Water Treatment pH Cell and Bubble Trap

This is an alternative to the $650 flow cell Hach makes: https://www.hach.com/p-flow-cell-assembly-for-1-npt-sensor/9180100?srsltid=AfmBOorAh_jnr9vchCoAR8iePuVS0UdWyWtmIoFehLCUOxG76RrTjTVv

There are two versions, one for 1" NPT probes and one that is a bubble separator for NTU meters.  The drawings show them combined for conceptual purposes but the top assemblies are different.  The pH cell is designed to allow a standard lab probe to go into its own little hole for doing direct comparisons to the process probe (if you have a battery powered one like a Hanna or VWR)

The inlet stinger flow break can be used to add more flow to an existing HACH cell without shooting water out of the top.  For this, replace the valve at the bottom with a John Guest 3/8" NPT to 3/8" PTC valve, and stick 1/4" straight PEX into the hole at the threaded end (see the pictures)

Materials:

• 3" OD clear Acrylic Tube (6ft, ~$90 shipped, makes 6 bubble traps or 9 probe cells):  https://www.usplastic.com/catalog/item.aspx?itemid=32523&v1=&v7=&gad_source=4&gad_campaignid=17338915591&gbraid=0AAAAAD_wVCY2TTysK0hn4AAIBEE5VorBF&gclid=Cj0KCQjw267GBhCSARIsAOjVJ4Gj673YRKBuhhAW-7zuLLoERyHxmfDUpYop7QhfRB_j4A0fvSxreDAaAtKpEALw_wcB

• 3/8" NPT to 3/8" push-to-connect fittings (2 per flow cell, you will also need 2, 3/8" ptc valves and a reducer to 1/4" for NTU meter lines) https://a.co/d/00Zruh7U

• 1/2" NPT to 1/2" push-to-connect fitting (one per cell for the overflow) https://www.supplyhouse.com/John-Guest-PI011624S-1-2-OD-x-1-2-NPTF-Male-Adapter?utm_source=google_ad&utm_medium=Shopping_Plumbing&utm_campaign=Shopping_X_Plumbing_X_SSC_New&utm_campaignid=22376725605&utm_adgroupid=175817623134&utm_targetid=pla-2435663902799&utm_product_id=PI011624S&utm_matchtype=&utm_keyword=&utm_adtype=pla&utm_category=Plumbing&gad_source=4&gad_campaignid=22376725605&gbraid=0AAAAAD_WAysXSQ8nVG03obzGC1y1vTs4L&gclid=CjwKCAjwmdLSBhANEiwAkREMNwMemFKFST6QZcaCMk4ktOkvoOJnCHdASR0MoUP8TzoZagYSJGgjARoCGTAQAvD_BwE

• 1/4" straight PEX (for the bubble trap stinger) https://www.homedepot.com/p/Apollo-1-4-in-x-5-ft-White-PEX-B-Pipe-APPW514/301541226

• Thread tape

• NSF grease for the female threads (pro tip to waterproof threads better)

• 2x M4 nuts for the mount clamps

• 2x m4x15 (at least 15mm) screws for the mount clamps

• 4x M4x10 (up to 15mm) screws to assemble the mount clamp

• Aquarium silicone glue (I used Selsil 07 but most should work

• A paint stick with one corner rounded for smoothing out the silicone glue bead at the bottom of 8-12" of clear tube (see the pictures)

Printing:

4-5 perimeters minimum for everything if you want it tough and waterproof.  I recommend 0.15mm layer height to get the threads and overhangs cleaner.  for the top sections, the rim where the clear tube seats will need supports.  I set them to build plate only and the overhang threshold to 2 degrees.  be sure to sand out the seam where the clear tube goes on the top and bottom sections.

Assembly:

• For the bubble traps I did 12" of clear tubing and 8" for the pH probes.  Cut the 1/4" PEX the same length as the clear tube (bubble trap only).  Cut them SLOWLY on a chop/miter saw.  The ends came rough and not square at all, FYI.  

• Dry assemble and mark the depth the tube goes into the tops and bottoms.  One end at a time (bottom first) apply a thin layer to BOTH the mating surfaces of the tops/bottoms AND outside of the clear pipe (like you would if you were cementing PVC pipe together).  Press the tube in slowly TO THE BOTTOM FIRST without twisting.  carefully wipe off excess silicone glue into a neat bead around the bottom.  Use the paint stick rounded corner to carefully do the same to the inside bead, being careful not to smear any excess on the inside when taking globs out to wipe on some towel.  Repeat for the top sections, but you can use your finger on the inside of this end. 

• Most aquarium silicone needs 48 hours to fully cure.  You'll need about 8 hours before adding the fittings and caps to be safe.  Place the curing cells by a little desk fan or something.

• Use a small terminal screwdriver to help stab the cap and lid tethers into their holes on the lids and the tops.  They can be pushed in about halfway, but the other sides will need a bit of pushing or prying from inside to get them through.  Watch your fingers and do it against a table.  Placing the tethers in hot water helps make them more pliable.  The lid seals go in with the angled edge facing out.  Use your fingernail or a small screwdriver to help fully seat the edges into the base of the caps.

• The mounting clamp can be assembled for horizontal or vertical channel strut, depending on how you orient it while assembling.  Grease the holes on the clamp for the screws (3d part pro tip).  The collar is needed to secure the flow cell to the clamp (look at the little tabs that lock it in place) and the whole thing is designed so you can take the tubing off, remove it, and clean the cell easier.

• Add a bit of grease residue to the threaded parts.  They should go together with ease but this really makes them fly.  

• Thread tape the PTC fittings and grease the female threads a bit.  The fittings should go all the way in with only 3-6 wraps of thread taps each.

Hopefully this and the pictures should cover everything.  If this saves some municipality some money I'll be happy.  You can build about 30 of these for the price of one the Hach flow cells.