The restrictor is placed on the pop-off valve exhaust port and the scavenge tubing is attached to the other end. The button on the device top is depressed to close the exhaust, thus allowing the bagging of the animal. The restrictor allows the anesthetist to leave the pop-off valve open, but the animal still may be bagged when necessary. This prevents the chance that the pop-off valve may be left accidently closed, a situation which causes high pressure within the system, and can lead to respiratory damage and pneumothorax. Made from Delran, a sturdy, durable material.