The COM-1 Series crossover manifold system consists of two PR-1-type stainless steel regulators (PR-2-type brass, optional) mounted on a panel-mounting-type bracket shown with optional gauges. The primary regulator, supplied with a tamper-proof nut, is set at an outlet operating pressure at least 15 psig higher than the secondary regulator (supplied with a standard adjusting knob). As the primary supply source depletes and the operating outlet pressure of the primary regulator falls below the preset operating pressure of the secondary regulator, the secondary regulator takes over. Once this occurs, the secondary regulator can be manually adjusted 1⁄8-turn clockwise, the secondary regulator is now the primary and the depleted supply source can be replaced.