If it is susceptible to contamination, such as reacting with moisture, the interior of the MFC may be polished and the connections changed from screwed or compressed fitting to higher purity type connections such as VCR or VCO which utilize metal seals and are considered when high and ultra high purity gases are being used.

If the process is being run at a positive pressure, the design of the MFC is such that it can contain that pressure. Some MFCs are limited to 100 psi or 500 psi maximum working pressures. Industrial MFCs are usually standard at 1500 psi (100 bar) and can be made to withstand 4500 psi (300 bar) pressure sometimes found in catalyst research, hydrogenation of food or drugs, or many petrochemical processes.

On the other hand, if your process operates under vacuum, the design of the MFC has to be adjusted accordingly. Gases behave differently at positive pressures than they do under high vacuum and calibrating an MFC for vacuum service is a precise process.

Temperatures of the gases are to be considered. Usually the gases are measured and controlled at relatively mild temperatures and elevated after the MFC if high temperatures are required in the process. There are temperature limits inside an MFC due to the measuring technology which utilizes the thermal properties of the gas to determine the flow. So, typically, 140-160°F is the working limit for gasses in MFCs.