594

THE COLLIERY GUARDIAN.

March 20 1913.

compressors, was to pump the air through a nozzle,
measuring the pressure before and after. If they
measured volumetric efficiency from the indicator
diagram, they did not take into consideration the rise in
temperature of the air in passing into the cylinder. This
might be very large, although it was not shown on the
diagram at all. If the air, in passing through the inlet
ports, was warmed up, they had a temperature inside
the cylinder which was very much higher than the
atmospheric conditions ; and that increased temperature
increased the volume of air without a proportionate
increase of waste of air. In addition to that rise
of temperature which was caused by warming, there
was another rise which was caused by mixing with
the air that had re-expanded from the clearance spaces,
and any additional high-pressure air which might
have leaked past the piston rings or delivery valves.
Mr. Walker had made no reference in his paper to the
Koster compressors, which had found very great favour
on the Continent, and which, he believed, were now
being manufactured in this country. The section of
the paper in which he was most keenly interested was
that dealing with turbo-compressors. Nearly all the
principal makers of reciprocating air-compressors on the
Continent were now taking up the manufacture of
machines of this sort. For South Africa, machines had
recently been ordered for units of over 10,000-horse
power, a size that had not been approached in any
reciprocating compressors.

Dealing with the cooling arrangements of turbo-
compressors, Mr. Davis said the more they were cooled,
and the lower the exit temperature, then the lower the
pipe losses due to radiation. It was rather important
that the cooling spaces of these turbo-compressors
should be quite accessible.

The author described the turbo-compressor manufac-
tured by the A.E.G. Company as an axial-flow machine.
He (the speaker) thought that perhaps this term was a
little misleading, as the air, in passing through the
impellers, of course passed in a radial direction.
The term “ axial flow ” was used originally for the
blastfurnace blowers manufactured by Messrs. Parsons,
where the air flowed in a strictly axial direc-
tion from inlet to outlet. The design of the
impellers for turbo - compressors was a matter of
very great importance. They could not get away
from the one-sided nature of the impeller, but he
thought the thing to be aimed at in compressors of this
sort was an impeller which was solid in construction.
The author mentioned figures in regard to the consump-
tion of cooling water for turbo-compressors. He (the
speaker) had always found a very good rule to be that
| per cent, of the air volume should be used in the form
of cooling water when the temperature of the cooling
water- was above 60 degs. Fahr., that quantity being
doubled when the temperature of the cooling water was
raised to 80 degs. In actual figures, this meant about
2,000 to 4,000 gallons of cooling water per hour per
1,000 cubic feet of free air compressed per minute.
The influence of output on the speeds of turbo-com-
pressors was, of course, very marked, and such machines
for small output at high speeds were very undesirable.
He thought the limits which the author had given were
rather on the small side. Personally, he should not care
to advise anyone to instal turbo - compressors for
pressures up to 70 or 90 pounds to the square inch of a
capacity lower than 4,500 to 5,000 cubic feet. The
question of oil in turbo-compressors was of very great
importance. Not only did they save in consumption, but
they also reduced the danger of explosions and of the
emission of noxious gases underground if the oil had
become decomposed.

The discussion was then adjourned to the next
meeting, the President suggesting that if any gentle-
men present had any remarks which they had intended
to deliver that afternoon, they should write them out
and forward them to the secretary in the meantime.

[Our readers may be referred to a letter on the subject
of this discussion, which appears in our correspondence
columns this week.—Ed. C.G.]

Hull Coal Exports.—The official return of the exports of
coal from Hull for the week ending Tuesday, March 11,
1913, is as follows: — Antwerp, 812 tons; Amsterdam,
2,429 ; Alexandria, 4,163 ; Algiers, 256; Bahia Blanca,
3,500 ; Bandholm, 1,920 ; Barcelona, 1,322 ; Brunsbuttel,
2,614; Buenos Ayres, 3,000; Bremen, 1,316; Christiania,
835 ; Calais, 1,987 ; Copenhagen, 100 ; Drontheim, 49 ;
Eugene, 1,841; Fecamp, 332 ; Genoa, 2,372 ; Gothenburg,
204 ; Harlingen, 1,030; Hamburg, 5,441; Konigsberg, 488 ;
Karachi, 200; Kiel, 1,033; Leghorn, 807; Malmo, 431;
Monte Video, 6,081; Newfairwater, 155; Naples, 1,215;
Oxelosund, 7,033 ; Palermo, 3,194 ; Reval, 2,602 ; R men,
4,576 ; Rsykj tvik, 1,421 ; Riga, 494 ; Rotterdam, 4,771;
Stege, 818 ; Syracuse, 2,126 ; Stockholm, 1,551 ; Venice,
887 ; Wyk, 108 ; Ystad, 952 ; Zeebrugge, 2,195 ; total,
78,666 tons ; corresponding period last year, 23,164 tons.

THE HUMPHREY PUMP.

