Tímarit Verkfræðingafélags Íslands - 01.05.1947, Side 18

40
TÍMARIT V.F.Í. 1947
day-time mainly, but the pumps work all 24 hrs. The
tanks thus function as a reserve.
Also the pressure in the town is equalized to a great
extent by means of this.
The altitude of the tanks permits gravity flow to
the pipe system in town. However, in case of maximum
use, a boosting pump station built in the line
leading from the tanks is operated. This is auto-
matically controlled by a manometer in town. This
reserve station has three pumping units, one for each
line and one for reserve. The pumps are driven by 75
H. P. electric motors. Each pump delivers up to 250
1/sec; the units combined are capable of increasing the
head 10—20 m. The double line from the tanks to
the town is made of 16 inch. steel pipes, a distance
of 900 m.
The water system in town through the streets is
about 40 km, made of 1 to 18 inch. pipes. It has about
300 closing valves, also security valves (the same as
main water line). The branches to the houses from the
street-lines are mainly of %—1 inch. pipes, out-of-
door house-lines being about 21 km.
Insulation.
Insulation is of the greatest importance due to the
distances. This differs in the various parts of the
system.
The selection of material was made with regard to
three main factors, insulating capacity, cost and dura-
bility, since ground water and leakage are liable to
effect damages both on insulation and the pipes.
To minimize damages of this kind most out-door
pipes rest on iron supports in closed concrete channels
which slope sufficiently for drainage through special
drains at the end of the slopes. Leakage was pre-
vented by welding the pipes together wherever
possible.
However, insulating material had to be chosen
with regard to leakage and moisture. Numerous
insulating materials were tried out. The material
selected for the widest lines was a double cover of
a special turf, that for the urban system porous
lava slags filling the concrete channels around the
pipes.
House-lines are insulated outdoors by glass-wool,
protected from ground water by tarred paper and
bitumen sheets melted together on the edges.
In-doors, felt wrapped in linen was used. Around
valves and expansion joints and in house-line boxes,
ropes and mats of glass wool, the latter coated with
asphalted paper, were used.
The cistern at Reykir is insulated by turfy ground.
The concrete tanks on Öskjuhlíð are coated inside
with 15 cm thick pumice slabs, then concrete coating,
three layers of linen specially aspalted to withstand
the heat and finally 5 cm thick reinforced concrete
to protect the linen. The house-lines are the narrowest
in the system, and consequently need the best of
insulation, and for the same reason the street-line
channels for 1 and 6 inch lines are of the same width.
The insulation used has proved to be good, so that
in the coldest part of the winter the temperature drop
is only 2—3° C from Reykir to the tanks on Öskju-
hlíð and 3—4° C from there to the farthest home
using this heating system.
Expansion and contraction.
The heating system is exposed to great changes in
temperature. Therefore allowances must be provided
for thermal expansion and contraction, this being
especially so for the pipes that lengthen about 1
mm per meter when the hot water is put on.
For this reason expansion joints are inserted at
proper jntervals, the pipes being fixed firmly
between the joints, which are of various types.
For the main line the joints are of the slip type
with chromium plated steel slips.
In the urban system short corrugated pipes of three
different types are used, two of these being of steel
and one of copper protected by cast iron rings.
The walls of these pipes are with flexible trans-
verse waves, but to minimize resistance against flow
and to prevent stones settling in the waves, a steel
pipe fastened at one end covers the inside of the joint.
The number of the waves in each unit varies
according to how great a movement it is to stand.
Above mentioned expansion joints are made for
lengthwise movements only, therefore flexible pipes
made of copper alloy (tombak), which bend easily,
are inserted. They are put in the narrowest street-
lines and many places where a house-line and movable
street-line are connected at right angles.
The tombak pipes in the house-lines are of two
types. One can stand about 5 cm bend, the other 10
cm bend. The less flexible one is used where the
distance from anchored point in the street-line to
the house-line connection is less than 50 m, the
other where the distance is 50—100 m.
In the urban system all crossings and bends are
anchored and also at 100 m intervals on straight lines.
On the main line this is at 200 m intervals. The
anchors are of different sizes and types, depending
on width of pipe and magnitude of the force, which
in places amounts to about 23 tons.
In order to prevent side strain on the expansion
joints the streetlines are laid on iron supports to
prevent sagging.
Iron bars prevent side bends. In the main line roll-
er bearings are used instead of iron supports, side
supports being unnecessary.
The expansion of the house-lines is cared for by
zigzag bends of the pipes — the insulation coating