HyQuest Solutions HS40C, User Manual, Page: 25 / 37

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Appendices
Remove the protective tape from the end of river line tube.
Insert the end of the tube into the appropriate river line fitting on the HS40S2 and tighten both fittings. (Refer to
diagram for tightening procedure).
Open the valve to the orifice.
9.2 Appendix B Using Pressure to Measure Water Level
Gas Purge Principle
The behaviour of a gas flowing under a variable back pressure is utilised as an accurate means of measuring liquid
head.
Provided that:
1. The density of the gas is nearly the same as air.
2. The velocity of gas is low enough so as not to produce significant pressure drop down the line then the system
pressure will be equal to the back pressure.
This principle is illustrated in the following series of diagrams.
In the first example, the tube exhausts to atmosphere and hence the water manometer indicate zero pressure in the
system because it is acted on by two equal pressures- the system pressure and the atmospheric pressure