While racking beer to kegs today, my autosiphon started leaking air. Bubbles started at the bottom, and went throughout the tube. I assume that this is due to a poor seal between the pump portion and the housing portion of the stiff plastic pump. Has anyone else had this experience? Is this a common failure mode for autosiphons?
It sounds like your auto-siphon is not making a good seal between the main cylindrical body and the gasket at the bottom of the siphon tube. This may be due to debris on the rubber gasket, which would mean a cleaning could get you back in order.
- Completely remove the inner siphon tube from the main body by pulling the tube up, out of the top.
- Examine/clean the seal, which is typically a black rubber 'ring' at the bottom of the siphon tube. You might put a small bit of keg lube on it, if you have it.
If the seal is beyond repair, you might be able to find a replacement seal, but my quick search a few moments ago didn't turn up a good result. I'll come back and edit this if someone finds one.
While the unit is taken apart, look for hairline fractures in the siphon tube. If that's the problem, you can buy a replacement siphon tube with new seal (rather than the entirely new auto-siphon). I found this example.
There is also the possibility that what you're seeing is not air being pulled-in through a leak in the gasket or a crack, but indeed just CO2 that's coming out of solution due to a disturbance (credit @brewchez for this idea). I'd look really closely at where those bubbles originate!
I've gone through 3 of these, and at least one failed because of the leaky gasket.
It often happens when the cane is pulled out of the housing quite far, and the cane is not in the same line as the main body. See if pushing the cane back into the main body helps, since it's then a lot harder to move the cane out of alignment.
If its a leaky seal its a leaky seal, but I'll offer a different perspective when I thought I had the same problem.
I find that I actually get some "cavitation" in the siphon that I think is from dissolved CO2 coming out of solution. I used to have the bigger bore autosiphon, and that issue went away with a more normal 3/8th inch autosiphon. So you might not have a leak it could just be a build of of CO2 coming out of solution.
If you don't want to buy a new siphon you can try and lessen the strength of the "pull" to limit the turbulence that leads to cavitation. If its pulling to hard you may want to adjust the height differential between the two vessles being transferred.