SMC Solenoids adequate for 125 psi - documentation provided

[Gary Dillard]

Here's the correspondence and responses I received from SMC Tech Support (I have submitted this to FIRST Q&A to verify that it is adequate):

To: techrep@smcusa.com
Subject: Solenoid valve rated pressure
I have ordered some SY3120 double solenoid valves which show a maximum operating pressure of 0.7 bar (~100 psi). I need to know if these valves have a rated pressure higher than the operating pressure, such that if my upstream pressure regulator fails they do not have to operate but they will not fail catastrophically under pressure. I need to put a pressure relief valve in the system set below the pressure rating of the lowest rated component in order to protect them (our normal operating pressure is 60 psi but pressure upstream of the regulator is 125 psi).

Thanks

Gary J. Dillard, P.E.


Gary,
We rate that at a maximum pressure of 100 psi due to the fact that the SY valve will shift automatically (no voltage necessary) at about 125 psi. At this pressure, the pilot section can generate enough force to shift without the assistance of a coil.
Regards,
Bryon Hartzog
Technical Support
SMC Corporation of America

Hi Bryon; if I understand your answer correctly, the valve is not designed to operate above 100 psi (with some margin), which is OK - we are running at 60 psi. My primary concern is catastrophic (overpressure) failure if my regulator fails - have these valves ever been tested to failure? We currently have a pressure relief valve upstream of the regulator set at 125 psi; I need to know if I need to add another pressure relief valve downstream at some pressure less than that to protect the valve from exploding if the regulator fails and the pressure goes from 60 psi to 125 psi. The rest of the components are rated at 125 psi or higher.

The application is a robot built by a high school team for the FIRST robotics competition (I am the mentor), and the rules for pneumatics have been modified this year; we've used these valves before without any problems (SMC used to donate some of them) but this year the extra pressure relief valve is required if any component is not rated at 125 psi, which is different from being operational at 125 psi.

Thanks
Gary J. Dillard, P.E.

Gary,
The valve will not catastrophically fail at or below 125 PSI due to air pressure alone. The proof pressure, according to JIS standards is 1.5 times the maximum operating pressure.

Regards,
Bryon Hartzog
Technical Support
SMC Corporation of America

Included Attachment:

[ChuckDickerson]

Good news! The GDC has answered.

[Gary Dillard]

Sweet! I presume that a copy of this thread is OK to bring; if anyone needs me to forward them a copy of the email PM me.

[Al Skierkiewicz]

Please burn that last sentence into your brain...
"Please make sure to bring a copy of the documentation with you to Inspection."

[martin417]

If you order a K version of any SMC valve, it is rated at 145 PSI. When constructing the part number, you just have to select the "high pressure" option. The part # will look something like this:

VQZ2120K-6G1-N7

This is a vqz2000 series valve with a metal seal, Cv is .3 in one
direction, .32 in the other. Max pressure 145 PSI. It has 1/4" one touch
fittings on the work ports, 1/8" NPTF on the pressure and exhaust ports
and can be mounted on a manifold. It operates on 12 volts, and has lead wires attached to the coil (no plugs)


The K indicates high pressure, or a 145 PSI rating.

[martin417]

I hope that the documentation provided by Gary is sufficient. It says that the the valve will not fail catastrophically at 125 PSI, it does not say that the valve is RATED at 125 PSI. The rule says: (emphasis mine)

All included items must be “off the shelf” pneumatic devices rated by their manufacturers for pressure of at least 125psi, and...

...Solenoid valves that are rated for a maximum pressure that is less than 125psi 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.

By the letter of the rule, if your valve is not rated for 125 PSI (any SMC valve w/o a K in the part number is generally rated at 100 PSI) you must install a regulator to reduce the pressure to below the valves rating. Since the maximum allowable working pressure is 60 PSI, you should be OK, but they could require a second regulator downstream of the first for redundancy.

It also kind of irritates me that we paid extra ($$$) and waited an extra 2 weeks to get a special version that is rated above 125 PSI so that we would be legal, and it may be unnecessary. This is a catalog option that is available to all teams, anyone could have ordered it.

