I talked with Duane and the Mac factory this morning. Duane has an Omni-turn retro fit with a Mac valve for his collet closer. His valve is a double solenoid model. The factory rep said for my application, I really did not need the double solenoid and could go with a single solenoid. The advantage for the double solenoid would be:
1. It would be a direct replacement for the original Hardinge valve
2. You would not need to hold the solenoid open the entire time you wanted the closer closed, the double solenoid model has momentary solenoids.
Disadvantage is they leak a lot more.
The advantage for the single solenoid valve is it seals better and is about half the price.
The disadvantage for the single solenoid valve is it has to be energized the entire time you want the collet closed, and it gets hotter because of this. There is a modification they do to the valve if it will be used continually energize and that is using grease to seal it instead of oil. In my application it should not be energize for long periods of time since I do not do production work. The part number for the valve I ordered is:
45A-AA1-DAAJ-1KA and price was $35.50 plus shipping. Mac does not sell direct, you have to go through a distributor. If you want the high temperature modification to the valve you add MOD 0449 to the end of the part number. It should get here Monday. Right now I am out of outputs so I will need to get my smooth stepper or Pokeys working and also write a macro to control the collet closer. I will post when I get something working.

Vince