Backflow Preventer Questions

[Zoomieneumy]

Hi everyone,

Last week we had a well pump freeze that meant our pool fill supply line had no pressure for a period. When I got the well supply pump unfrozen, I came back to the house and found my Backflow Preventer spewing water (picture attached). I've found the replacement part, but want to understand more about what happened?

Why is it spewing and is it something that can be reset instead of replaced? Is it simply that there is contaminant in a component of the backflow preventer, or was there damage to the part?

What is the difference between the two preventers in the other pictures? Why the lower segment of the larger preventer, what does that component do?

If I get the replacement part, is this something that a moderately handy person can replace, or will I need to bring in a plumber to resolve the issue? Anyone have a good video of the replacement or an initial install?

Thanks in advance for the help!

Add: I should mention that our model of the Backflow Preventer is the Apollo 4A204A2F (the other pictured model below is Apollo 4A104A2F)

 

[JamesW]

 

[JamesW]

The bottom part is a vent, which is used on a “Reduced Pressure” Backflow Preventer.

 

[JamesW]

A Reduced Pressure Zone (RPZ) lets you know that the valve is working properly.

RPZ backflow preventers consist of two independent check valves.

They work like a double-check backflow preventer, but they also have an intermediate relief valve that opens to atmosphere if both check valves should fail.

If you walk up to an RPZ and no water is dumping out of the relief valve, then you know that backflow preventer is working properly.

If the relief valve is dumping out water, or spitting out small or large amounts of water, then you know that something is not right and maintenance on the valve is required