Seeking SMC Pneumatics Advice

[Tristan Lall]

Originally Posted by IndySam

Cv will vary according to the pressure used and even temperature, it must be calculated for every given situation. It is a poor value to use for our purposes.

I like the idea behind using C_v, but I don't like the way the rules implement it (it's under-specified), and I don't like the way many valve manufacturers are vague about it (not specifying the test conditions, not specifying the ratings independently for different products in the same line, etc.).

The C_v ratings can be measured according to several standards, which are not necessarily equivalent. (A couple articles in Machine Design describe the controversy: see the accusation and the rebuttal.¹)

¹ This is actually the first time I'm seeing the rebuttal article, so I'm not going to reply with what I thought I was going to write about the merits of the different standards. This requires more research—but maybe someone else should take that project on, and report back the bottom line on the appropriateness of using different standards to find C_v.

[Daniel_LaFleur]

Originally Posted by IndySam

Cv will vary according to the pressure used and even temperature, it must be calculated for every given situation. It is a poor value to use for our purposes.

Cv does NOT change due to pressure or temperature, in fact the pressure and temperature are standardized (60'F and 1 PSI) as is the medium (water). Cv is a constant for a given valves geometry (orifice size, orifice geometry, mass flow diruption and eddies, etc) and can be used to calculate the mass flow rate through a valve.

Flow rate (mass flow) does change with pressure and temperature( and the medium flowing through the valve).

[David Doerr]

It's been a while since I began this thread and I'm following up to let you know what we decided to buy and why. Our intention was to outfit our rookie team with pneumatics so we had hardware to learn with before the start of the upcoming season in January.

There's a lot of detailed information available on SMC products and it took some effort to wade through and understand everything. A wide range of options are available so the purchaser can choose almost exactly what is needed - I like that.

I looked into buying Festo products since that is what has been provided in the KOP and we can be more certain that Festo components will pass inspection. From my novice vantage point, Festo seems to be the premier pneumatic valve supplier compared to SMC. Festo also looks to be just as configurable as SMC and you can mount Festo valves on a manifold - which we would like to to. However, Festo is a lot more expensive than SMC and harder to get.

I went through the process of contacting Festo with our team number and they said they would set me up so I could purchase directly from the Festo website, but Festo has not followed through with that so far.

...So I decided to buy SMC "body ported" valves because:
- output ports are on the top of the assembly for easy access
- electrical connnections also on the top of the assembly for easy access (option M)
- allows several valves to be mounted to manifold with a common input port

I bought:

2 single solenoid valves, SY3120-6MZ-N7
2 double solenoid valves, SY3220-6MZ-N7
6 station body ported manifold, SS5Y3-20-06-00T
2 blanking plates, SY3000-26-9A (to plug the two vacant spots in the manifold)
6 one-meter-long wires with connectors, SY100-30-4A-10 (to avoid having to splice wires)

I ordered the parts from coastpneumatics.com. Some of the items were not in stock and had to be ordered from Japan. (I knew this when I placed the order.) I was quoted a six-week lead time to when the parts would arrive at Coast in CA. I placed the order on August 21 and received the last of it on September 7. The parts were shipped by UPS 3-day select even though I paid for UPS ground from CA to MI where we live. Great service from Coast Pneumatics...

Team member Nathan assembled our valves and manifold. We haven't tried to use the valves yet - that will have to wait a little longer while we work on our software.