Combined pressure limiter valve and qualitative manometer idea, non-Le

[Sumendar]

Possibly an old idea, but I just successfully tested a pressure limiting valve made of a 2ml disposable plastic syringe and a rubber band. I made a small hole in the syringe body near the top of the scale, then wrapped a rubber band to hold the piston in. Now, when the pressure inside the syringe rises, the piston comes outwards until it passes the hole, at which point extra air starts leaking out. When the pressure drops, the force from the rubber bands overcomes it, and the piston moves back inside past the hole. Adjusting the rubber bands adjusts the pressure limit. As an added bonus the position of the piston gives an idea of how much pressure you have in the system compared to the limit, this could get helpful when deciding whether you need a higher-volume compressor.

Comparison to pole-reverser solution:

+Small by volume(my proof of concept piece is 13x3x2.5 studs long fully extended,)

+Cheap (the usual system requires a pole reverser and a pneumatic cylinder, not exactly the cheapest parts around)

+Doesn't require Lego connection

+Motor runs continuously -> Less fluctuation in pressure due to acceleration and deceleration of motor

-Large largest dimension (13 studs long might be too much for some uses, this can be reduced by stronger rubber band and lower hole location though)

-Can't attach to Lego connection

-Not Lego

-Butt-ugly

-Motor runs continuously -> heat can become an issue, part wear, battery lifetime

[Zerobricks]

Whata bout simply attaching cylinder to a normal lego 3 way valve, and when the pressure is high enough, the valve opens and air escapes...

[Sumendar]

The valve is closed when centered, so keeping it closed at low pressure might be a problem, as well as closing the valve once enough air has leaked.