The design is based on the traditional model, but maximum capacity in a
limited space was a priority. The two sets of double-acting feeders were
mounted very close together, eliminating wasted space down the centre. Wind
entry to the top pumps is by the outside edges only, through the two slots
in each side. The bottom pump entries are underneath.
Above: The hinge blocks were made from hard-wearing beech, and
machined to the correct angle. Small wind-boxes were constructed around
them, onto which were glued the top fixed boards. Not pictured are the two
moving boards, laminated using beech for the frame and 1.5mm ply for
covering. The wind-transfer holes in the moving boards were covered with
leather valve flaps before fitting the boards. The valve leather is made by
folding the leather onto itself creating a laminated piece. This prevents
the valves curling up in dry conditions which would ruin effective sealing.
Above left: A moving board secured with nylon cord and beech
wedges. The hinge had been liberally greased for smooth running. Above
right: One side of the hinge was sealed with a strip of leather to
prevent leakage from one side to the other.
Above left: Preparation of the ribbing - four sets like this were
required for the feeders plus a larger set for the reservoir. 1.5mm ply was
used with cross-grain to prevent collapse under pressure. Above right:
calico strips were glued onto the main boards for initial fitting of the
ribbing. The strips are bias-cut (45 degrees to the warp and weft) so
both warp and weft threads cross the hinge line for strength.
Above left: The ribbing is glued behind the calico strips. Note the
hinge point a little inside the edge to allow for a quirk in the final
leathering. This picture shows the counter-bored hole to take the steel
crank pin. Above right: Leathering completed - the long sides were
done first with one piece each, and the ends were then done, also with one
piece each. On the left hand side can be seen a fine gauze patch covering
the bottom air entry holes to the lower feeder.
Having fitted the base strips to join the two sets of feeders together, the
reservoir hinge rail is fitted (above left) and manifold pieces
fitted and leathered (above right). The end reservoir calico hinge
can be seen ready for the ribbing. The opening to the right of that is the
airway from the reservoir to the outlet manifold.
Above left: The air inlet slots are covered with gauze to keep out
dust, and two braces are installed to keep the top fixed board rigid.
Above right: The steel cranks are fitted. These and the braces were
made by Bob Wallington. The length of the connecting rods are adjusted by
screwing two sections against one another. These 9mm rods are stronger than
the traditional wooden rods, and far smaller - ideal in this limited space.