Analog (mechanical) pressure gauge for a single cylinder filter

Summary
How can I put a pressure gauge on a metal cylinder while maintaining vacuum, using only a lathe and/or a bench drill?
These guys made a manual espresso machine and specify using 30 lb of pressure in the manual. In order to determine the correct pressure, they literally tell the user to push down on a kitchen scale. I'm considering a competing product, and that seemed like a rather obvious oversight. Surely there's an economical analog pressure gauge on the market that can be attached to the assembly? For instance, a cheap blood pressure monitor costs ~$35. Surely it's sufficiently accurate?

Now, the system I have in mind uses a cylinder that may or may not have pre-attached valves. Assuming even the predrilled valve is the right size, how do I attach such a gauge without compromising working pressure and volume? If there is no valve (a solid cylinder) do I have any way to attach one using only a lathe and/or drill press (ie no welding)?

Many thanks in advance

Joe
 

Baluncore

Science Advisor
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Welcome to PF.

Gauges are usually threaded. Adaptors are available for any thread. You could drill the metal, then cut a thread into the hole, or connect the gauge to an existing port.

Rather than measuring the strain in the handle for display, you could make a flexible handle with a pointer, like an indicating torque wrench.

It takes about 14.5 pounds to pull a vacuum in a one square inch cylinder, (atmospheric pressure). If you came up with a two square inch sealed cylinder you could push it down once to create the vacuum, then relax while the fixed 29 lbs pressed the coffee through the filter.
 

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