Picked up a set of these Staun Tyre Deflators  –  and looking forward to getting them all set up, and using them for the first time!.  They feel pretty heavy duty – and seem pretty straightforward to set up.  Here are the instructions from the package – more or less ;^)
1. deflate a spare tire to your preferred deflation pressure.
2. with lock ring and adjusting cap wound down, screw your Staun Tyre Deflator onto the valve stem making sure it’s clean and threads are in good condition.
3. Loosen cap (anticlockwise) until deflator pops open, then immediately tighten cap to the position where air stops exhausting.
4. Turn lock ring up to adjusting cap and tighten.
Now that the deflator is set to the preferred deflation pressure, adjustments can be made if necessary at the rate of 3 psi per half turn of the adjusting cap.
If the tire pressure, and the deflator setting is within 8 psi of one another, a manual start of the deflator may be needed. Just pull the center pin up to start things up. Keep the deflators clean and dry, and do not interchange components (I wonder why?).
After tires have been deflated, remove the deflators. Don’t wheel with them on!