# Solenoid Valves

I'm using a peristaltic pump to pump viscous and sticky fluids through some tubes. I need to be able to "turn" the tubes on and off, and have been using solenoid valves - which works great.

However, I'm worried about this in the long term (and I have only purchased a small number of valves or testing purposes currently). Soda syrup is the medium, and I feel that it is going to easily gum up the valves and they will fail or need to be cleaned rather frequently. Before I go and purchase 20 more of these valves (only about $6 a piece, but that still adds up quickly) - I want to make sure that I address this potential problem. So I started researching types of solenoid valves, and I discovered there is a "solenoid pinch valve" which allows the liquid to never come into contact with the valve itself (the same reason I decided on using a peristaltic pump). However, everywhere I look, these things cost$50+ per valve. That's insanity! Why are they so expensive? Anyone have any ideas for how they could be cheaply DIY'ed? Custom manufactured by a local business? Or is there a cheaper type of electronic valve that could accomplish this? I'm kind of stuck at the moment...

Ideally I'd be looking for a 12v DC 2-way normally closed valve, at under \$15 per valve.

There are many valves, but just one pump. Only one valve opens at a time. So toggling the pump on and off is not a solution. The pump will be on, and one valve will be open, drawing only that liquid through the pump and out. After the correct amount (less the remainder of what is still in the tube) has been dispensed, one valve will open to the air to purge the system so it is (mostly) clean for the next run, to avoid cross contamination.

• Isn't it sufficient to simply stop the pump? – Dave Tweed May 29 '13 at 20:25
• @Dave - my first thought as well. Something that would squeeze the tubing should work. – JIm Dearden May 29 '13 at 20:38
• You guys kinda missed the point - one pump, many valves. I updated the question so it's a little more clear what I'm trying to do. – sarink May 30 '13 at 20:27

The tube passes through the end of the clamp which is shaped like a J to ensure it can't fall out when being squeezed. A round nosed piece of plastic with a screw thread through it can be moved between two guides that only allow forward and backward motion. As the FIXED (12V) motor turns the threaded screw attached to its shaft the pinch block moves forward or backwards depending on rotation direction. The adjustable limit switches are there to prevent the pinch block from moving to far in either direction.

• That seems like a pretty solid design. I'm assuming the "rounded pinch block" has like a V at the end of it? – sarink May 30 '13 at 20:46
• Yes, its rounded so it pinches the tube shut instead of cutting it in half. The peristaltic pump does something very similar if you can stop it when it pinches the tube. – JIm Dearden May 30 '13 at 20:46

I also wonder at the need for separate valves or pinch valves when the peristaltic type pump is already always pinching the tubing in at least one spot all of the time.

I know normally that a shopping question / answer is not standard practice on this site.....but..... the source for a reasonably priced pump may very well be of interest to many readers here.

You can get this sweet little 12V peristaltic pump from AdaFruit for less than half what was listed on the original question for a solenoid valve. Even less if you end up needing a whole bunch of them.

The pump runs through a geared reducer off the motor so it can produce a lot of torque. Running current is listed at 300mA from a 12V supply.

• I wonder if most peristaltic pumps don't pinch the tube completely, and instead rely on the fluid's viscosity to make the pumping action work. – Connor Wolf May 30 '13 at 4:26
• @ConnorWolf - The pumps I am familiar with do a complete pinch. As such they are even self priming. The fluid moves through the tube by being forced along by the pinch roller motion along the tube. On the AdaFruit one can even reverse the motor and it can then pump in the opposite direction. If one wanted to try to prevent a few drips from the exit tube when the pump is stopped it could be reversed for a short time before stopping the pump as a shut off valve. – Michael Karas May 30 '13 at 7:33
• The only peristaltic pumps I know anything about are the ones they use for blood, and those do not do a complete pinch, so they don't rupture blood cells. Other then that, Ok. – Connor Wolf May 30 '13 at 8:49
• It actually gets pretty complicated. As was explained to me when I asked a question about peristaltic pumps on robotics robotics.stackexchange.com/questions/1167/… – sarink May 30 '13 at 20:29
• Something like that would be perfect, except that its flow rate is 100ml/min...which is incredibly slow. This is the reason I wanted to purchase one big fast peristaltic pump, and use many pinch valves. – sarink May 30 '13 at 20:39