288
8 Secondary Ventilation
Fig. 8.4 Layout of the
mixed ventilation scheme of
development end
returns through the gallery. Although this system combines many of the advantages
of the two previously mentioned systems it also has many of their disadvantages,
and in addition, its installation is more complex and more expensive than either of
them. The system uses either rigid ducts or steel reinforced canvas ducts.
8.2.4 Overlap System
In an overlap ventilation system two fans are used, with one of them placed very close
to the active face. There are many possible configurations, but the most frequently
used is shown in Fig. 8.5. Here, the forcing fan is closest to the face, while the
Fig. 8.5 Recommended
layout of an overlap
ventilation system for a
development heading
≤5√S
x √S
8 Secondary Ventilation
Fig. 8.4 Layout of the
mixed ventilation scheme of
development end
returns through the gallery. Although this system combines many of the advantages
of the two previously mentioned systems it also has many of their disadvantages,
and in addition, its installation is more complex and more expensive than either of
them. The system uses either rigid ducts or steel reinforced canvas ducts.
8.2.4 Overlap System
In an overlap ventilation system two fans are used, with one of them placed very close
to the active face. There are many possible configurations, but the most frequently
used is shown in Fig. 8.5. Here, the forcing fan is closest to the face, while the
Fig. 8.5 Recommended
layout of an overlap
ventilation system for a
development heading
≤5√S
x √S