Installing a wall union for hand shower.

[piperca]

I am installing a Hansgrohe Thermobalance II shower valve to control a shower head and handheld shower. Can someone explain a straight forward way of plumbing the wall union (elbow, as I've also heard it called) for the hand shower? I am confused on how I can justify the angle of the union and keep the nipple length accurate. This is the union I will be using (part number 27454002):

http://www.hansgrohe-usa.com/ps/scaled/apb01635.jpg?w=345&h=450

Also, there are two versions of this union; one has a vacuum breaking check valve, the other doesn't. What would determine if I needed the check valve model or not?

Thanks!

[Terry]

You would install a drop ear 90 behind the wall, and then use a brass nipple through the wall to the Wall Union.
The cover of the wall union makes up for slight differences in distance.

The vacuum breaker wall union provides the most protection against cross connections.
Some handheld shower heads have breakers installed on the hose.

[jadnashua]

A vacuum breaker is required if the handheld could dangle into standing water. If it was sitting there and there was a hiccup in the water flow creating a suction, you could contaminate your drinking water from the dirty bath water. the vacuum breaker prevents that, and is required most places, and a good idea. As noted, some handhelds may incorporate them in it, so an extra, separate one isn't required. Probably safest to do it at the union, then it doesn't matter if the head is replaced sometime later with one that doesn't have one in it. Note, when the water is turned off, they usually release the water that's left in the hose that can be a little disconcerting, but is normal.

[piperca]

Thanks for your responses. I am in the midst of plumbing the valve and union. I'll update the thread once I get to the finishing of the plumbing fixtures ... maybe it'll help the next guy out.