back flushing sounds

[boldstep]

Does anyone pay attention to the sound after ceasing back flushing? Sometimes it makes a little whooshing sound but other times it sounds really powerful. Is this any indication of how good a job it did in flushing the system? Should i push it a few times until i get a good one? :D Why does the sound change? Just curious...

[hlsheppard]

Good question. I've often wondered but have no idea...

[MDL]

I hear the same thing. My impression is that backflushing when there is air in the portafilter produces the loud noise (the air can compress and then makes the noise when it expands after the 3 way valve opens). If you unlock the portafilter to let some air in and then backflush the noise increases. I would not imagine that the noise reflects the efficacy or quality of the backflush action, but this is just a guess.
Mark

[boldstep]

An interesting and plausible explanation. My usual routine (when I am done making espressos for the day) is to take out the portafilter and scrub it with a brush and then insert it back in with the backflush disc inserted. It seems to me that any air that would exist in the portafilter would therefore be fairly constant. However, the noise it produces is different pretty much each time I backflush... ???

[caf4brains]

My first backflush is always the most dramatic and all subsequent ones in the same session are pretty calm. I assumed that all the air trapped in the p/f was released in the first flush. Liquid only backflushes would be quieter.

[blgros]

what if you filled the pf with water before backflushing?

[JohnB]

If you empty the drip tray & watch your backflushes drain you will find that the louder first flush contains more water, hence more noise. I dump the p/f each time I backflush with plain water as I figure the larger flushes are more effective for cleaning.