What must be provided downstream of each pressure switch and mainline gauge?

In the context of medical gas systems, it is essential to maintain proper pressure regulation and safety features to ensure consistent delivery of medical gases. The correct answer focuses on the necessity of providing a demand check fitting downstream of each pressure switch and mainline gauge.

A demand check fitting is crucial in this scenario because it serves as a safeguard against backflow and contamination. This fitting allows for the unidirectional flow of gas, ensuring that gases intended for use within a healthcare facility do not flow back into the mainlines or other delivery systems in case of fluctuations in pressure or during equipment maintenance.

This measure is particularly important in medical gas systems, where purity and safety are paramount. It helps protect the integrity of the gas supply and the health of patients and personnel by preventing unwanted gases from entering the system, which could potentially cause adverse health effects.

Additionally, this fitting is designed to respond to changes in demand for gas, allowing supplies to adjust but keeping the lines secure from any reverse flow. Such safeguards play a vital role in the reliability and safety of medical gas systems, which are used extensively in hospitals and other medical settings.