Re: Pull shot.. great! Pull next shot.. whoooa waterfalls ahead!
Would definitely be contributing to the problem Simon.....
Typically, with a decent double basket fitted (NO Coffee), the resistance to water flow will raise the pressure to ~3 BAR at the Group Head. It is only reasonable to assume that increasing the size of some of these holes will allow for increased flow and thereby decrease the pressure at the Group Head. Another effect would be, that if the holes are even slightly grouped together, to encourage channelling within the proximity of the larger holes and lead to early blonding due to poor extraction of the coffee at this site.
A "Rule of Thumb" relating to Water Flow... For every 50% increase in diameter of an orifice, the Water Flow Rate will Double at the same Delivery Pressure. Conversely, for every 50% increase in the size of an orifice where the Flow Rate remains the same, the Delivery Pressure will be Halved.
Even though the Coffee Cake provides the majority of resistance to Water Flow, the Basket Holes also do their bit....
Mal.
Originally posted by 3E242022233E26753F4D0 link=1275978291/13#13 date=1276943178
Typically, with a decent double basket fitted (NO Coffee), the resistance to water flow will raise the pressure to ~3 BAR at the Group Head. It is only reasonable to assume that increasing the size of some of these holes will allow for increased flow and thereby decrease the pressure at the Group Head. Another effect would be, that if the holes are even slightly grouped together, to encourage channelling within the proximity of the larger holes and lead to early blonding due to poor extraction of the coffee at this site.
A "Rule of Thumb" relating to Water Flow... For every 50% increase in diameter of an orifice, the Water Flow Rate will Double at the same Delivery Pressure. Conversely, for every 50% increase in the size of an orifice where the Flow Rate remains the same, the Delivery Pressure will be Halved.
Even though the Coffee Cake provides the majority of resistance to Water Flow, the Basket Holes also do their bit....

Mal.

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