1 Reservoir and feeders
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.
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.
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.
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.
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:
- 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
. 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.
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:
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.