[Gary Dillard]

Originally Posted by martin417

I hope that the documentation provided by Gary is sufficient. It says that the the valve will not fail catastrophically at 125 PSI, it does not say that the valve is RATED at 125 PSI. The rule says: (emphasis mine)



By the letter of the rule, if your valve is not rated for 125 PSI (any SMC valve w/o a K in the part number is generally rated at 100 PSI) you must install a regulator to reduce the pressure to below the valves rating. Since the maximum allowable working pressure is 60 PSI, you should be OK, but they could require a second regulator downstream of the first for redundancy.

It also kind of irritates me that we paid extra ($$$) and waited an extra 2 weeks to get a special version that is rated above 125 PSI so that we would be legal, and it may be unnecessary. This is a catalog option that is available to all teams, anyone could have ordered it.

Emphasis mine - that's not correct - the rule says a pressure relief valve, and as a fall back, we will be bringing an extra relief valve and a tee to set at 100 psi downstream of the regulator if there is a problem; that option is available to anyone and is what we planned to do if the GDC had ruled the other way. So if you spent extra time and money to save a few ounces of weight, that is your choice but don't get irritated.

However I understand your frustration. And if I look in the catalog at your valve it doesn't say "rated" anywhere, it still says maximum operating pressure. You could certainly infer that it must be rated above its operating pressure but it doesnt say that. Since the only difference appears to be the seal material, it makes sense that the valve may not operate and in fact may leak, but from a safety standpoint that should be adequate (remember, this depends on another component failing at the same time).

Also, the K option is not available on the SY series of valves which are the valves that FIRST had supplied for several years in the kit.

[Joe Johnson]

What is the final ruling then on the rated vs. will not catastrophically fail issue?

I am really sorry to be coming in late to the party but I just got tossed in to the mix.

By the way, I have the same issue but with a slight twist. I have a NVKF334-XXX on my desk here. I want to use it but it too is only listed as 0-0.7Mpa or 0-100psi.

What is a person to do?

Joe J.

P.S. Not to hijack this thread or anything, but can I just vent a bit. I just spent 4 hours trying to figure out the pneumatic rules for our team and trying to find a solenoid valve that is legal and does what we need it to do (yeah I know that the robot shipped last week, but for reasons beyond the scope of this discussion, my team just now discovered we don't have enough solenoids to run our robot -- our fault, I know -- and that the kit one is out of stock until the day our competition begins... ...you do what you have to do if you want to get your robot to be working on Friday morning of the competition).

So... ...I have just now gotten into the mess of that is the pneumatic rules. YUCK! If I say more it won't be nice so I will just leave it at that... JJ

[Gary Dillard]

I understand your frustration Joe.

2 things. First - R72-C says "rated" but it doesn't specify which rating (operating pressure, proof pressure, burst pressure, fatigue pressure are all defined by NFPA), so that is the only issue up for debate. I'm going with the interpretation that the documentation I have from SMC is adequate to say that these valves can be safely operated up to 125 psi. It says the proof pressure is 1.5 times the maximum operating pressure and that the valve can sustain that pressure for 1 minute and still function normally afterward.

Second - Regardless of the ruling, it doesn't make this or any valve "illegal". It just means you need to have an additional pressure relief valve downstream of the regulator, set above the regulator pressure and below the "rated" pressure (R72-C). You should already have a procedure for verifying and adjusting the KOP valve per update 11 (see rule R77, latest version), so use last year's KOP valve, dial it down to below 100 psi, put in a tee and put it in line.

[Al Skierkiewicz]

Gary and Joe,
Just to be sure R72 in REV J is this...
C. ...Solenoid valves that are rated for a maximum pressure that is less than 125psi 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.

I read and interpret that as maximum pressure not working pressure. It is clear that the valve can withstand a maximum pressure in excess of the stored pressure limit for our robot system.

Joe, see what you have been missing?

[Gary Dillard]

Ah, I missed that point. Thanks Al.