Monthly Archive for May, 2008

Solenoid valves for brewing

I’ve been brainstorming a design for a new home-brewing system. I’d like it to be capable of both recirculating (RIMS) and stepped-infusion mashes, and to have a large degree of automation. If I actually follow through on all my ideas (which would be the first time), it would probably be a system that Labbatt’s would envy.

What makes automation really awkward, however, is the need for computer-controlled (solenoid) valves. To work well in this application, there are a few requirements:

  • Fairly large orifice, at least 3/8″. If a piece of malt or grain husk gets in there, we don’t want the valve to clog.
  • Withstand mash temperatures, up to 175F.
  • Need to be able to operate with only a few PSI pressure. This rules out many “piloted” type solenoid valves.
  • Food-grade. Ideally NSF-certified. No brass, preferably stainless steel.

You can buy solenoid valves that meet these requirements, but they cost $$$. Typically over $100 each for diaphragm valves. Electrically-actuated ball-valves would be even better, because of the big and smooth orifice, but they’re into multiple hundreds of dollars each. Most RIMS brewers who try to go automated seem to just give up and use much less expensive brass-bodied diaphragm valves, use that “pickling” process to get rid of the surface lead, and pray.

I was brainstorming ways that I might build my own valves to these requirements. I came up with one idea: a pinch valve. A pinch valve is basically just a piece of flexible tubing, and you pinch it shut. Just like those plastic clamps homebrewers use on siphon tubes, but with a solenoid instead of fingers. Pinch valves have many nice properties for this:

  • Only one wetted material: the tubing itself. Pinch valves are popular in high-purity applications like pharmaceuticals for this reason.
  • Very large and smooth flow path when open, basically equal to the size of your tubing. Resists clogging even with chunks in the fluid.
  • Can close even around solid chunks in the fluid. This is why they use them in waste-treatment and other kinds of slurries or dirty liquids.
  • Mechanically very simple. Can be built at home.

Now, you would think that a pinch valve couldn’t handle much pressure, and you’d probably be right. But if I use the fairly standard March 809-HS type of pump, then I don’t have much to worry about. It’s an impeller-type pump, and March Pumps claims they can produce only about 12ft of head. Given that 1ft of water column is equal to 0.433 PSI, that means the March 809-HS pump is maxing out at about 5 PSI. If I can get a pinch valve to hold 6 PSI reliably, then that’s good enough. Truthfully, the valve probably won’t ever see the full pressure of the pump, since generally at least one path would be open. Otherwise, I would turn the pump off.

I decided to try to prototype one, to see if it would work. I looked in my junk drawers, and found an old 24VDC solenoid of indeterminate strength, and a DC power-supply that could drive it. And a short length of 3/8″OD latex “surgical” hose. I wouldn’t use latex hose in the final project, because of its short life and the rubbery taste it gives; I’d probably use something like the silicone hose that Austin Homebrew sells; I suspect it would be similarly flexible to the latex hose.

Prototype solenoid pinch valve

I banged up a klunky pinch-valve mechanism out of wood. Basically, the centre block is fixed. The solenoid pulls on the outer block, which then squeezes the tubing against the fixed block. The outer block has a V-shaped ridge to apply a more focused force on the hose.

I hooked it up to my CO2 regulator to test it for leaks. Sadly, it does leak, even at 5PSI. But I’ve got a couple more ideas to improve it. I can try putting that V-shaped ridge on both the moving and fixed blocks, thus getting a more focused force on both sides of the hose. And I could also try to figure out just how strong this solenoid is, and maybe try a stronger one.

Back to the drawing board…

[Follow ups: Pneumatic pinch valves and an Improved 1/2″ pinch valve.]