HYDROLOGICAL SERVICES PTY LTD
_______________________________________________________________________________________
Gas Purge Operational Characteristics
In the foregoing, the discussion has been limited to static head conditions, whereas in practice,
the levels in stream are constantly fluctuating.
“Rising” Situations
It is the “rising” or “increasing head” situation that is critical for the correct operation system.
Consider a situation where the gas supply is cut off and the level rises- refer Fig.5.
Fig.5 - With gas supply cut off. Head increased from H1 to H2, gas is forced
down the tube by an amount X.
In this situation, it can be seen that whilst the system pressure has increased, it is not equal to
the new head H2, but rather H2-x. This condition will remain as long as the gas is shut off. In
other words, we now have a “closed” system, which respond to changes in accordance with
universal gas law-
a constant
PV
T
i
i
i
To revert back to the open system, we must restore gas supply, which will eventually build up
pressure in the system, until the gas escape from the orifice and the system pressure again
becomes the precise head measurement.
The time taken for the pressure system to respond to a given head pressure is commonly referred
to as “follow rate”. The normal procedure is to establish the maximum rate of rise to be
measured and adjust the gas flow so that there is no significant lag in the pressure system.
However, in order to conserve the gas supply, the flow rate (bubble rate) is set to the aluminium
that will meet these conditions.
Gas Purge Compressor
Issue 7:
16/12/03
© Copyright
HS55 110-017
