SMC Solenoid Manifold Deem NOT LEGAL at SVR

[Al Skierkiewicz]

I am sorry you had some problem with this part. I have received a call or two on the legality of this part over the season. At Champs they will be considered legal.

[Tristan Lall]

I should mention that I was inspecting at SVR, but wasn't the LRI or the inspector described above (though I did notice and speak to someone from 766 about this issue prior to their initial inspection).

The fundamental test of legality depends on the working pressure rating of the pneumatic device. The rule isn't clear on the distinction between manifold and valve, but the manufacturer's documentation (not attached, because I don't know which version is most authoritative) implies that manifolds are included in the rating by picturing them alongside the table of specifications, with valves installed.

The relevant rules are R76 and R78:

Originally Posted by R76

All pneumatic components must be COTS pneumatic devices rated by their manufacturers for working pressure of at least 125psi (with the exception of R78-D).

Originally Posted by R78

The only pneumatic system items permitted on 2013 FRC ROBOTS include the items listed below.
A. Items available in the 2013 KOP,
...
C. Solenoid valves with a maximum 1/8 in. NPT port diameter, and a maximum Cv of 0.32,
D. Solenoid valves that are rated for a maximum working pressure that is less than 125 psi rating mandated above are permitted, however if employed, an additional pressure relief valve must be added to the low pressure side of the main regulator. The additional relief valve must be set to a lower pressure than the maximum pressure rating for the solenoid valve,
...

Of particular note, the requirement in R76 applies to every pneumatic component, except those excepted by R78-D. Valves from the KOP (including FIRST Choice) can be permitted via R78-A (in which case they must meet R76, i.e. 125 lb/in²), or by R76-D (i.e. 125 lb/in² or a relief valve). This means that—in the absence of a supplemental relief valve—every solenoid valve must be rated by its manufacturer for a maximum working pressure of 125 lb/in². (FIRST did issue a Q&A that could be read in a manner that would give a different impression—but teams have to assume that the rules take precedence.)

The inspector was right to inform you of the violation, based upon the printed rating on the SMC SY-series valve you were using (0.7 MPa = 102 lb/in²). (The Festo VUVG-series valves used by other teams were rated at 8 bar = 116 lb/in².) The burden of proof is upon the team to justify a higher rating, based on documentation. Appeal to the LRI is also allowed, and in this case, extenuating circumstances caused the LRI to rule that you (and everyone else) could use the valves.

In discussing this with the LRI, mitigating factors included the fact that FIRST had permitted these valves in the past, that the documentation was not clear on the definition of the pressure ratings contained therein (were they the limits of function, or the onset of failure?), that they were available as FIRST Choice parts (or via PDVs in the KOP, which isn't exactly the same thing), and that there was no credible safety hazard.

After the LRI made his ruling, I documented 30 robots (of 59 at the event) that had valves bearing pressure ratings less than 125 lb/in²—almost all were the SMC or Festo valves mentioned above. I did not verify which robots were carrying the requisite relief valve, but didn't see any additional relief valves on the robots I inspected in detail. Spare parts had only one relief valve to give, and that was best retained in case someone needed to protect their 120 lb/in² system.

We were also in contact with IFI, who verified that they had conducted their own tests and were willing to warrant that the valves would be safe up to 0.9 MPa = 131 lb/in² with a safety factor of 2.0. SMC also gave IFI a vague assurance about the working pressure rating, but because of several inconsistencies in SMC's product naming scheme and their published documentation (according to IFI, who heard this from SMC, the newer SYJ-series valves are printed with model numbers in the SY-series—so there are two distinct but very similar product lines with the same SY-series model numbers), it's not possible to conclusively establish the valves' performance limits from the datasheets that a team could present at inspection.

Given the rules, and the other aspects of this situation, in my (unofficial) opinion, this should be viewed as special permission to operate without the mandatory safety device, rather than a declaration that these valves are legal on their own (alternatively, they can be legal with the relief valve). I'm comfortable with that from a safety perspective, because these valves are operated at a nominal system pressure of 60 lb/in² or less, and even if overpressurized (e.g. by mechanical compression of an actuator), they will fail in very boring ways.

Note also that the rules only refer to a manufacturer's rating (as opposed to a vendor's)—this isn't fair to IFI, because their documentation and efforts to test the valves are not officially recognized by FIRST. I'd therefore consider the use of vendor's data to be another special dispensation.


The most viable long-term solution would involve FIRST improving the pneumatic constraints to tolerate this sort of issue more gracefully.


Aside: These valves don't have great information on C_v either—the flow conditions and pressure drop are not indicated. Nevertheless, the SY3xxx series valves have C_v < 0.32, according to the SMC datasheets.