Omniswivel check valves only allow gas to flow in one direction and are open against upstream gas flow inlet pressures exceeding 1 psi. In the event of complete loss of gas flow pressure a check valve will automatically close. The Omniswivel system check valves are typically used to protect against water entering the second stage and being inhaled in the event of loss of gas flow due to inadvertent disconnection or a severed upstream hose. We do not recommend use of check valves in the circumstances of most recreational diving applications.