Hikari Check Valve. Avoid disaster! Water siphoning backwards through your aquarium airline can lead to BIG problems. Hikari can help you avoid them with ease. Cheap Insurance For Freshwater & Marine Aquariums Eliminates the chance of water siphoning backwards and damaging your pump or causing an electrical short High quality neoprene valve provides the ideal cracking pressure to reduce surging Easy to read directional arrow molded in durable plastic for easy flow direction confirmation Clear window allows function verification and visible signs when replacement is needed Two valves per package for about the price of one from our competitors 2 Pack