HyQuest Solutions HS40C, User Manual, Page: 26 / 37

© 2022 HyQuest Solutions 26
Appendices
Figure 1 – Depicts first stage in application of gas purge principle
Fig. Depicts first stage in application of gas purge principle - Depicts first stage in application of gas purge principle
Fig. Depicts first stage in application of gas purge principle also illustrate another feature of all pressure systems,
namely the gas endeavours to escape through any material that it is in contact with to find a lower pressure, but for
practical purposes, the system pressure reflects the lowest of the outlet pressures. In this case, gas endeavours to pass
through the walls of the tubing and fittings, through the water, but elects to take the easier path to atmosphere, which
is in effect a “massive leak”.
Therefore, it follows that in any pressure system that can exhaust to atmosphere, either through a valve or by a large
leak, the system pressure is atmospheric and will not reflect any other pressure.
Provided air or a gas that has a very similar density to air is used, then the errors from this source can be neglected.
Nitrogen is preferred as it does not promote the formation of aquatic growth.
The effect of the velocity of the gas can be observed by opening valve A, a higher pressure will be needed to force a
high volume of gas through the line, resulting in a pressure drop between valve A and the outlet. Depending on the
location of the manometer connection, the manometer will reflect a proportion of this increase in pressure.
Figure 2 – High gas flow
* Refer “Bubbler System Instrumentation for Water Level Measurement” – Report of Investigation No. 23 state of
Illinois, U.S.A
Head To Pressure Conversion
As we are not seeking to measure atmospheric pressure, but liquid head, how is the principle applied?
Simply by using two physical characteristics.
1. The tendency of the gas under pressure to “seek” a lower pressure.
26
26