We have a 4 zone lawn irrigation system with the water intake coming from the canal. The intake pipe has a check valve and sits 18 inches deep in the water. That places the intake anywhere from 3-4 feet lower than any of the sprinkler heads. The length of pipe in the water is approximately 20 feet running along the edge of the seawall. The problem: The screened intake and at times 15 feet of the pipe has been found to be "floating" on top of the water. This might repeat every 10-14 days, even though the system has been running without problems in all 4 zones the day prior. This started 8 weeks ago in the system which has been in place for over 4.5 years. The company said that the problem was the Aquasleeve material on the intake pipe reducing pressure, or the check valve must be failing- somehow allowing the water to drain out of the system, hence the intake pipe eventually filling with air and floating to the surface. 4 weeks ago a small leak at the elbow where the pipe rises from the water at the level of the seawall was repaired. At that time the check valve was found to be OK and a new piece of Aqua Sleeve was placed (it gets brushed at least once each week). Yesterday the pipe was up on the surface again. I said that the water would seek its own level and that even with a "leak" in the system, the water would not passively be displaced by the air, especially 2 feet under water. HELP, please.