shuttle valve piston Gtol

[djhurayt]

Any suggestions on how best to control the six ground diameters of a shuttle valve piston.
The perfect part would have:
1) all the diameters exactly the same
2) all the diameters concentric with each other

Thoughts:
1) let one end be datum A, the other datum B and a callout for total runout of each surface relative to A-B
2) continuous feature (but not sure of the details of how to apply)
3) one end be the a single datum and all other surface either controlled with total runout or true position

Not a lot of experience with multiple boss precision shafts and thought or direction appreciated

edit:
forgot to add ASME

 

[CheckerHater]

Something to consider:

"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future

 

[djhurayt]

Thank you, that is the image I was looking for but could not find.

Is that from Alan Krulikowski's book (which I don't have with me)?

 

[chez311]

If as you say all 6x diameters ride together on the same surface, then I don't think choosing one or two of them as a datum feature to control the rest is a good idea, and it doesn't reflect design intent.

My vote would be for a continuous feature <CF> callout. Alternately control of coaxiality of the diameters could be achieved with something similar to Y14.5-2009 fig. 4-24 wtih position. I believe these two would achieve a very similar end result with minute differences.

Note that use of <CF> has been expanded in the 2018 version as the committee has realized it is a useful control.

 

[chez311]

Just to add to the case for <CF> in your application you may want to control form more tightly across all 6x diameters together (instead of individually), especially since they all presumably ride on the same surface. <CF> combined with cylindricity will allow you to do this, and I think its a better solution for your application than position.

Tec-Ease has a tip from the late Don Day which explains this, and is actually very similar to the part you included in your OP (shuttle valve).

Tec-Ease Tip Video Link