Saturday, November 28, 2009

Gaggia Preheater Construction Rev 1

I am adding a preheater to my Gaggia Classic, here is my first attempt to do it.

There are some people who have done this by wrapping copper tubing around the boiler of Gaggia's. 
I was going to do it this way, I even bought the copper tubing, but when I tried to install the tubing, I found it was hard to wrap it around the boiler, so I wondered if there was another, easier way to do it.  I was also worried the copper tubing would not have enough volume.

Example 2 of copper tube preheater

here a guy machined a preheater for his gaggia.  Would be the way to go, if I had a milling machine, but since I don't, I needed another approach.

I started thinking about another way to do this, then I found that a couple companies, Bud and Hammond make little, watertight boxes.  There is a flat part on the front of the boiler which I could strap this little box to.

I looked at what was available, and decided this box would fit the best
I calculated that it will hold 2 3/4 oz of water, and there will be about 5.5 square inches of surface area where the body of this box will mate with the front of the boiler.

Here is a pic of the body of this box.
I had to do a couple things to this box to make it work.  The first was to mount a couple tube fittings in the box.  I bought these fittings from Mcmaster

They have a 1/8" BSPT thread on one size, and a 6MM push to connect hose fitting on the other side.
1/8 BSPT thead taps are expensive, but you can use a 1/8-27 NPT pipe tap instead.  It is close enough, and it worked fine.
I drilled and tapped holes on both sides of the box.

The other change I made to the box was to add some internal dividers, so when cold water comes into the box, it will take a little while before it cools down the outgoing water.  I bought a sheet of thin aluminum from my local hardware store, and cut it to size, then drilled a couple holes in the ends.   When installed, the holes were put on opposite sides of the box.



These were glued inside the box, to divide it into three sections. hopefully to keep the outgoing water hot longer, as cold water comes into the box.

I used food safe high temp RTV to glue the dividers in place.  I also used RTV to seal the tube fittings, I put RTV in the holes before I screwed the fittings into place.

I also installed a thermocouple near the exit fitting, so I could measure the water temp close to where it exits the preheater.





The last thing I did was put RTV around the edge, on top, before I screwed the cover on.

To install it, you need a one more tube fitting from Mcmaster
6mm push to connect coupling

You also need some 6mm, Teflon tubing
6mm Teflon tubing

Installation is pretty simple.
You cut the tube the connects the pump to the boiler, near the pump.
You connect the tube from the boiler to the output of the preheater.  In my case, the output has the thermocouple, otherwise there is no difference between output and input of the preheater.
 
Then, you put the 6mm coupling on the tubing from the pump, and add enough 6mm tubing on the other side of the coupling to reach the input of the preheater.
 
The preheater is mounted on the front of the boiler, with a hose clamp to hold it in place.  I sanded the flat section of the boiler, to make it flater.  Before installing, I put thermal grease on the preheater, to get better heat transfer.
 
You now have a preheater.

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