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How To Make A Rotating Fly Sparge Arm For All Grain Brewing

Ever since I started brewing all grain beer, I’ve wanted one of those cool rotating fly sparge arms. They revolve around and distribute water on your grain bed so all the precious sugars are washed from the grains. There are two schools of thought; the first being don’t use it and just keep an inch of water on top of your grain bed and the other is better efficiency when fly sparging over a longer period of time. Whichever you prescribe to; this is a cool little project! Read on and I’ll show you how to make a DIY rotating sparge arm.

All of the materials can be found at a general hardware store, hobby store or craft store. Everything should cost under $10 dollars. I even found an online hobby stores that sell everything for less than $6 dollars plus $4 dollars shipping and handling. I recommend going to the store and trying the pieces together.

The basic premise is you want the 7/32” tube to fit snug, but turn freely in the 3/16” tube. The 3/16” tube will fit into the 1/4″ tube with the 4 O-Rings and should be held together tight. The design works flawlessly, but you need time and patience.

Schematic of Fly Sparge Arm.

Build Of Materials

1 X K&S Engineering Round Brass Tube 7/32” x .014    (Stock #130)

1 X K&S Engineering Round Brass Tube 3/16” x .014    (Stock #137)

1 X K&S Engineering Round Brass Tube 1/4” x .014    (Stock #131)

4 X Rubber O-Rings that fit around 7/32” tube and fit tight into the 1/4” tube

2 X Rubber O-Rings that fit around 1/4″ tube

2 X 3/16” plastic bolt covers

A plumber’s torch

A tubing cutter

An auto center punch

Some vice grips or something to hold the tube together that can stand heat

Some chapstick or Vaseline

Sand paper

Take the 7/32” tube and cut it into a 3” piece and a 9” piece. Be exact on the 9” piece, because this will become the fly arm and you will want to keep it balanced.

9 Inch Fly Sparge Arm and 3 Inch Stem

Lay the 9” piece against the tape measure and score it lightly 4 1/2″ in, then take the center punch and set the spot for drilling.

Drill a hole 1/2 the size of the tube diameter in the middle of the 9” piece of 7/32” stock as a pilot hole. Then select a drill bit a little smaller than 7/32” of an inch. I used a caliper, but you can just match it up. The key here is you can always take more metal off, you can never put metal back. You will want the 3” piece of 7/32” stock to fit snug in the hole. If you own a Dremel start using it now and finesse the hole larger while checking it every step of the way.

Choosing the drill bit for the pilot hole.

Sand both the 3” 7/32” stock and the 9” 7/32” stock and prep it with plumber’s flux.

Sand and prep the two pieces for soldering.

Now for the hard part: make sure the

3” stock is at a perfect right angle and it just pushes in far enough to cover the sides, but not all the way as it will restrict flow of water. Heat the tubes with the torch and make sure it does not move in the jig. Then gently apply the solder, just using the resonant heat from the pipes. Not too much solder! Just enough solder to fit and keep it together, but not enough that it puddles inside the tube. Remember it needs to allow for flow and be balanced in the end.

Soldering it together in the jig.

Now drill holes on the right side 1” from center and every 3/4″ then double up on the end at 1/2″ and 1/4″. The ends should have a lot of flow compared to the middle; this will help propel it around. Use a 1/32” or 1/16” drill bit to make the holes. Then flip it and do the same on the other side. Make sure you have hole on opposite sides as this will be how it propels itself around; just like a garden sprinkler.

Drilling the holes on Side A.Drilling the holes on Side B.

Cut the end caps if they are really long and put them on the ends, however later this is how you can balance the arm so don’t cut too much!

Putting the End Caps On.

Next take the 3/16” stock and cut it at 2 1/2″ inches. If you are using a tubing cutter, it will knurl the end and make it smaller. Use a drill bit and sand paper to make it true again and make sure it floats on the 7/32” stock.

Measure and Cut of the Bushing.

Fit the 3/16” stock over the 3” stub of 7/32” fly arm and gently expand the 7/32” tube so the 3/16” tube doesn’t come off. I used a small drill bit and put it inside and slowly started running it around the inside to smash it out. Later I found out I had some high spots, so I used rubbing compound to smooth it out. This part took a lot of jerking around to make sure it spun smooth.

Fitting the Bushing on the sparge arm.

Once it spins freely with the weight of the arm hanging on it, put the four O-Rings on. Lube the outside of the O-Rings up with chapstick or Vaseline, just the outside of the O-Rings. Then get ready to insert it into the 1/4” tube.

Putting the O-Rings on the bushing.

Push it in snuging the O-Rings into the tube and press it together until the 3/16” tube is flush with the 1/4″ tube.

Pressing the assembly together.

Drill a 1/4″ hole centered into the piece of 18” wood. Then place the O-Rings on the completed sparge arm to adjust height.

The Finished Product.

You can further trim the 1/4″ tube down; I cut mine down to 5”.

You may need to neck the 1/4″ tube up to 3/8” or 1/2″, just use 1” pieces of hose to do so.

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Final Product

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