Worn out gaskets are the most commopn cause of leaky irrigation valves. They are easy to replace with common tools like a scredriver and a Crescent wrench.
There are a variety of irrigation valves in use within CHCID, and it is common to find different brands side by side on the same irrigation pipe. So make sure you know how many different types of valves you need gaskets for.
The best option is to bring a valve lid with you to the CHCID office so you can check that the gasket is the right one for your valves.
Second choice is to identify your valve so you know which gasket to ask for at the office. First question, are your risers concrete or PVC (plastic)? Valves in concrete risers are 5" in diameter, and the name cast in the lid is probably KT or Fresno. Valves in PVC risers are 6" in diameter and the common names on the lid are Fresno or Waterman.
Gaskets for Fresno and Waterman valves are available through CHCID, and can be bought at other locations like hardware stores and irrigation supply houses. KT valves are obsolete. CHCID has gaskets available that were custom made. We don't know of anyplace else you can get them.
A disassembled KT or Exeter valve. Note that the gasket is a round sheet of rubber with a hole in it, not a ring. These gaskets cost $5.00 each.
The gasket is a rubber ring in this 5" Fresno valve for concrete risers. These gaskets cost $5.00 each.
The gasket is a ring of rubber in this 6" valve used on PVC risers. The name on the top of the lid will be Fresno or Waterman. These gaskets cost $6.50 each.