  Gaseous detectors are widely used in high energy physics, and are attractive
choices in tracking systems for cosmic muon imaging, also called muography.
Such detectors offer high resolution and high efficiency at reasonable cost for
large sizes, however, one of the drawbacks is that the gaseous detection medium
must be prevented from contamination by outside air or internal outgassing.
Standard systems work with a constant gas flow, leading to regular maintenance
in the form of gas cylinder changes, which can be an issue for remote field
applications. In this paper we discuss the practical possibilities to reduce
gas consumption of an outdoor gaseous tracker, where particularly the gas
density change from daily temperature cycling limits the input flow. Such
"breathing" effect can be circumvented by well designed buffer volume, which
must prevent external air contamination. A realistic MWPC tracking test system
with 0.9 square meter area, total volume of 160 l, has been operated for 36
days with a flow of 3 l/day, confirming that the buffer volume, in this case a
50 m long and 10 l volume low diffusion tube, ensures sufficient gas quality.
The key effects governing the gas flow dynamics, including diffusion and gas
volume change, has been studied quantitatively, leading to practical design
prescriptions.
