Thursday, February 24, 2011

Modified Pressure Pot

Its one thing to explain this.  Its another to show you.  1picture = 1000 words.

Metal wear on the lid from lid clamps
The clamps that hold down the lid are made of cheap pot metal.  But they are metal.  And when you tighten the clamps, the metal against metal marks up and damages the lid.  Eventually, you will wear through the lid.  This pressure pot is normally close to $200.  I would hate to have to buy one every couple of years.

New threaded Pin for clamps
This is what I was describing earlier.  The clamps I have on my lid are a 10 mm x 1.5mm thread pitch.  So I took some aluminum bronze and machined it to 10 mm in diameter and then I machined a 1.5 thread pitch on the length of bar I just machined.  This bar will replace the threads on the lid clamps.

The threaded bar that will replace the clamp threads
Here is the length of threaded Aluminum bronze I made that will replace the threads on the lid clamps.
Clamp threads replaced with spring pin installed

First I cut the threads off  of the butterflies. Next I drill a 8.5 mm (tap drill size equals diameter minus the pitch.  It's easier in metric because in Imperial you have to convert the fraction to decimal form and then you are working with 3-4 decimal places instead of whole numbers.).  Then I put some lock tite on the threads and thread it into the butterfly.  Then I drill a 1/8" hole in the butterfly in a position that is right in the middle of both the threaded aluminum bronze bar and the butterfly.  Next I install a 1/8 spring pin.

Finished Clamp with new threads
The aluminum bronze is soft.  Its a cheaper viable option to brass.  The reason I did this is that now, the threaded aluminum bronze will mushroom.  We want this to happen.  Because it is softer it will mushroom and wear instead of the pressure pot lid.  When the threaded aluminum bronze  becomes too mushroomed and no longer works, I will punch out the spring pin and replace the threaded aluminum bronze pins and drill a hole in the same place through the new aluminum bronze threaded pin and reinstall the spring pin.

Close up of finished clamp
Now I realize not everyone has a lathe to machine the 10 mm x 1.5 pitch or whatever thread pitch your lid clamps may be.  You might be able to get some brass  bolts or cap screws.  You can use these just as well.  You just need to cut off the head of the cap screw or bolt. It took me 1 hour to drill and tap the holes, install the new threaded pins and drill and install the spring pins.  All in all a couple of hours and our pressure pot should now live longer than we will.  :~)

And if worst comes to worst, you cant find the parts or you don't feel comfortable doing this...drop me a line at   I'll do it for you for a VERY reasonable price. 

Now the only thing on our pot that will need replacing is the seal every so often.

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