Posted Fri Jan 22, 2010, 5:15pm Subject: flow rate: is there something wrong here?
Hi Everyone, I've been having a bit of trouble getting good espresso lately and I've worked a lot on my technique etc but I'm starting to think there might be something wrong with my machine and I've started to suspect the pump. I have a Bezzera BZ-40P with a procon rotary pump. With the little bit of confused searching I did I realized that my flow rate seems to be really high. I put a measuring pint glass below the group (no PF) and hit the brew button and I got:
350 ml (12 oz) in about 17 seconds
That's almost a full pint glass and a flow rate of 20.5 ml per second. Admittedly, I'm still trying to understand espresso machine mechanics, but that sounds pretty high to me. My machine has a pressure gauge, which i have set at 9 bar although without resistance, it measures about 8.5 bar. Is this a sign of a problematic pump or is there a flow restriction valve that is either broken or not set right?
Does anyone else have such a high flow rate and is that normal? Also, I'm not sure if this makes a difference, the machine is meant to be plumbed in but I put the hose in a water reservoir that I fill with filtered water. Thought I'd mention that in case it might contribute to pump problems. Thanks for your help!
ethorson Senior Member Joined: 4 May 2009 Posts: 50 Location: Port Townsend Expertise: Just starting
Espresso: Bunn ES-1A, Bezzera BZ35 Grinder: Mazzer Mini Roaster: Homemade
Posted Fri Jan 22, 2010, 8:48pm Subject: Re: flow rate: is there something wrong here?
My Bezzera BZ35 with a rotary pump flows about 16 oz in 25 seconds without the portafilter, which is roughly equivalent to your machine. I also use an external water container instead of a plumbed-in connection. The flow during extraction is much less due to the resistance of the puck and can range from zero to gushing depending on the grind. It does seem that this machine is very sensitive to the grind, dosing, and tamping since it does not have preinfusion. Sometimes the shot will start with a little spurt, choke up as the puck expands, then start to flow again.
The BZ35 has a very small heat exchanger and I have had better luck getting good extraction by skipping the "HX cooling flush" altogether. Unlike an E61 machine, the group is heated by conduction and tends to run a little cool. The overheated water from the small heat exchanger just compensates for the cool group to get close to the proper brew temperature. For some reason there is a slower rise in extraction pressure with this method that seems to produce more normal looking shots. I did have to turn the boiler pressure down a bit get the extraction temperature at 200F.
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