Hi All,

Can anybody please enlighten me regarding double and single
check valves?

Questions:

(1) What is the difference between them, and how should I
    choose which is appropriate for any given application?
    (I know that the water regs sometimes specify which to
    use.)

(2) Every valve I've seen has a screw head on the body or a
    hex bolt head.  What for?  I presume maintenance, but
    how?

(3) Screwfix do cheapy 15mm double-check @ 2.39 (16281) and
    Pegler d-c @ 6.45 (15139), the latter being BS6282-1
    and WRAS approved, the former not.  Which would you
    buy?

Many thanks!

Ben
-- 
Ben Edgington
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