Question
QUESTION: I have a system with what looks like Hardie 700 series valves in it. Zone one is leaking from the lowest head. It looks like I have the 1.5" valve on zone one. I have found a supplier for parts to rebuild the valve at about $50.00. Would it just be cheaper to replace the whole valve? If so, what size? I only seem to find 1" valves for replacement.

ANSWER: Thanks for your question.
It was probably intentional an 1-1/2" valve was used. The flow rate (GPM)of the zone would determine whether a 1" or 1-1/2" valve would be needed. If you use a smaller valve you may find the pressure loss through the valve unacceptable. Also the closing speed will be very fast, this causes water hammer and is not good for the piping system.
Does the lowest head always leak or does it stop after a few hours? It may be just a "low head drainage" problem.

Matt

---------- FOLLOW-UP ----------

QUESTION: It appears to be leaking all the time. It is wet all the time. I never noticed that before.

Answer
It appears you got the diagnosis correct. The valve needs service. have you tried just removing the top and cleaning and flushing the valve? It may be all it needs.
You didn't say so, but I assume the valve does open and close. Just doesn't close all the way. This would indicate debris in the valve.
Good luck.

Matt