The 1/2" Wilkins Model 420 pressure vacuum breaker began production in 1998 and was discontinued in 2013. The 420 was replaced with the 420XL, which is the lead free version. The 420 was designed as a freeze resistant vacuum breaker. The 420 still must be winterized as it is "freeze resistant" not "freeze-proof." The check assembly is self contained and has a replacable seat. The air inlet uses a rubber fold instead of the traditional spring inlet. In 2010, a lead free version was created. Leaded and lead free versions use the same internal parts.No special tools are required for servicing.