Pressure at Vent Silencers Query

[xisantos]

Good day to all. I am new to engineering field and I am very confused about pressures in Vent Silencers.

DATA:

Operating pressure (at the upstream of valve) : 25 barg
Design pressure : atm
Pressure drop : below 0.5
Pressure at diffuser : 1.5 barg

QUERIES:

1. Shall the silencers be designed at atmospheric pressure or with consideration to pressure drop? (I am confused about this one because silencer is open to atmosphere, but there is a pressure drop of below 0.5. Does this mean that the silencer is still under pressure?)
2. What will be the operating pressure and design pressure of the silencer?
3. Shall the support bracket be designed at 1.5 barg or just atmospheric? The Vendor said that the support bracket is designed at 1.5 barg. Is this common?

Your response is greatly appreciated and sorry about the questions . I am just confused.

Thanks in advance.

XiSantos