On Tue, 06 Nov 2012 06:59:55 -0800, wrote:

There are some curious fittings on many of these backflow preventers.
I had a sprinkler guy install a new system and he said they are for
testing purposes and someday some code official might want to use
them for testing, but he'd never seen it done.

I called up Wilkins Zurn (Wilkins Water Works) technical support.
They told me those four fittings are for testing purposes, as
you had surmised.

I'm reading all I can on it from the datasheets right now since
it's a $755 part with a $55 repair kit - but, as you know,
repairing (fixing) takes more effort than simple replacement.

Wilkins Zurn 975XL Specification Sheet
http://content.zurn.com/web_document...-975XL(lg).pdf

Wilkins Zurn 975XL Maintenance Sheet
http://content.zurn.com/web_document...on/ISSM950.pdf

I wonder if there is Linux freeware for these CAD drawings?
Wilkins Zurn 975XL CAD drawings (DXL)
http://content.zurn.com/web_documents/dxf/975XL.dxf

Wilkins Zurn 975XL BIM 3d Model
http://tinyurl.com/aj8fh26