Four Way Mixing Valve Piping

rosy

A 1.25" - 12' primary loop pumped by a 26/64 has two existing secondaries: the boiler loop where a 150 k btu operates on a 30 delta T, and a 180 degree section serving three A/H's of 70k each, and a 25k btu serving a plate H/E that serves a garage and one room downstairs with Entran 2.

A new 1.25 mixed secondary having 4 - 3/4" feeds to Grundfos 15/58 (3 spd) and 1- 1" feed to a 15/58 (3 spd) will employ a Tekmar (1.25" )722 4 way mixing valve with a Tekmar actuator likely run by a Tekmar 363. TheseHere's the questions:

1) Does it matter whether the mixed secondary headers are the same length and shape?
2) Does there need to be a certain amount of straight pipe going into and out of the 722?
3) On the same note: does making a short 90 degree turn(s) into or out of the valve matter?
4) Isn't resistance through this secondary circuit, since it's uncoupled, of minimal importance given the flow increase offered by the 722?
5) Is there a Grundfos (or any other brand) pump that offers slower pumping than 7 GPM for the flat plate H/E?
6) Do I really need a one way valve on the return side even though the grundfos come with check valves to prevent thermosiphoning as the runs all feed upper floors (10' above min.) ?