bubbles in my herms line

[Tinga]

I've been using my herms set up now for a couple different batches and I seem to keep having the problem where bubbles get introduced in the line and my flow out of the coil is lacking.

so I have my mash tun well above the pump and the coil in my hlt so there are no problems priming the pump or the coil. I generally open the ball valve from the mash tun and let it flow through the pump and the coil and I can see that there is wort coming out of the coil. that is when I turn the pump on. So I don't think it's a pump problem.

the only thing I can think of is that the grain bed is getting compressed and isn't letting enough wort through. But I'm still confused as to how the air bubbles are getting in the line. if the grain bed didn't let enough wort through wouldn't it just create a vacuum and the wouldn't be any bubbles?

this is a problem because although I'm getting a very small flow out the end it isn't enough to fill the tube where the temp probe is so I don't know if I'm getting an accurate temp reading and I don't get enough flow to keep the temperature in the mash tun where I want it.

 

[Rivenin]

did you do plumbers tape on all threaded fittings?
is the tubing clamped into place?

 

[skipper1953]

The only thing I can think of is that the grain bed is getting compressed and isn't letting enough wort through. But I'm still confused as to how the air bubbles are getting in the line. if the grain bed didn't let enough wort through wouldn't it just create a vacuum and the wouldn't be any bubbles?

If this is actually what is happening, then you are likely pulling gases out of solution and forming bubbles. It is basically the same principle as using a vacuum to de-gas wine. The hotter the liquid, the more easily the disolved gases are drawn out of the solution. If you're using a centrifugal pump, this causes cavitation and further reduced flow rates. Try throttling back on the outlet side of your pump to balance the system and eliminate cavitation. This will help to avoid compressing the grain bed. There are ways of creating a more free flowing grain bed to start with, if necessary.

I would check for air leaks in the plumbing between the grain bed and the pump. Whether I found any leaks or not, I would take steps to throttle the output of the pump.