Hikari USA Inc. - Check Valve 2Pk. Aquarium: Water Valves & Bulkheads For use with freshwater or marine aquariums. Eliminates the chance of water siphoning backwards through your airline and damaging your pump or causing an electrical short. This high quality neoprene valve provides the ideal cracking pressure to reduce surging and provide a long life. Easy to read directional arrow molded in durable plastic for permanent assistance with flow direction. Clear window allows function verification and visible signs that replacement is necessary. Two valves per package. 2 Pk