As a tank depletes with a single stage regulator, what occurs?

• A. Outlet pressure rises
• B. Outlet pressure stays the same
• C. Outlet pressure falls
• D. Pressure fluctuates

Answer: (A)

With a single-stage regulator, the goal is to deliver a set downstream pressure by balancing the spring force against the incoming gas pressure on the diaphragm. When the tank is full, the regulator can hold that preset outlet pressure. As the tank depletes, the inlet pressure drops. The regulator can usually maintain the same outlet pressure only while there is enough input pressure; once the inlet pressure gets too low, it can no longer sustain the set downstream pressure, and the outlet pressure falls. You might also see some fluctuation if the demand changes or the input pressure nears the regulator’s minimum operating pressure. So, as the tank empties, the outlet pressure tends to decrease rather than increase, with possible fluctuations near the end.