UV filter pump placement on a pond???

[Mr Cob]

Ok,

So here's what I have.

Pond/Mag 7 > Control Valve > Bio Filter > Pond

Pond/Mag 5 > (I want a control valve here, the manual says no.) > UV Filter > Pond

Pond/Mag 18 > Control valve > Main Fountain > Small fountain (the plumbing here is already down and hardlined from previous owner, the valve controls how much pressure goes to the small fountain).

Anyone see any problems here, and what's the big deal with adding a control valve on the tubing with the UV???

Thanks.