The use of ,*just*, those valves, with their attached atmospheric vacuum breakers, is now, I firmly believe, a code violation in your state. I know it is in mine,(Va.), and they are REALLY starting to enforce it! Think seriously about adding a pressure vacuum breaker device.The new Ca. law/code, requires ALL backflow prevention devices be tested annually, this means you! When, and how your district will enforce this is anyones guess. Me thinks it would be easy to add an extra duty to your water meter readers duties; ---
{Does the residence have a sprinkler system?, yes, have they submitted their annual report?, no, CHA CHING!}.
Section 13.08.110 Violation--Penalty.
A. It is unlawful for any person, firm, or corporation at any time to make or maintain or cause to be made or maintained, temporarily or permanently, for any period of time whatsoever, any cross-connection between plumbing pipes or water fixtures being served with water by the city water department and any other source of water supply, or to maintain any sanitary fixture or other appurtenances or fixtures which, by reason of their construction, may cause or allow backflow of water or other substances into the water supply system of the city and/or the service of water pipes or fixtures of any consumer of the city.
B. Any violation of this chapter shall be punished by a fine not exceeding five hundred dollars or imprisonment for term not exceeding six months or by both such fine and imprisonment; provided nevertheless, that any violation or offense may be deemed an infraction as defined by Section 19C the California Penal Code and charged as such in the discretion and at the election of the prosecuting attorney, in which event the punishment therefore shall not be imprisonment but a fine not to exceed the amount specified by Government Code Section 36900, as then in effect.
C. Every day any violation of any provision of this article continues constitutes a separate and chargeable offense. (Ord. 471 § 2 (part), 1991: prior code § 23-61)
OK, OP I'm gonna take off my tin foil hat now. Your county is probably awash with funds, and a surplus budget and would never stoop to such revenue grabbing tactics, as mine HAS. Check your water districts web site and get the facts. It would be rare that all three valves would *mechanically* fail at the same time. Every valve "eventually" fails, however I have installed at least 500 valves such as yours, and rarely have I needed to R&R any of them, over a 25 year period. Maybe you should just try cleaning them. Bear in mind the diaphram has to go back in the same way it came out, so make sure it is aligned, otherwise you could damage it with one of the screws. This is why I prefer the valve shown in your second example, the jug top just spins off, you can also manually operate it without water spitting out the bleeder. Sometimes city crews can let debris in the line, or your water may have a high mineral content. It's true that the total valve rebuilding kits are almost as much as a new valve, but unless your valve manifold is equipt with unions do you really want to cut, couple, and glue? BTW, Home despot has pre-fabbed valve manifolds with, or without valves, WITH unions, hint hint.