Why does this piping diagram is showing expansion tank on discharge side of circ?

Mjplumbing

Hey everyone, Take a look at the link I attached and notice how the expansion tank is drawn on the discharge side of circulator. I am familiar with the Point of not pressure change on the system and for the life of me cant figure out why the manufacture show to install it this way? especially with PRV to fill the system installed directly behind circulator inside the unit. Please let me know thoughts on this, Im thinking its just drawn incorrect..

neilc

head scratcher

hot_rod

the notes mention a circulator in the air handler, it could be pumping way.

HVACNUT

The diagram doesn't show where the Naviens internal circulator is, but I think it's on the return. 
Regardless, unless the air handler is right next to the boiler, I would still pipe it Primary/Secondary.

Mjplumbing

Navien has a separate drawing for an application with a pump inside the AHU

hot_rod

a small hydraulic sep would offer air, dirt, mag, and hydraulic separation, as another good option.

Mjplumbing

HVACNUT said:

The diagram doesn't show where the Naviens internal circulator is, but I think it's on the return. 
Regardless, unless the air handler is right next to the boiler, I would still pipe it Primary/Secondary.

its on the supply for sure