So that others can find it more easily, here is a step-by-step
pictorial DIY showing each step in my repair today of my
1" ID Wilkins Zurn 975XL Backflow Preventer, thanks to your
help at alt.home.repair.
STEP 0: Shut inlet & outlet valves & open #2,#3 & #4 test ports
STEP 1: Repair & clean the #1 check valve on top inlet
STEP 2: Repair & clean the #2 check valve on bottom outlet
STEP 3:Repair & clean the relief valve on the side inlet
I found all the parts inside the three valves in excellent condition
as you had suggested it would be - but I replaced them all anyway.
The key problem I saw was the #2 check valve was stuck in place
due to light-green corrosion inside the brass cap cavity.
Also there was light-green corrosion in all cavities, which I
painstakingly wire brushed out - as that was the key issue.
On a scale of 1 to 10, this is an easy 1. No surprises. No special
tools. It took me about three hours - one hour for the #1 check
valve on the top inlet, another hour for the #2 check valve on the
bottom outlet, and another hour for the relief valve on the inlet.
It should take you about a half hour in total - maybe 45 minutes,
depending on how well you wish to clean out the green corrosion.
I took my sweet time.
Below is a quick DIY with photographs for the $755 1-inch ID
Zurn Wilkins 975XL Reduced Pressure Principle Backflow Preventer
after detailing the 11-piece Wilkins Water Works RK34-975XL $43.20
repair kit (855-663-9876) and assembly instructions.
HERE ARE THE KEY REFERENCES:
Wilkins Zurn 975XL Specification Sheet
Wilkins Zurn 975XL Maintenance Sheet