here is a quick down and dirtay MS Paint on how I plan on using my air vent.
Is this going to work for me?
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-=Jason=-
The autovents in BeerThirty's rig were placed above the pumps with enough tubing to catch the air bubble from the keg dip tube. When the pump is started the bubble hits the inlet side first and most will vent if the pump is stopped for about 15 seconds, the remaining air usually will pass on out through the outlet air vent. The plastic tubing connecting them to the pumps is 1/2" PFA that was heated and formed into the bends to keep the stress on the pump connections minimal. if you were to build a "D" loop on its back with the flow along the bottom and the air vent in the top, you might be able to catch the air bubble and vent it.
It would seem to me that once an air bubble makes it past the pump head it would make no difference where it goes. It may exit through the autovent or it may move on to where the tubing terminates. Once the pump head is flooded and no air remains downstream on the suction side of the pump, there should be no further priming problems unless there's an air leak. I would think that the autovent would permit the pump head to be flooded with ease, then you could turn on the pump and push out any air that in front of the pump.
So you're basically saying I should put the air vent on the inlet side of the pump to allow air that blocks the pump head from flooding the release.
My understanding is that this is one issue. The second issue is that when you turn off your pump, air can be pulled back into the pump head, causing it to lock up on you. Hence the need for two autovents.
I'm not sure where the best spot to position the vents are, though. Close to the pump? Near the keggle? Up high? I even thought of having them on a quick connect I could move around.
I'm going to try having a vent on the inlet side as well as the outlet.
Absolutely NO. The vent must be on the output side of the pump.
Here's my take:
1. You can avoid the possibility of pulling air back into the pump head by simply closing the flow control valve on the output side of the pump before turning off the pump.
2. Raise your kettle some or lower the pump. You need a little bit more positive suction head in order to make priming easier. This would very extremely easy to try, so why not do it?
3. You only need a single vent (auto or manual) on the output side of the pump.
I have one on the inlet of each pump to allow priming when the pump cavity is full but the line is empty, and one on the outlet of each pump so when the pump is turned off air that is trapped in the outlet lines or valves cant flow back to the pump and vapor lock the pump.
I understand what you're saying. #1 makes sense to prevent air being pulled back. However, according to Beerthirty, the vent that was to relieve air pressure pulled back was on the OUTLET side.
Closing the valve on the ouput side (the flow control valve) would prevent ANY air from being pulled back into the pump head. Close this valve BEFORE turning off the pump.
My problem really does appear to be lack of positive pressure from the keggle. I see the air bubbles get trapped in the tube from keggle to pump. But raising it is an issue due to hard plumbing I have to gravity transfer from my mash tun above it. It's as high as it can go to allow transfer. If I raise it, it'll be above my mash tun plumbing, among other challenges. I might be able to lower the pump a bit, but not much.
It appears from the pics that you have a flexible tubing (not hard piping) from the kettle to the QD which should allow you to raise the kettle very easily.
If the problem is air stuck in the dip tube, wouldn't a vent on the inlet side solve this problem?
IMO, this should not be necessary.
Secondly, If I drilled a small hole or two in the dip tube, would it keep air out of it and still suction fine? I use a hop strainger so hops aren't really an issue.
This would also not be necessary so long as you have enough positive suction head which can be accomplished by raising the kettle some. You could also try removing the dip tube entirely and re-test. IOW, temporarily remove the DIP tube from the equation.
Thanks again for all the ideas. There do seem to be some conflicting concepts about setup of this thing.
If I drilled a small hole or two in the dip tube, would it keep air out of it and still suction fine? I use a hop strainger so hops aren't really an issue.