Curiosity question about pvc overflow

[Sean5545]

Hello everyone,

I have a quick 2 questions that I have been wondering about for quite some time. What is the purpose of the air vent on a PVC overflow and why is it recommended you do not have a throttling valve on the siphon side? I ask because I ran my system for two years with both and didnt seem to have any issues. I've just changed it a bit to make it a little safer for small fish and I added the air vent (granted mine is only an 1/8 hole in a pvc cap....couldn't get enough flow wide open on air). I still have the gate valve on the siphon side to adjust flow, the pump side is unrestricted.

Thanks in advance

Sean

 

[pisanoal]

I think you are mistaken on the "don't have a throttling valve on the siphon side". The general rule is not to have one on the non-siphon drains if we are speaking beananimal. The design is such that a throttling valve on the siphon controls the flow and keeps that drain at full siphon while allowing just a little bit to overflow the trickle drain. It would be unwise to throttle the trickle drain, because if your siphon were to clog, you run the risk of your trickle drain not being able to handle all of your flow. Of course if you are running a 3 standpipe system, that isn't a big deal either as your emergency will become the trickle. The emergency should definitely remain full bore.

I believe the hole in the top of the trickle drain is just to allow air to move freely in that drain although i haven't found it necessary. Maybe my system would start-up/run a little smoother with it, but its hard to imagine it making much of a difference as it runs really smooth right now.