After successful testing of my prototype pneumatic pinch valve with a 3/8″ bore, I proceeded to design another version with a full 1/2″ bore. This version uses silicone tubing instead of latex, which I believe will not contribute any off-flavours, and will not break down eventually as latex tubing is prone to do. In addition, it also has pipe-thread connections for inlet and outlet so it can be plumbed into a system easily, but can be removed if necessary. And no silicone tubing is exposed outside the pressurized jacket, so it won’t have problems with the tubing inflating and bursting as in the prototype version.
I used all household copper plumbing fittings in this design. Soldered together to form a pressure-tight seal. It’s quite inexpensive compared to commercially-available solenoid valves.
Here are the parts I used:
- 3/4″x1/2″x1/2″ copper reducing tee
- 3/4″x1/2″ copper reducer coupling
- Two 2″ lengths of 1/2″ copper pipe
- One 1″ length of 1/2″ copper pipe
- One 2″ length of 3/4″ copper pipe
- Two copper 1/2″ socket x 1/2″ FPT adapters
- Copper 1/2″ socket x 1/4″ FPT adapter
- 3″ length of 1/2″ID silicone tubing (obtained from a local industrial supplier, Rubberline.)
The reducing tee and the reducer must both be drilled through with a 5/8″ bit, to remove the stops that normally limit the depth of copper tubing being inserted. We need to run a length of 1/2″ copper pipe straight through, so the stops must be removed. Drilling with a 5/8″ bit does most of the work, then a little more work with a small round file and some elbow grease will allow the copper pipe to slide through without too much resistance.
Here’s how the pieces fit together:
First assemble the silicone tubing with the two lengths of 1/2″ pipe, overlapping by about 1/2″. It’s a bit of a stretch, but it’s doable. I would have liked to put some kind of hose-clamp on here, but there isn’t enough space for it inside the 3/4″ pipe. In testing, it appeared that the simple friction fit seemed to withstand household water pressure, around 48psi in my house.
If you’ve never soldered copper tubing before, you might want to look over my quick introduction. The most important things to know are: lead-free solder, use acid paste flux, and clean, clean, clean.
Clean (with wet-sandpaper or a steel brush) and apply solder paste to the end of the 1/2″ pipe, to the 1/2″ port on the tee, and the 1/2″FPT adapter. Insert the 1/2″ pipe into the 3/4″ side of the tee, and out the 1/2″ side. Slide the 1/2″FPT adapter on the end, and solder both the adapter and the tee.
Clean and paste one end of the 3/4″ pipe and the 3/4″ port on the tee, and solder those together.
Clean and paste the other end of the 3/4″ pipe, the other end of the 1/2″ pipe, both ports on the reducer, and the other 1/2″FPT adapter. Slide the reducer over the end of the 1/2″ pipe and slide it along to mate with the 3/4″ pipe. Slide the 1/2″ FPT adapter onto the end. Solder at both ends of the reducer, and the FPT adapter.
Finally, clean and paste both ends of the remaining piece of 1/2″ pipe, the 1/2″ branch of the tee, and the 1/4″FPT adapter. Assemble them together, and solder both joints.
Here’s a cutaway view of the finished product:
And a photograph of the real-world one:
I tested the valve controlling my household water pressure, which I have measured at around 48psi. If it can seal 48psi water, then it should have no problem with the 5psi or so that comes from a March 809-HS pump typically used in homebrewing.
In testing, though, I found I couldn’t really get a tight seal, even at 60psi control pressure. But it did slow it down to an almost undetectable trickle. I’m not sure why, since the 3/8″ prototype valve seemed to seal tight at a much lower pressure.
The reason it didn’t seal perfectly may be related to something I read in the Instrument Engineers’ Handbook (Google Books page): to seal tight, a pneumatic pinch valves needs a control pressure about 45psi above the line pressure. In my case, that would be around 93psi. I’m a little hesitant to pressurize the copper tubing that much without some more research to see if it’s safe.
In any case, though, I’m sure it will be fine for controlling wort flows from a March 809-HS pump. Perhaps I’ll fall back on an off-the-shelf solenoid valve to control the incoming water supply to my brewing system, and uses these pneumatic pinch valves everywhere else.
- Google Sketchup model