THE ESSEX FIELD CLUB,
121
valves which drain the reservoir when necessary, and which are capable
of passing no less than 35,000,000 gallons of water in 24 hours, when all
the valves are open.
Mr. Wood here read an interesting account of the fauna of this and the
older reservoirs in the Lea Valley, which is printed in full on Page 69.
The entire length (some 2 miles) of the Reservoir embankment was
then followed, a profusion of wild plants being noted on the earth-slopes,
and characteristic aquatic plants, such as Sparganium ramosum, Alisma
plantago, Scirpus, Sagittaria, etc., being observed in the "diversion-stream"
which runs alongside the reservoir at the foot of the embankment, speci-
mens of which were gathered for further study. Many Sand Martins were
hawking over the stream, and speculation was aroused as to where they
secured nesting facilities, it being suggested as not improbable that they
utilised the drainage-holes left in the stone embankments of the stream,
in default of other accommodation. A Whinchat was sighted, and a
Great Crested Grebe, but the day, and ths necessarily rapid progress of
the party, were unfavourable to bird observation, and Mr. Wood's alluring
list of the bird-frequenters of the Reservoir had perforce to be taken
on trust.
On reaching the northern end of the Reservoir, the Pumping Station
at Enfield Lock was inspected, with its 5 great Humphrey Pumps, four of
these being capable each of pumping 40,000,000 gallons of water into
the Reservoir, and the fifth 20,000,000 gallons, a total of 180,000,000
gallons in 24 hours ! By favour of Mr. Wood, one of the larger pumps
was set. in action for the benefit of the party, and the enormous volume
of greenish water welling up from the trunk pipe at each stroke of the
pump was a most impressive sight. Mr. Whinnerah, the Resident Engin-
eer, explained the mechanism of the pumps to interested members of the
party. Mr. Wood kindly supplies the following account of these mighty
engines.
The total area of the Metropolitan Water Board's storage Reservoirs
in the Lee Valley, between Walthamstow and Enfield Lock, is about
905 acres and their capacity some 5,541,000,000 gallons. The latest
and largest Reservoir (the "King George") has an area of about 425
acres and contains 3,073,000,000 gallons, its circuit being about 41/2 miles.
The King George Reservoir is filled from the River Lee just below
Enfield Lock. The pumping plant consists of 5 Humphrey Gas Pumps,
with a total of 1,350 horse power.
As now installed, the pumps work on the four-stroke cycle as follows
Starting with the working stroke, there is the ignition of a combustible
charge compressed into the top of the pump cylinder. This charge is
expanded down to a little below atmospheric pressure, which results
in a charge of water and a charge of scavenging air being drawn in through
automatic valves. At the same time water is delivered through the
discharge main to the high level reservoir. This working stroke is followed
by a return stroke of the water column, which first expels the products
of combustion through the exhaust-valves. These valves are then
closed by the impact of the moving water and the air entrapped is com-
pressed into the head of the cylinder, where it forms an elastic cushion,
which gradually brings the moving column of water to rest. The re-