28
When properly purged, the hand pump will generate positive pressure quickly. The
construction of the hand pump means that the same pressure is generated for the test
item as for the reference test gauge.
The pressure is set to the necessary value using the fine adjustment valve. With the
pressure relief valve, the pressure can be relieved into the reservoir.
For the assessment of the test sample, the pressure displayed on the reference
manometer is compared with the measurement value.
3.1 Important notes on pressure fluctuations
It is completely normal that the pressure is not constant from the start. In the event
of changes to the pressure in the measurement device, it always lasts a few minutes
until the pressure stabilises.
This is influenced by a variety of factors. The most important influence factors are:
● Improper purging:
If there is still air in the measurement device, the pressure build-up lasts signi-
ficantly longer. Moreover, there is a fall-off in pressure over a limited period due to
diffusion processes.
● Mechanical characteristics of the pressure hose:
Bending or rolling up the pressure hose causes a reduction in the volume and thus
leads to an increase in pressure.
At high pressure, the pressure hose extends. Furthermore, enclosed air can be
diffused through the pressure hose. In both cases, a drop in pressure results.
● Temperature influence:
Temperature changes lead to a change in volume in the measurement device and
therefore to changes in pressure. The smaller the volume is, the greater the change
in pressure.
● Settling times of reference and test sample:
Observe the required waiting times after the reference and test sample have been
switched on. More information on this can be found in the corresponding operating
manual.
3 Construction and function
