Figure 9-28 Each of the two open scavenging interfaces requires an active disposal system. An open canister provides reservoir capacity. Gas enters the system at the top of the canister and travels through a narrow inner tube to the canister base. Gases are stored in the reservoir between breaths. Relief of positive and negative pressure is provided by holes in the top of the canister. A and B, The open interface shown in A differs somewhat from the one shown in B. The operator can regulate the vacuum by adjusting the vacuum control valve shown in B. APL, adjustable pressure limiting valve. (Adapted from Dorsch JA, Dorsch SE: Controlling trace gas levels. In Dorsch JA, Dorsch SE [eds]: Understanding Anesthesia Equipment, 4th ed. Baltimore, Williams & Wilkins, 1999, p 355.)