passed through the air path until the air
leaving the RAD7 drops below 10% RH. A
ft
er this
treatment further corrosion will be prevented, and
the RAD7 will boot once more and you can use the
internal RH sensor to measure how dry the air path
is. At this point the instrument should be returned to
DURRIDGE for service.
6.3 Frit Maintenance
A
ft
er performing many radon in water
measurements, the glass frit may begin to show stains
or even begin clogging due to the buildup of mineral
deposits. If the mineral buildup is light and low in
radium content, we see no reason for concern. Heavy
deposits may be removed from the frit by soaking it
in a strong acid solution, followed by a thorough
rinse with clean water.
6.4 High Humidity
While the pump is stopped, during the 25 minutes
a
ft
er aerating the sample, water molecules will
continue to desorb from internal surfaces. If the
relative humidity rises beyond 20% by the last
counting cycle, the result of the measurement will be
low by more than 5%. To prevent this from
happening, more time may need to be spent drying
out the system, with the laboratory drying unit in the
sample path, before the measurement.
A
ft
er the initial purging of
fi
ve minutes or more, the
humidity can be monitored by starting a SNIFF test
(
[Setup]
→
[Protocol]
→
[Sniff]
[Enter]
) and
going to the status window (
[Test]
→
[Status]
[Enter]
and pressing the right arrow twice).
Th
e
relative humidity is displayed in the upper right hand
corner.
Watch the humidity as it comes down below 10% RH.
With experience you will learn just how long to keep
the run going. In any case, the humidity must come
down to 6% and you may
fi
nd that 5% or lower is
necessary.
At the same time as the humidity is coming down,
you can go to the
fift
h status window to observe the
count rate in Window A. Provided that you have
purged all the radon out of the system, the window A
count rate will be due to residual 218-Po on the alpha
detector surface.
Th
is will halve every 3 minutes until
Section 6
Care, Maintenance, and Troubleshooting
25
