DIGITEL High Volume Sampler Maintenance

Maintenance of the High Volume Samplers:

Digitel HVS DHA-80 requires minimum maintenance. However, depending on the air pollution degree and climatic load upon installation site, inspection of the sampler associated with cleaning is necessary.
In particular, the following activities shall be performed:

Cleaning:
High-volume samplers must be cleaned on regular basis. Cleaning intervals strongly depend on the installation site characteristics and they have to be determined by the operator. They may range from one month up to one year.
During cleaning, the instrument should be off power.
To clean the instrument, a dry cloth should be used. At heavy contamination, the cloth should be wetted with a commercial window cleaning product. Make sure that the instrument is dried up before starting up again.
Avoid using solving and scrubbing cleaning products!
The flow meter glass tube has to be visually inspected. In case of broken filter or negligent sampler operation without a filter inserted, contamination can also take place. In case of any doubt, the tube has to be removed and cleaned.
Due to its difficult accessibility, the funnel-shaped flow chamber upper part located before the filter, can only be cleaned in combination with possible changer apparatus service works. As this section of air-sample path shows a much larger inner diameter, it is less affected by deposits, as a rule.
The inlet tube interior has to be inspected for wall deposits and in case of doubt, cleaned, using a cloth. As a cleaning liquid, we recommend water and/or spirits.
TSP sampling probes („open ring-slot“ according to VDE or „EMPA/UBA“ - cylindrical probes) have to be checked for dust deposits and cleaned, if possible. Normally cleaning using a wet cloth is sufficient.

——————————————————————————————————————————————————————————————————————————————————————————————————

Exchange of sealing rings
The transition areas between the above-stated path separate section of the air probes are equipped with sealing rings (O-rings).
Special attention has to be paid to the sealing ring of 44 x 3 mm at the sampler inlet muffle, as well as to the glass measurement tube O-rings (50.4 x 3.53 mm). These O-rings have to be checked and possibly replaced after 2 to 3 years of operation.
The sealing ring of 150 x 3 mm at the bottom flange of upper part of the flowing chamber should be inspected (by a DIGITEL service engineer) and possibly replaced after 2 to 3 years of operation.
Sealing rings (150 x 3 mm) at the filter holder bottom part is coated with an anti-friction layer. They have to be regularly checked when a new filter is inserted and rubbed, using a dry cloth. When this layer is worn out or in case of increasing sticking tendency, it should be renewed. We recommend to replace these sealing rings annually.

——————————————————————————————————————————————————————————————————————————————————————————————————

Tightness test. Checking of volume-flow calibration
At start up, displayed blower load level, converter frequency, filter type and flow will be recorded. Sudden insufficient blower capacity under the same conditions, is caused by leakage in the air-sample path (after the filter).
Another very simple option for testing the sampler tightness consists in closing the sampler at the inlet muffle with the inlet tube removed or by inserting an air-impenetrable cardboard instead of the filter paper to the filter holder and switching the blower on. In both cases, the flow meter floater must not be lifted from its resting position at the bottom of the measurement tube. Hereby the blower must be run up to its maximum capacity in order to reach the overload condition.
The checking of the volume flow simultaneously represents a check of tightness. These procedures have to be taken approximately every two months.
The second flow meter of the same construction as used in the sampler itself, controls the volume flow and is installed onto the sampler as „transfer standard“ instead of a pre-separator or a suction pipe. With a new round filter paper inserted, the positions of floaters are compared by switching the blower on. At variations of the set point, originally calibrated on the flow meter of the sampler, the checking of tightness should be performed.
——————————————————————————————————————————————————————————————————————————————————————————————————

Dusty round filter homogeneous deposit
Upon removing dusty filter papers or during weighing, filters have to be subject to visual inspection for homogeneous deposits. Drop-like spots in the filter centre, as a rule, indicate inoperable probe heating, or/and a defective inlet muffle O-ring. Bright spots on the filter paper rim are attributable to defective sealing of the flowing chamber upper part with the filter holder upper surface (service works are definitely required!).
——————————————————————————————————————————————————————————————————————————————————————————————————

Blower
The blower has the average MTBF (average time between failures) of 36 000 hours. It is maintenance-free. However, for instruments under operation for longer than two years, an occasional acoustic inspection of the blower by opening the blower section, is recommended to prevent a possible blower blocking.
Special attention has to be paid to excessive (unusual) noises generated by the blower (scrubbing, screeching).

——————————————————————————————————————————————————————————————————————————————————————————————————
Filter preparation
Reliable and reproducible measurement results can only be achieved by using filters that are carefully conditioned before and after sampling.
Filters are pre-weighed and provided with a date. In order to enable a checking during the operation by which a correct assignment of filters is possible, the filters are inserted into the filter holder, marked according to respective dates. The spring collar is removed from the filter holder (using pliers) while a Teflon ring is laid on a clean surface by using forceps. New filters are removed from the filter magazine by using forceps and laid into the filter holder. Then the Teflon ring should be laid again (using forceps) on the ring of the spring collar by using pliers. Now the filter holder is ready for transport to the sampler. During transporting the filter, no impurities should get onto the filter (therefore refer to standard EN 12341 Annex C).
The polluted filter is removed from the filter holder, using forceps, and inserted into a simply folded parchment envelope.
Warning!
It should be noted that a possible labelling of a filter holder is only permitted on its front, using a marker.
Any inscription on the filter holder on the upper or bottom sides, as well as sticking labels (on the filter holder entire surface) might cause problems with the filter exchange and is prohibited!
Please mind that no sealing ring (on the filter holder and in the flowing chamber) get in touch with inscriptions. The solvents, applied in various markers or pens, destroy the applied sealing rings! Moreover, paint residuals may result in bonding the sealing rings!
——————————————————————————————————————————————————————————————————————————————————————————————————

Maintenance pre-separators:
To avoid effects of released separated rough dust particles, the cannon surface of the impactor plate has to be permanently covered with a thin fat layer. It has to be periodically renewed. As a grease, you can use, for example: BAYSILON paste, high-vacuum grease, medium-viscous (35 g tube) and silicon high-vacuum grease, medium Merck 100 g, Article 7922 LAB.
Thereby the life cycle depends upon the proportion of rough dust in the sampled exterior air. It is recommended to clean the impactor plate after 14 sampling days, by the time the average total dust volume (TSP) on the installation side is approx. 70 to 80 g/m3. With lower TSP, the cleaning interval can be longer. You can extend the cleaning interval results by rotating the moveable impactor plate, resting on the heating holder, by approx. 15° (approx. 2 cm). Acceleration nozzles then point at the „clean“ areas between rough dust deposit settled in a circular form of the previous sampling operation.
The impactor plate can be removed simply after opening the probe upper part . It has to be cleaned with a clean cloth and its cannon surface has to be greased. An approx. 5 cm long band of grease should be equally spread on the area, using a spatula. To relieve this maintenance in the field, the impactor plate can be replaced by another plate prepared in the laboratory.
Acceleration nozzles, probe casing liners, as well as a liner behind the impactor plate with the above-mentioned TSP condition have to be cleaned after 30 flowing days.
In case of longer sampling in foggy environment it is recommendable to inspect the impactor plate for water condensate.