All pores of porous aluminium are open, the material is permeable over the entire volume. The manufacturing process of porous aluminium makes it possible to regulate the flow rate of silencers over a wide range. This results in a low back pressure (pneumatic resistance) of the silencers and a minimal impact on the operation of the pneumatic system.

The flow rate is determined by the Darcy equation:

**Q = (К×ΔP×S)/(µ×H) **

where Q is the flow rate of air, m3/s; K is the permeability coefficient, m2; ΔP – pressure drop, Pa; S – area of the porous part of the silencer, m2; μ is the viscosity of air, Pa × s; H – wall thickness of the silencer, m.

**Permeability coefficient** K (m2) for porous aluminium with different pore sizes: