For 1/4-28 and 1/4” NPT PortsAlthough HPLC LAB SAFETY CAPS are available with built-in check valve elements, ventilation control valves may also be purchased as stand-alone units. With Air Inlet, Relief, and Reversible configurations, vent control valves may be selected in two cracking pressures and with Viton, EPDM, and FFKM seal materials. Air inlet valves permit air to enter a bottle to displace vacuum while solvent is pumped out to an instrument. Relief valves allow pressurized bottle contents to escape above the cracking pressure. Reversible valves may serve either purpose, air inlet or relief, depending on the orientation once installed.