Change In Legality of Certain Solenoids?



Has there been a change to the rules governing the specifications of what solenoids are legal this year? R84 C seems to suggest that solenoids with 1/4 in NPT, BSPP, or BSPT ports are illegal. Our team has been using this kind of solenoid for years. Is this new this year? If so, which solenoids should I be using?


I think you meant R84 C:

Solenoid valves with a maximum ⅛ in. (nominal, ~3 mm) NPT, BSPP, or BSPT port diameter or integrated quick connect ¼ in. (nominal, ~6mm) outside diameter tubing connection

This is actually more flexible than the 2018 and 2017 rules, which didn’t allow integrated quick connect:

Solenoid valves with a maximum ⅛ in. (nominal) NPT, BSPP, or BSPT port diameter

Are you sure your solenoids are actually 1/4 in NPT?

SMC solenoids like those sold by VexPro are probably the most common ones used by teams.


Yes. Based on some of the images of the example fittings on the vex products which are 1/4 press terminals, I can confidently say that the ports on our solenoids have a diameter of 1/4 in.


Just to make sure, a 1/8 in NPT fitting has an outer diameter on the threads of around .4 inches and looks like about a 1/4" hole. A 1/4 in NPT fitting has an outer diameter of the threads of over .5 inches.


Sounds to me like you’ve been getting away with illegal solenoid valves a while. 1/8" NPT was the largest allowed by the rules until this year explicitly added 1/4" push tubing terminals.


So the spec of the port is a radius and not a diameter? The diameter of our fittings fits in to the solenoids, whose ports are about 1/4 in in diameter.


It’s a pipe size. A 1/8" NPT fitting (female side) will look visually like about a 1/4" hole. Based on your description I think you’re okay. A part number of the solenoid would let us check for certain.

Another link:


Well, that’s certainly confusing at least. Thanks for the clarification. I currently have no way to get a part number for it, as I’m at home, but I’ll be sure to check it out if I do.


NPT (National Pipe Thread) fitting sizes can sure be confusing! The size is based on a nominal inside diameter of a thick walled pipe, so the threads are much larger than the nominal size.


Pipe and conduit sizes are based on (approximate) inside diameter and tubing size is based on (approximate) outside diameter. Both 1/8" NPT fittings and 1/4" plastic tubing mean that the airway is not much larger than 1/8" diameter.