3A sanitary pumps are out of reach to homebrewers. Their price is at least an order of magnitude higher than what most of us are able and willing to spend. Recently, some brew-it-yourself-ers who are interested in sanitary design, but not so much the associated costs, have been modifying affordable food grade stainless steel pumps to be mostly sanitary. I am now amongst their ranks.
This is an approachable project for those with any soldering experience thanks to BrewHardware. BrewHardware has done the homebrewing community a solid by having parts machined which make the job as easy as it possibly could be. The parts I speak of are NPT-tapped tri clover end caps. These end caps will thread directly onto a pump head and can then be silver soldered into place (conveniently BrewHardware also has soldering kits for stainless steel – I have no affiliations with them, I swear!). Solder and flux selection for soldering stainless steel is very important. I’d suggest just buying the kit mentioned above.
There isn’t much to this project, but since I couldn’t find any progress pictures, or many details from those who have taken on sanitary-izng their brew pumps, I figured I’d put my process out there.
The very first thing you must do is to remove your pump head from the motor. You must then open the pump head to remove the impeller and all bushings and gaskets. Don’t lose anything.
Now you need to prepare the surfaces that will be soldered together. Use a stainless brush on the threads of both the pump head and the end caps to help remove dirt and oxides. Follow with a thorough cleaning using isopropyl alcohol.
You will then want to actually place the tri clamp end caps onto the pump head by threading them clockwise. You could try to thread them to the correct depth by eye… but there is an alternative as long as you have a flat rigid surface that can be used (perhaps an intact tri clamp end cap?). What you do is thread the end cap a couple extra turns clockwise, place the hard flat surface onto the face of the inlet or outlet of the pump that is now sticking past the end cap, and then lightly rotate the end cap counter-clockwise until it meets resistance. At this point the end cap and the pump should be totally flush.
Before continuing with the soldering, please ensure that you are working in a well ventilated area and/or you are using a chemical respirator. You do not want to be breathing in vaporized flux! Also, wear safety glasses or lab googles or something. Even worse than breathing in some flux fumes would be getting a splatter of super hot and super acidic flux in your eyes. What good is shiny brewing equipment if you haven’t eyes to admire it?
Secure your pump assembly such that the face of end cap that is to be soldered is facing straight up. Add liquid flux to the joint area, and start to heat your work piece with a propane or MAP gas torch. This heating should be very gradual, and away from the area that you will be soldering at first. Gradually move towards the joint area. The flux will start to boil as it heats up, apply more flux as it vaporizes, being mindful of any splattering that may occur. Do your best to keep the joint wet while not wasting any flux/not making a mess. Some flux will inevitably burn.
As an aside, if you were just using isopropyl alcohol to clean your work piece, as you probably were, move that somewhere else… and anything else highly flammable while you are at it.
We want to indirectly heat the joint to the temperature needed to melt the solder, and not much hotter. When you sense the joint is reaching this point, move the torch away, and test to see if your solder melts. If it does not, continue heating the joint another 15-20 seconds, and try again. When the solder is flowing you do not need to apply additional heat. If the solder begins to stick as you apply it, you need slightly more heat – a couple seconds with the torch only.
As to what the joint should look like… my suggestion is to let the solder visibly build up around the joint, and then sand it down flat. This is much much more solder than what is needed to join the pieces together, but will leave you with a perfect flat face.
Once you have reached the desired amount of solder on the joint do not do anything with it for a couple minutes. The assembly is very hot, and the solder will remain liquid for a minute while it cools down, and it’s best if it is not disturbed while it does this. Don’t burn yourself either.
When the solder has clearly hardened you can start to wipe up some of the burnt flux furthest away from the joint with a damp rag. Slowly work towards the joint. No rush.
My first soldering attemp is below:
After the burnt flux has been cleaned a bit…
And after sanding down with 220 grit…
I didn’t actually build up enough solder here to leave the fill area perfectly flat after sanding… it’s not bad, but there are visibly imperfections and there is room for improvement. These are easy to redo if you are not happy with your first attempt (or second, or third…). I hope these pictures show that something that looks ugly, covered in burnt flux, actually can turn out quite nice after some clean up. It is a bit nerve wrecking to take a torch to a couple brand new pumps, but it is not as risky as it may appear.
I worked on my technique a bit, and eventually I was able to get all of the fill areas just about perfect after sanding. Here’s what my finished pump heads look like:
I’m happy with these. As a bonus, there is something intrinsically satisfying about the perfect ring of silver solder between the stainless parts.