Table of Contents
Advertisement
Note. It is vital that the containers are not topped up.
f) Examine the sample input pipe for leaks and deterioration.
g) Ensure the drain is in good order and free from obstruction.
8.2.3 Four Monthly
Refurbish nitrate electrode – see Section 8.5.
8.2.4 Twelve Monthly
a) Service pump, tubing and capstans – see Section 8.2.8.
b) Replace all internal plumbing tubing – see Section 8.2.9.
c) Carry out the normal 4 weekly schedule not already covered
above.
8.2.5 Cleaning Sample Pipework
A common problem in measuring water samples from rivers,
treatment works, etc., is the presence of bacteriological growth in
the sample.
In the form of algae it creates a problem by growing inside tubing
supplying sample to analysers, as well as in the monitors and
associated ABB Instrumentation Ultrafilters, if used. If severe, this
growth may cause blockages in tubing or valves and/or fouling of
flowcells and sensors.
In addition, the algae may affect the concentration of the
measured parameter in the sample. This is particularly severe in
ammonia monitors, where algal growth in supply lines causes
'ammonia stripping' and a reduction in the measured
concentration. Other parameters, however, may also be affected.
It is therefore essential to maintain sterile conditions. This
requires periodic cleaning, at a frequency dependent on sample
conditions. It is suggested that a regular maintenance
programme is introduced, rather than wait for visible signs of the
presence of algal growth.
Note. Once growth is visible the problem is already serious.
The recommended agent for cleaning tubing and pipework is
sodium hypochlorite solution containing about 0.1% (1000 mg l
available chlorine.
Cleaning Solution
To prepare 500 ml of cleaning solution, dilute 5 ml of
concentrated sodium hypochlorite (NaOCl) solution (containing
approximately 10% available chlorine) with de-ionised water and
make up to 500 ml with more de-ionised water.
Note. The solution is unstable. Make only enough for
immediate requirements and discard any surplus after use.
Warning. Sodium hypochrorite is an irritant. Contact with
acids liberates toxic gas. Avoid contact with skin and eyes. If
contact occurs, wash with plenty of clean water.
Method
Where an Ultrafilter is used, clean according to the manual with a
–1
0.05% (500 mg l
) chlorine solution (i.e. half the concentration of
the above solution). Tubing between the Ultrafilter and the
analyser should also be flushed through, along with the constant
head tank.
a) Remove sensors for short-term storage before cleaning – see
Section 8.3.1
b) Remove the reagent and calibration solution take-up tubes
from their respective containers. Fill a calibration container
with the sodium hypochlorite cleaning solution, place it in the
calibration container recess and immerse the take-up tubes in
the solution.
c) Operate 'Cal' to initiate a calibration sequence to draw the
solution through the solenoid valves tubing and flowcell.
d) Remove any dislodged debris from the flowcell and clean the
constant-head unit with the cleaning solution using the bottle
brush provided. The tube between the constant-head unit and
SV1 can be cleaned with the cleaning solution using the
syringe.
e) Repeat the process using high purity water to flush out the
sodium hypochlorite solution.
If, after cleaning, there are still signs of discoloration or deposits in
the monitor tubing, it should be discarded and replaced with new
tubing throughout. In cases where the monitor tubing is blocked
or very heavy deposits are found, it may be necessary to simply
replace the tubing without attempting to clean it.
Cleaning Solution Containers
Great care should be taken to ensure that reagent and standard
solution containers are thoroughly cleaned whenever their
contents are changed, as algal growth can also occur in them.
Under normal circumstances thorough rinsing of the containers
with high purity water may be adequate. However, if there is any
evidence of algal growth, the containers should be rinsed with
sodium hypochlorite solution (containing about 0.1% available
chlorine) and thoroughly flushed out with water afterwards. A
bottle brush may be useful to remove stubborn deposits.
–1
)
It is advisable when changing standard or reagent solutions to
replace the container and remove the empty/used one for
thorough cleaning.
Note. It must be emphasised that containers which are to be
used for ammonia standard solutions must be very
thoroughly washed out after chlorine treatment because any
residual chlorine will react with ammonia and hence change
the standard concentration. In addition to thorough washing
with water, it is suggested that the containers are rinsed with
a portion of the ammonia standard before finally filling.
8 MAINTENANCE...
31
Advertisement
Table of Contents
