What the parts of the breathers do (helm and tank) is to slow down your rate of air consumption. So if you put on the helm, it slows by
x; if you put on the breather, it slows by
y; and if you put on both, it slows by
z, which may be greater than, less than, or equal to
x + y. I'm sure Radek can confirm the exact details
Leastways, that's how I understand it.