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[FrankJ]

As for valves, we used this: Asco 8353C035. It is a high flow air valve designed for back pulsing filters.

As to the PCV. Pressure is pressure. But PVC (the kind they use in for pipe) is brittle. When liquids decompress, they don't expand like gases do, so liquids don't throw shrapnel the same way air does when the pipe shatters. The density of air is so small & the distances involved are small so you do not get significant pressure spikes from "water hammer"

The PVC is not going to randomly burst under normal conditions, with air or water. But if it does, maybe it gets bumped in the wrong way, something hits it, etc, it has a bad failure mode. Well documented. Big legal liability. Especially for any mentors on the team that are registered professional engineers. Makes the cost for other material seem small.