any advise on the pressure of a la pavoni which is 9 vs the pressure of some other machines that can be say 15. does that mean that a la pavoni manual is not as good at extracting. vs the ones that are 15????
The pump pressure rating is more of a marketing scam than anything. Proper espresso is best extracted around 9 bars (130psi or so). Anything over that is just overkill as it's not used anyway. Most machines that use pumps have some sort of OPV (over pressure valve) that vents anything much over 9 bars back into the water tank or possibly even into the drip tray.
Say a pump is capable of cranking out 15 bars and you only need 9 to get the job done. That's where proper dosing, distribution, tamping, etc. comes into play. Basically you're using those factors to slow the flow down to 9 bars for proper extraction. Later!