Single Acting vs Double Acting Strength


We’re considering buying the pneumatic kits this year. I did some searching but couldn’t find any specifics on the difference in strength between the single and double acting cylinders.

How much weaker are the singles on a return stroke than the doubles?

Don’t have numbers, but also be aware that a single acting piston is also weaker on the extend stroke, since the air has to fight the internal spring, whereas on a double acting piston the pressure must only overcome internal frictional resistance.

Here’s the SMC Datasheet

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As JoeG said, the extend stroke of Kit 1 Cylinders (single acting) is slightly weaker than the extend stroke of Kit 2 Cylinders (double acting) because the return spring in Kit 1 Cylinders oppose the piston extending.

The return stroke of Kit 1 Cylinders is very weak, as it’s just the spring inside the cylinder pushing the piston back. The return stroke of Kit 2 Cylinders is slightly weaker than the extend stroke of Kit 2 Cylinders (due to the piston rod effectively removing surface area of the piston), but is much stronger than the return stroke of the Kit 1 Cylinders, as it is actually powered by air.

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I have no numbers for this, but in my experience it seems like the single actings are about half the strength of the single actings on similar pressures. The other advantage of dual acting cylinders is that the strength can be controlled in both directions via the regulator. The stroke is shorter on the dual acting cylinders than the single acting cylinders.

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On the product pages, it says the stroke for both is 55mm. Is this incorrect?

I mispoke. The physical single acting cylinder is longer. The distance the internal part come out may be the same. Im not positive. If the vex page says it is the same than it most likely is. But i am sure that the physical single actings cylinder is longer than the double-acting cylinders.

The difference between the length on the Single acting a Double acting is so large that at worlds Vex thought a single acting piston was not vex issue because of lack of use by teams.

Another difference is that the body of the double actings are shorter and can be used in smaller spaces. The speed can also be controlled with the flow valve. Also if you need to save air and don’t need pressure in one direction you can always plug one end of the solenoid and rubber band the piston to get the same effect as a single acting…

The single actings are longer because the spring inside ( correct me of I am wrong?)

Overall the double actings are a better investment in my opinion but after your first 2 kits I would say just purchase the parts you need and even then the price vex has the solenoid cables at makes it so you can’t save much money on buying elsewhere unless you need replacement parts.

Keep note, the CAD VEX has for the single acting piston is not accurate dimensional wise. This is not VEXs fault I tried downloading the part directly from SMC and had the same issue.

  • Andrew

As Andrew has said, the CAD is not correct. It seems to be shorter than it actually is.

However, the CAD for the double acting cylinder seems to be mostly correct, although last I checked it was off dimension by a little bit.

Sorry to revive this old thread but how do you plug one end of the solenoid? Is there a part in the double acting kits we can use?

I think he meant “Plug one end of the cylinder/piston”, not solenoid. (?)

By the way, does anyone know if it actually needs to be plugged? Maybe this would still work if no hose was connected to one end (with the rubber band). :confused:

Have a look at this. I think it’s what you are wanting…

The flow control valve on the piston that is not in use does not need to be on the piston.


Thanks - that’s exactly what I needed!!

I was wondering if the dual action pistons may start in an extended state such that the solenoid triggers a retraction by reversing the air lines on the piston.

That works.


The solenoid has 2 outputs. Output B (not sure if it is A or B, I think it’s B. Try B, if it is backwards then swap to A) is the default, so before the game there will be air flowing through this one. So, you would hook this output up to the connector on the piston which gets it to extend (the one at the base), and the other output to the connector on the piston that gets it to retract. Basically, you can choose whether or not the piston is extended or retracted before the game, it just depends on which way around you have the piston connected to the solenoid.