Hey guys ... I built a system in my 2.2acre pond recently with your help on this forum .. seemed pretty straight forward as I built a similar system on my other pond which is working fine ... the system is running over 20 psi and I can’t figure out why here is the setup ....
Pump is a gast 0823 ....this pumps air into a 1.25” black poly line laying on top of the ground along pond edge... the first tee into the pond is 100’ from pump and has a gate valve that goes to a 5/8 line 80’ long out to the deepest diffuser which is a double vertex in about 14’.... the next tee is another 100’ down the main line and has a gate valve which sends another 80’ 5/8 line out to another double vertex diffuser about 13’ deep... the next gate valve and tee is 50’ more feet down main line(250’from pump) .. this one goes about 125’ out and is about 9’ deep and is a single vertex diffuser .. the last gate valve is at the end of the 1.25” main line(325’ from pump) and a gate valve sends another 5/8 line out about 50’ To the final vertex about 8’ deep
The weird thing is I have unhooked the mainline where it goes into my pump house and had water shoot back out from the backpressure ... I’ve also swore I’ve heard water in the mainline near that first gate valve ... I can not figure it out .. it almost seems the the air moving to the other diffusers is siphoning the water back from the deepest diffuser set .. I know there’s a check valve in the vertex’s but maybe something broke on its way to the bottom I dont know but I am stumped any help would be appreciated!! Thanks

According to the Gast 0823 pump curve, it's suggested max pressure is 10 psi...



I know they will handle more, but I think your right...something is wrong. My Gast 0523 also has a 10 psi max and I have pushed it to 20 psi once to perform amperage tests. It starts fluttering and making obviously bad noises. If your diffusers all look to be operating well, I would suspect a bad pressure gage. Can you cross check the pressure gage, maybe swap gages from your other system? What is the pressure range of the actual gage. Many wide range gages are not very accurate at the low end. A 0-30 psi gage would be a good choice and liquid filled would be good to better handle the rapid pressure fluctuations from the pump.

I don't see anything obvious with your design unless your gate valves are causing restrictions, but your diffusers would be performing poorly I would think.

Your pump house must be very close to the same elevation as the pond surface for water to flow back up the mainline. It sure seems odd that a diffuser (even one without a check valve) would allow enough backwards flow to push it very far uphill. That is very odd because the actual slitted diaphragm acts a lot like a check valve...certainly a flow restriction.

Condensation in the air line maybe?

+1 on condensation.
Ideally, you would have the line running downhill the whole way, from pump to pond.
A low spot in the path would make sort of a J-trap. If that's the case, you might want to fix it before winter and it freezes.