choosing the right solenoid valve

Hello, I am looking for a pneumatic solenoid valve that can be used to control the motion of a piston in a double-acting cylinder. The descent of the piston drives the esxtrusion of a viscous material contained in the lower section of the cylinder through a small orifice. After doing some research I had come to the conlcusion that the type that's best suited for the purpose should be a 5/3 valve with operating pressure between 0 and ≥4 bar, but when I went looking for one I could only find valves with a minimum pressure of 1.5 bar, which I can't use since the pressure needed to achieve extrusion at the desired rate is generally ≤1 bar. I turned to looking for 3/2 direct-acting valves thinking I could use two and obtain the same result as with a 5/3, but even if it worked it would still be preferable to have one component instead of two.

What I came here to ask is:
1) do all 5/3 solenoid valves have a minimum differential pressure? If so, why? Are they all pilot-operated? Our system is currently equipped with a 5/2 manually actuated valve (it's described as 5/2 on the datasheet, but I think it works more like a 5/3 open center valve because if its lever is moved to an intermediate position the piston stops where it is*) which has a max pressure but no minimum pressure
2) would the 2x3/2 valves workaround actually work?
3) * if our manually actuated valve has three positions, why does the datasheet say 5/2? (diagram below)

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Thank you :)
p.s. I am very new to the field, please forgive me for any conceptual or terminological mistakes

Welcome to the field. Please take this advice from a white-haired old engineer. The best of source of technical information and guidance is available directly from the manufacturers and their distributors. All the major manufacturers have application engineers and local distributors. Their only job is to help you successfully choose and apply their products. It has amazed me over the last several years how few young engineers take advantage of these services. I guess if you grew up with Google as your only source of general or technical information you might not think of these other sources.

So call a couple of the major manufacturers and ask for an application engineer. Talk directly to a live person.

Also, confirm that the current valve is indeed the model you think it is. If the manufacturer's information says it is a 5/2, its a 5/2. Just because you can stop a handle in the middle of it's travel does not mean it is designed for that.

Your description is unclear. Are you saying that the piston has air on one side and extrusion material on the other? Or is the extrusion device separate from and driven by the cylinder? A pneumatic diagram would help.

If you intend to operate this cylinder at this low pressure, you should be prepared for some trouble. All cylinders have internal friction, and this friction is a major issue when operating at low pressures. The resulting action will be jerky and uncontrollable. Redesign your system so that higher pressures are required.

The only reason I can see for a valve to have a minimum internal differential pressure is if there is an internal pilot valve. If you redesign for higher pressures, that won't be an issue.

First of all, thank you for your reply!

Your guess is correct. At one point I did think about contacting a manufacturer, but I wasn't aware that they had people whose job is to guide customers in finding the right product (though it does make a lot of sense), and also I was trying to learn enough on the subject to be able to communicate effectively what I'm looking for before bothering someone about it, so I waited, but we're definitely going to do that soon.

I know the diagram matches the valve because it's also printed on the valve itself, yet it's being used as if it had 3 positions... if it is being operated improperly, it's possible that it's being damaged. Good to know.

My description was actually wrong, sorry, the extrusion device is separate from and driven by the cylinder:
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[QUOTE=jboggs;17803]If you intend to operate this cylinder at this low pressure, you should be prepared for some trouble. All cylinders have internal friction, and this friction is a major issue when operating at low pressures. The resulting action will be jerky and uncontrollable. Redesign your system so that higher pressures are required.[/QUOTE]

This is something that I will definitely bring up the next time I see the people who are in charge of this project.