The ProboFlow controls the pressure and flow of one gas to a process device, e.g. a ProboStat measurement cell, and optionally receives return gas. The gas supplied to the device is split in two parallel lines, and the return gas receives two gas lines that are collected and routed to a common ventilation outlet. The unit has a pressure reduction control valve, and in addition an internal safety overpressure relief valve before the output to the process device. This opens at 0.7-1.0 bar overpressure and the overflow gas is routed to a separate ventilation outlet. Normal safe use implies setting a small operation overpressure of 0.2 - 0.5 bar at the reduction valve. Moreover, one should use the stop valve to allow or deny flow, regulating and reading the flow at the flowmeter. By proper normal use one avoids any dangerous overpressure to reach the process device.