Randy: Mostly correct: The pump is external so from the supply throught the filter/regulator to the pump and then to the machine. I just went through the L.M. manual and unless I missed it they don't spec out the supply pressure. I ran the Astoria for 15 years on line pressure (80-90lbs) with no obvious troubles. I think what has caused the pressure spikes I wanted to troubleshoot in the O.P. is a check valve not sealing. Is that a check valve on the pump outlet? I think I've found that answer at EPNW, they list a check valve that goes on the pump outlet. I've got to get my tools and remove and "check" out that check valve. Might get a replacement first to avoid taking it apart twice. While I'm at it might look for an industrial valve; Oh heavy duty-ism will be my downfall!
Duke

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I ran the Astoria for 15 years on line pressure (80-90lbs) with no obvious troubles.

Consider yourself very, very fortunate. Average line pressure (city mains) in the US is around 70 psi. Typical recommendations from plumbing supply houses are 50 psi so as to not overburden household fixtures. Typical recommendations(?) from individuals desiring a hot firehose shower in the morning are around 100 psi.

Unique amoungst manufacturers, LM specifically reverses the install direction of their stm boiler fill valve to reduce the potentials of high line pressure - see this: http://www.lamarzoccousa.com/LM%20USA/d ... tation.pdf

Brew boiler pressure is essentially meaningless at any time other than when water is flowing. I do believe you are chasing a problem that does not exist.