The Pentair U9-229 Cover O Ring is a replacement O-Ring designed for trap covers in Pentair JWPA and JWP above ground series pool and spa 1/2 3/4 1 and 1-1/2 HP pump models. This O-Ring prevents air suction and spitting back into the pool that can be caused by a swollen or cracked O-Ring. Regularly replacing O-Rings is crucial to prevent damage to your pool pump system.