smasha Senior Member Joined: 19 Feb 2012 Posts: 32 Location: Cambridge Expertise: I love coffee
Posted Sun Nov 18, 2012, 10:38am Subject: viebemme pressure issues
at work we have a viebemme HX machine with vibration pump. often when pulling a shot the pressure gauge can read 5-7 bar other times it goes well over 12 bar and jumps up to 15 and back down to 12 bar.
I thought most HX machines are meant to pump at a constant 8-10 bar and grind and tamp effect flow time and the aim is for a 25 second flow for a double shot with 14 g or so of fresh ground coffee.
so I assume there is something wrong with this machine and that is probably the vibration pump or possibly the pressure gauge. comments or suggestions of how to find the cause and plan for repair will be very useful!
Posted Sun Nov 18, 2012, 11:34am Subject: Re: viebemme pressure issues
Likely there is nothing wrong with the pump if it can deliver 15 bar. The problem is likely in the pressure relief valve. if it was working before properly and recently started doing this, it probably has the correct spring in it, so all that may be needed is to remove the adjustment screw, spring, and piston, clean as necessary, lube with DOW111 and reassemble and adjust.
SStones Senior Member Joined: 24 Nov 2012 Posts: 369 Location: Canada Expertise: Professional
Espresso: Giga 5, ECM Giotto, Rocket... Grinder: Anfim Milano-Best Vac Pot: No :( Drip: Some $30 thing from Walmart Roaster: I buy pre-roasted.
Posted Sun Nov 25, 2012, 6:21pm Subject: Re: viebemme pressure issues
The pump can't control the pressure, it just creates flow. If your grinds are loosely tamped or too coarse, the water will run through them easily and the brew pressure will be very low. Pressure rises due to your espresso grinds restricting the flow. I would adjust the relief valve (OPV in these forums) to limit the maximum to about 10 bar for your pump's safety, and see if you get a steady 9 bar +20 second pull on a finely ground, evenly tamped double espresso.
what I am confused about the issue on pressure is at home my rocket with a rotary pump produces a constant 9 bar of pressure. If the grind is too fine and tamp too firm then the time taken is > 30 seconds for a double shot. If the grind too coarse and tamp too light the time taken is < 15 seconds. So to get a perfect brew I adjust grind and tamp top achieve a 25 second brew time. In all situations the brew pressure is fixed at 9 bar.
the veibemme at work with a vibration pump varies the pressure dependent grind and tamp; sometimes the pressure is low at 6 bar, sometimes it is high at 14+ bar.
So is this difference that I have observed the difference between vibration and rotary pump? or is something wrong with the veibemme vibration pump?
what I am confused about the issue on pressure is at home my rocket with a rotary pump produces a constant 9 bar of pressure. If the grind is too fine and tamp too firm then the time taken is > 30 seconds for a double shot. If the grind too coarse and tamp too light the time taken is < 15 seconds. So to get a perfect brew I adjust grind and tamp to achieve a 25 second brew time. In all situations the brew pressure is fixed at 9 bar.
This is because the pressure is taken from the pump head within the sealed brew circuit and the flow of the pump is so great that even with no portafilter in you will see a pressure of 9 bar. The size of the gicleur within the E61 group (0.6 mm possibly larger on your machine) is so small that a rotary pumps flow will always show at 9 bar (or whatever pressure you have set the pump to) because of the restriction.
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