wrote:

a booster pump to my hot water system? I know I need a flange to
prevent ingress of air,

Depending on your tank layout (i.e. where it is with respect to the cold
cistern etc) you may get away without a flange. Many of the pump fitting
instructions specify an essex flange as the first choice, then surrey,
then a tee off an angled pipe from the top of the tank etc in decreasing
order of desireability. The more powerful the pump the more important
this becomes. Also if you get lots of air in the system as it is then it
is also more important.

and I need a prv to protect my shower pump

Pressure reduction valve? Depends on the way you are planning to set it
up...

Inline filters on the input would be good as well (a decent pump will
probably come with them)

(integral), and I know where I will be able to fit the pump. This is
where it gets tricky! Most of the pumps I'm looking at have 4 ends to
them, but some have 2. I will be fitting it above my tank and I
haven't got a clue which pipes I should be hooking this up to. HELP!

Below the hot water cyliner is preferable to above although it its the
distance to the water level in the cold water tank that matters most. If
this is too small you may need a "negative head" pump.

The pumps typically have 4 connections as you say, hot and cold in, and
hot and cold out. The ones with only two are designed for boosting just
a single supply only (like boosting pressure to a gravity fed hot
supply so that it can be more effectively mixed with mains fed cold (and
you *may* want a PRV on the cold mains feed there), or, a single can be
used after the shower mixing valve to pump the blended water to the
shower head.

The type with four connections are designed to boost low pressure hot
and cold at the same time. To install these you take a hot feed to one
inlet from your hot cylinder (via the flange or whatever), take the cold
feed from a dedicated pipe from the cold tank to the other. Then take
the outputs to the shower, or other taps as required.

--
Cheers,

John.

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