This Pressure Relief Valve is designed to work specifically with separatory funnels. These pressure release valves reduce the hazards of pressure build-up. They simply slip over the drain of the funnel and tighten down with a twist of the wrist. The valve can be easily removed when it is time to drain the funnel. Each valve is made of PTFE resin and is factory preset to release at 1 psi of pressure. The valve can be adjusted to release at pressures up to 5 psi by turning the pressure release slug on the top of the valve with a screwdriver. The 7.5 to 9.5 mm sizes works with Glas-Col funnels from 60 to 1,000 mL in size and the 12.5 to 13.0 mm size works with the 2,000 mL funnel (item #21223). These also work on other manufacturer's funnels that have spouts with widths in these ranges.