By far the most interesting feature of the new
Chingford reservoir of the Metropolitan Water Board
is the new type of pumps by which this reservoir is
to be filled with water from the River Lea. The
work of replenishing the water in the Chingford
reservoir involves some special considerations on
account of the nature of the flow of the River Lea. This
river is undergoing a marked change in its character by
reason of drainage works in the upper valley. As a
consequence, the floods in the Lea valley are not only
higher than formerly, but last for a shorter period. It
is stated that the flood period has been reduced to one-
third of its former duration, and as it is necessary in a
scheme of this character to impound as much flood
water as possible, the kind of pump selected for this
purpose must be chosen with special regard to the
requirements of efficiency and economy. The main
desiderata of a pump for work of this nature, dealing
with a large quantity of water at a low lift, are readily
defined. Reciprocating pumps are at once ruled out by
reason of their capital cost and moderate efficiency under
the circumstances of low lift. Centrifugal pumps, also,
although quite capable of performing the required work,
possess disadvantages in the matter of efficiency; but

Fig 1.

■Ji.'

J

I’

JI

Fig. 2.—Humphrey Pump: Combustion Chamber for the 40,000,000 gallons
per day Pump at Chingford.

View showing ports for scavenging valves (end), admission valves and exhaust valves (centre).

centrifugal pumps would probably have been adopted
had not Mr. H. A. Humphrey, at a most propitious
moment, been in a position to demonstrate the remark-
able results which he had obtained with his recently-
invented internal combustion pump of the explosion
type, using producer gas as fuel.

Principle of the Humphrey Pump.—The Humphrey
pump is intended for pumping liquids, and employs the
principle of internal combustion. The pump is suitable
for working with producer gas, suction gas, lighting gas,
petrol, or paraffin, and the thermo-dynamic cycle on
which the pump works has a greater efficiency than the
Otto cycle. There are no moving parts except the
valves, and the use of a flywheel is not necessary, since a
column of water, forming part of the water pumped,
acts as a reciprocating flywheel.

The water column, which also acts as a piston, has
four unequal strokes, such as theory requires when
expansion is carried to atmospheric pressure. These
strokes are—a long stroke during combustion and
expansion, another long stroke during exhaust, a shorter
stroke during suction, and a still shorter stroke during
compression. There is no valve across the discharge

pipe at any point, so that the water has a free passage
from the explosion chamber to the water tower whence
the water is led away at the higher level.

The action of one of the simplest types of pump can
be best explained by reference to the accompanying
drawing:—The pump proper is built up from three
main castings. C is the combustion chamber, connected
by means of the bend B to the water valve chamber W,
the discharge pipe D and thus to the water tower W T.
The suction tank S T embraces the valve box chamber,
as shown, so that there is a free access of water to all
the water valves V. These water valves are plain
mushroom or clack valves, opening inwards, and held
on their seats by light springs. In the top of the
combustion chamber are fitted an inlet valve A and an
exhaust valve E. A simple interlocking gear is arranged
between these two valves so that when valve A
opens and closes it locks itself shut and releases the
valve E, and when valve E opens and closes it locks
itself shut and releases valve A. Consequently each
time that suction occurs in the chamber these valves
open in turn.

Imagine a charge of gas and air to be compressed in
the top of chamber C and fired by a sparking plug
which projects through the top casting. All the valves
are shut when explosion occurs, and the increase in
pressure drives the water downwards in the pump and
sets the whole column of water in the discharge pipe in
motion. The column of water attains kinetic energy
while work is being done upon it by the expanding
gases, so that when these gases reach atmospheric
pressure the column of water may be moving at, say,
6 ft. per second. The motion of this column of water
cannot be suddenly arrested, hence the pressure in C
tends to fall below that of the atmosphere, the exhaust
valve E opens, and also the water valves V. Water
rushes in through the water valves mostly to follow the
moving column in pipe D, but partly to rise in chamber
0 in an effort to reach the same level inside the chamber
as exists in the suction tank. When the kinetic energy
of the moving column has expended itself by forcing



water into the water tower, it comes to rest, and, there
being nothing to prevent a return flow, the column
starts to move back towards the pump and gains velocity
until the water reaches the level of the exhaust valve,
which it shuts by impact. A certain quantity of burnt
products is now imprisoned in the cushion space, F,
and the energy of the moving column is expended in
compressing this gas cushion to a greater pressure than
that due to the static head of the water in water tower
W T. Hence a second outward movement of the
column results, and when the water reaches the level of
valve E the pressure in the space F is again atmospheric,
and further movement of the water opens valve A
against a light spring and draws in a fresh charge of
gas and air. If there were no friction the water would
fall to the same level as that from which the last upward
motion started, but the amount of combustible charge
drawn in is slightly less than this movement would
represent. Once more the column of water returns
under the water tower pressure and compresses the
charge of gas and air, which is then ignited to start a
fresh cycle of operations.

The ignition is timed by a small apparatus somewhat