I'm quite interested to check how accurate the pressure gauge in my Duetto is, and perhaps adjust the brew pressure a bit more accurately. I've read through all the threads I can find about PF pressure gauge adapters, and constructing one seems fairly straightforward.

My original Izzo PFs have a nice thread to attach a fitting. Unfortunately, I haven't been able to find a suitable pressure gauge at any of the typical sources. All the hardware stores I tried either have 0-100psi gauges, or 5000psi+ gauges for pressure washers. I think I will probably end up ordering a fluid-filled gauge from Cole Palmer. $30 is a little more than I was hoping to spend, but no big deal.

An important detail I'm unsure about is whether I need to add some sort of water diversion valve. Some people say it's absolutely necessary to draw a normal shot flow to get an accurate reading, while many others are obviously (from photos) using straight adapters without this feature. I'd like to sort this out before ordering anything, because it will presumably affect what I choose: a rear or top connection gauge, for instance. Any thoughts?

Did you check Google, Chris? This top hit FAQ thread with virtually the same subject as yours covers the topic in a lot of detail, IIRC, with many, many examples for inspiration.

Yes, I did read quite a number of threads on the subject, but didn't realize it had been conclusively determined that a PF pressure gauge must have a flow simulator to be worth using. In almost every thread I read, most people have extremely basic adapters, and there is debate over whether it's even worth adding something to simulate shot flow. Even in the thread you linked, Greg Scace says the error is a lot more significant on a vibe machine, which I don't have. From what I read even before posting my own thread, it seemed like I should probably have a flow simulator, but I was just hoping to get some confirmation on the subject.

I was also going to ask if I should buy a 0-200 or 0-300psi gauge...

You might want to check AutoParts stores. One close to me has a couple different liquid filled gauges which would work for a PF setup. Just a thought.

I would buy a gauge that gives you small enough reading thats allows you to fine-tune your pressure. For example, you wouldn't want a brew pressure gauge that read from 1-30BAR(for example), in /5BAR increments.. Ideally, you would want one which read to like a max of 20BAR, but with .1 or .2 increments. I believe your machine reads up to 16BAR, in .2 increments, so maybe try and find something as close to that as you can find.

I dont think it matters what it's max reading is, within reason, as long as the increments are small enough for you to make accurate adjustments. I would think 0.25 increments would be the max(so you would have 3 "notches" between whole numbers)

Bob_McBob wrote:From what I read even before posting my own thread, it seemed like I should probably have a flow simulator, but I was just hoping to get some confirmation on the subject.

You won't find a definitive answer since the type of pump matters, the presence (or absence) of gicluers matters, and the presence (or absence) of a pressure-shunting OPV matters, to name only three possibilities. Many rotary pumps have a bypass valve that is not entirely insensitive to the flow rate (or lack thereof), while others have a "balanced" bypass valve that delivers the same discharge pressure independent of inlet pressure.

In my experience, the reading from a DIY pressurized portafilter on a rotary-pump equipped espresso machine without a discharge valve is pretty damn close to the more-accurate-than-most-need Scace II. In a pinch, I've simply loosened the gauge fitting so it drips and that's been enough to get an accurate, stable reading. Besides, for our purpose, the delta is more interesting than an absolute measurement (i.e., "How does the taste profile change if I increase pressure by 1 bar?"). Guys like Greg Scace and the WBC are worried about calibrating equipment to an agreed-upon standard, not the adhoc tweaking we engage in.

Bravo H-B!
Tweaking is fun but O.C.D. is rampant and expensive!
-Richard / espressme

I am all about rampant experimentation for the fun of it but I sure love the expensive OCD techniques as well. IMHO if you are going to build the DIY pressure gauge you might as well add the T and needle valve... that way you can check both... Go OCD!

Bob_McBob wrote:...An important detail I'm unsure about is whether I need to add some sort of water diversion valve. Some people say it's absolutely necessary to draw a normal shot flow to get an accurate reading, while many others are obviously (from photos) using straight adapters without this feature. I'd like to sort this out before ordering anything, because it will presumably affect what I choose: a rear or top connection gauge, for instance. Any thoughts?

I'm not recommending this as an OSHA-approved technique - on the other hand I have done this myself. A low-budget way to get the valve you want to get the flow you want is simply loosen the pressure gauge on the threads till your leakage is at the rate you need (shot glass and timer). The pressure on the gauge puts a force on the threads, which combined with friction, prevents unassisted motion (assuming you haven't lubricated the threads with some super lubricant). In my case the gauge does not back off. If you're a safety freak, or you've got slippery threads, you could keep a finger on the gauge to prevent the start of any motion. Unlike the coffee puck, where your area gets you around 500 pounds of force, your gauge is hooked to a small opening where the downward force is on the order of 10 pounds. Consider the 50:1 (or so) ratio you get in the threads, and the 1 or 2-inch lever you get at the body of the gauge, and you only need a few ounces of force to counter any backdriving, and that's if you had no friction in the threads.

A slightly different topic: most low-cost gauges have no calibration info nor temperature-compensation info, and probably no temperature compensation. The gauge itself will warm up as you tweak your set-up. A reasonable check, once you've got your flow rate tweaked and got your pressure reading, is to let the gauge cool down to ambient, leaving the set-up undisturbed, and then get another pressure reading.

-Ed

A picture.

Some iteration is needed for most schemes... get the flow, measure the pressure, adjust the pressure, adjust the flow, repeat, etc.

And on the topic of instrumentation on the cheap, a Scace-like temperature measurement that uses an ESE pod for the pressure restricter (flow control):

Just a 1/16" hole, a TC, a drop of silicone caulk, and a bottomless portafilter.
Flow control is done by how many uses the pod gets. Usually for me the first use is too slow, and the sixth is too fast. That old variety pack from years back can finally get some use.

-Ed

Nice use of that ESE pod for a flow restriction. I am glad someone has found a way to dispose of them that has some value.