Why does this backflow pressure valve constantly leak?

What is it about these backflow pressure valves that makes then blow from pressure once every couple of years?
Is there some "maintenance" I'm supposed to do to prevent it from leaking?
Do you think it would be easy to just put a pipe in its place instead?
The valves look pretty clean inside to me.
I just rebuilt the wider diaphragm part only a year or so ago.
What makes these things constantly blow every year or two?
How hard would it be you think to just bypass it?
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On Mon, 18 Jul 2016 22:33:30 -0000 (UTC), Danny D. wrote:

By way of belated update, I thoroughly cleaned out the backflow pressure valve components about a week or so ago, and the eruptions of water just stopped.
So I guess it just needed a "tune up" cleaning!
I wire brushed and dremeled out the crud, which was caked on a half millimeter thick, and that seems to be what the problem was.
I guess one of the three valves were sticking from the corrosion. SMALL:

To put it back together, I followed my own DIY from many years ago, archived over here: http://tinyurl.com/alt-home-repair
Which brings you to here: https://groups.google.com/forum /#!forum/alt.home.repair
Where I searched to find this thread from https://groups.google.com/forum /#!searchin/alt.home.repair/danny$20checkvalve$20backflow|sort:relevance/alt.home.repair/PWa8EZbbyps/PnRfJLPK7SYJ What would happen if I just bypassed this garden water check valve? 11/5/2012 by Danny D.
No sense in taking new pictures - they look almost exactly the same.

I'll let you know when it leaks next.
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