I am working on a project where I have an air supply and a tank, I want to be able to control whether air allowed to fill the tank, the supply and tank are isolated, and the air in the tank is allowed to bleed to the atmosphere. I would be able to do this with a double action solenoid that has a neutral. What I want to know is if any of the solenoids that have been given to us in the past have this feature or if there is another way to achieve this with the solenoids that we are given. I know that I can do this by connecting an additional solenoid to the exhaust of the first solenoid, but it is a poorly functioning and overcomplicated solution.
I believe you are talking about a 3-position, center-closed valve. We have never received one of these as far as I know, only 2-position valves. You could probably find a used 3-pos. valve in the Ebayish market if you are in a position to buy one.
As you said the only way to achieve the same function with the 2-position valves we use is with multiple valves, but this should be pretty straightforward with 2 valves. With single solenoid, spring return valves (like the Festos), you could have one on the supply line, and one on the exhaust line, and simply fire one or the other when you want to fill or bleed. You’ll need to plug 2 ports on the valves to make them into simple open/close (“2-way”) valves. This setup would be essentially identical to firing either side of a 3-pos. valve, and work just as well.
I was hoping to avoid single action solenoids because I have had so many problems with them, I also don’t have enough outputs on my controller to use a double action solenoid for both fill and bleed. Are there different bases for the SMC solenoids that allow the solenoid to have a center off? If not, what is an inexpensive option for a double action center off solenoid?
The 3-position functionality is in the valve spool body itself, not in the base, so there is not a simple base swap that would provide that function. You would need a genuine 3-position valve. Here is one
http://cgi.ebay.com/4-Way-3-Position-Center-Closed-Solenoid-1-8-NPT-12V-DC-/260496278497?pt=Pneumatic_Hydraulic_Valves_Parts&hash=item3ca6c9c3e1
and there are others listed of larger sizes. They do not tend to be cheap, even on Ebay. I would say the only 'inexpensive" option would be if you were lucky enough to find a used one from a distributor or an outfit that breaks down and sells parts from industrial equipment.
My advice would be to not hold a grudge against single-solenoid valves. They are probably the most common type of solenoid valve ever used in every kind of commercial and industrial application. The Festo and other single-sol valves that have been included in past FRC KOPs are proven industrial valves made for long service. If you have had a bad experience with them then there was something wrong with it and you had bad luck. What problems have you had? We have used them multiple times with no trouble. They provide the functionality you are looking for with the limitations you have, and if you are with a team that has a collection of past KOP parts you probably have them already. Unless your project is life-or-death critical or will see extremely harsh or long service, they should work fine. If you have them, it costs nothing to try them first.
OK, I’ve got it working using two SMC single action solenoids. We have had the most problems with the blue single action solenoids, I don’t remember what company they are made by, although the Festos haven’t been much better. The main problem we’ve had is the solenoid simply doesn’t react when it is powered.
What is the voltage rating on those non-working valves, and what are you powering them with? A couple years ago, there were some KOP valves rigged for 24V…and there was a kit to get them to 12V.
They where 12v valves running directly off a robot battery, and it’s not that they never worked, they just worked sporadically.
Sounds like the valve spools may be sticking. You might want to lubricate them by sending a few drops of light oil through them (just drop it in the input line.) If they are used and have been sitting around for awhile, the o-rings in the spool can get dried out or contaminated and stick. These valves were meant to be used with lubricated air in industrial service, yet in robotics we ask them to work without ever seeing any oil. The spring return depends on the valve being lubricated to work properly. I have yet to ever find a team that has lubricated their valves (the cylinders need it too) by sending some oil through the lines, so I preach that whenever I can. I suspect it is the cause of many teams’ problems with valves.