Abstract: A coupler (for coupling a plug with a gas supply) may include a body having a first through hole and a second through hole. The coupler may further include a ring having a first cavity and a second cavity. The first cavity may be pneumatically disconnected from the second through hole when the ring is disposed at a first position with respect to the body. The first cavity may be pneumatically connected to both the first through hole and the second through hole when the ring is disposed at a second position with respect to the body. The second cavity may be pneumatically connected to the second through hole when the ring is disposed at the first position with respect to the body. The second cavity may be pneumatically disconnected from the second through hole when the ring is disposed at the second position with respect to the body.