Do Pistons rotate?

[guruboy]

Had this thought recently.

Take a fully assembled and working piston regulator.

Does the piston rotate as its being used?

Rotation is not part of the design, but nothing keeps it from happening.

 

[redacted]

While it probably would not matter, for the piston to rotate, there would have to be a rotational force which seems to be absent. That force would have to overcome the force of friction between the piston and the spring or the spring and the body.

 

[Ghetto Diver]

I had thought about this a while back after seeing a plastic shim chewed up a bit. I believe there is a minimal amount of movement, but I think that is/was due to an uneven spring surface.
I would also think that the HP seat would be cut deeper and wear sooner.

Kinda like trying to see if the fridge light stays on when door is closed.

 

[divad]

Kinda like trying to see if the fridge light stays on when door is closed.

I hate that...

 

[KeithG]

The piston will rotate a negligible amount. The direction may be random?

 

[NotSure]

The piston may rotate slightly because there is a torsional force created when the coils of the spring are compressed. As DESRAT mentioned the result can be seen sometimes when the spring twists into the shim. I would think that the piston would return to it's original position when the additional compression force is removed but it may not depending on counteracting force from the shim / regulator body. This may be why some regulator companies recommend lube on the spring ends an other don't.

 

[halocline]

I don't think the scubapro pistons rotate, but maybe a very tiny bit.

 

[axxel57]

Yes, I also don't believe that pistons rotate, but I'm pretty sure that the springs rotate forward and backwards while being compressed.
That would explain the often seen loss of chrome and scratch marks on the areas where the springs work when there are no shims used.......

 

[Alastor]

I think that the very end of the spring could slightly dig when compressed and would slip when released acting as a racheting device.

 

[halocline]

Don't forget that the springs are somewhat compressed even when the regulator is not pressurized, at least on SP balanced piston regs. So it's never 'loose' between the piston and the spring.