PID'ing Olympia Cremina
a new idea...I think.
For some time now I've been pondering the challenges of using a PID on lever machines. The most obvious and troublesome is the lack of boiler pressure needed to prime the cylinder.
I was encouraged to see Raj's version in "Positive pressure, PID Pavoni: world domination begins", but I wanted to do something a little different. The main issues that I wanted to resolve were thermal instability caused by the introduction of unheated water, and lever resistance.
The idea for my system is to use air pressure instead of water pressure. I've seen some folks toy with the idea of using a bicycle pump, but I was looking for a more "elegant" solution. That caused me to begin a quest to find the appropriate miniature pump or compressor that might do the job. I quickly found that there are many choices for such a pump available for differing industrial needs and selecting the appropriate type and size of such a pump was a bit beyond my abilities. What I did then was to try to think of a more common type of pump that I may have seen before in my day-to-day experience. There were several that came to mind, but the most promising was the type of pump that is usually found in an automatic blood pressure machine, the type that typically sells for about $40 at the local pharmacy. I didn't want to actually pay for it since there was a possibility that it may not work at all so I asked a friend who is closely associated with the medical community if he might know of a source. It turned out he had a "barely used" machine that gave very inaccurate results for monitoring blood pressure. The store wouldn't refund his money so he gave it to me.
Here is a picture of the box:
I pulled the thing apart and it yielded a very small pump (or is it a compressor?....I don't know). It runs on 4 AA batteries or 6 volts.
This is a photo of the pump:
The first thing I needed to do was to determine if it would be capable of at least 1 bar to pressurize the boiler. 1 bar is roughly 15 psi so I went to the garage and scrounged some small fittings that came with a vacuum pump that I purchased for bleeding the brake lines on my car and a pressure gauge. I made an adapter from two cone shaped fittings put together with a small peice of tubing to hold them together and plugged the output of the pump into the pressure gauge via the adapter I made.
Here's what the setup looked like:
I hooked up the batteries to the pump and read the gauge. I was ecstatic! It read 19.5 psi!
Now I wanted to see what would happen when I pressurize the boiler using the pump. Another fortunate circumstance allowed me to do this with ease. My lowly Olympia Cremina is not in possession of it's original phenolic knob affixed to the boiler cap, but only has the brass cap which contains a one-way valve designed to allow air into the boiler after use when the machine cools down. It's a check-valve installed in a VERY convenient place. The missing phenolic works to my advantage here... and the little cone shaped adapter I used for my pump test fitted beautifully into the tiny hole. I inserted it, and with the Cremina turned-off, I pumped up the boiler and waited for the familiar click of the pressure-stat. It only took a few seconds!
This means that with the right modifications to the wiring, I could have a two position switch which would work in position one to provide the factory intended wiring path (for steam) and position two for PID control and most-importantly, compressed air from the pump with the pressure-stat acting as it's on-off control!
My next step from here is to package it in an elegant manner. Photos coming when as I make progress, maybe in a few weeks, as time permits.