I was considering to operate pneumatic actuators using Arduino, but usually electrovalves need 12Vdc or even 24Vdc (or some other 110Vac / 220Vdc) and I did not like the idea of being forced to use 2 relay for every electrovalve and the need of a 12/24 Vdc power source.
Then I had the idea of using a hand control valve and operate it mechanically using a "RC" servo. The pneumatic valve I had is a 3 position/5 ports (2 of which are the independent exhaust ports) control valve with a spring to return in the central position. The problem was that this return spring was quite stiff and the force required to move the valve was too high for a regular RC servo. Then I decided to modify the valve.
Step 1: Open the valve
I opened the valve unscrewing a couple of bolts and removing the black aluminium cap.
This revealed the end of the rod running through the valve and the return spring attached to the rod.
The spring is held by a couple of washers. Despite the diagram symbol of this kind of valve shows 2 springs on the opposite sides of the valve(meaning the spring returns the valve in central position no matter which of the other 2 positions were deflected before) the actual valve obtain the same effect with only one return spring. This is a good thing so you don't have to worry about finding 2 identical springs(for length and stiffness) and don't have to open the other side.
Step 2: Remove the stiff spring
The spring is held in place by a couple of washers and the first washer is held in place by a retain ring(snap ring e-type)
I removed the snap ring(E-ring) using a screwdriver.
then I removed the washer and the old spring.
At this point you could also reassemble the valve without any spring, this will allow the serve to operate the valve with the minimum effort but I preferred the idea of the return spring, just a much weaker one.
I looked around me to find a much weaker spring and I tried a piece cut from the tiny springs contained in retractable pens
Step 3: Replace the spring
I took the spring from a retractable pen.
It was too tight to fit on the rod and then I forced it on a larger diameter rod(like a screwdriver) to enlarge the spring diameter. I also pulled it a little(to obtain a longer helix step)
Then I cut a small piece of the spring.
I placed it on the valve rod between the washers
I put the e-type retain ring back in place and reassembled the black aluminium cap.
Now the valve requires less force and in the "next episodes" I hope to show you how to connect this to a servo and operate the valve with arduino and only 5Vdc source avaiable