It is very desirable to place an efficient strainer on the suction pipe
of a pump where there is the least suspicion that the water contains
any sediment or floating matter.
Several of these useful pump attachments have been already shown,
connected with pumps, in previous sections of this work, but a few more
are here added.
Fig. 597 exhibits a cross section of a strainer of large capacity of
long and satisfactory use. It has a semi-cylindrical vessel located
in one side of the side pipe. Holes are drilled through the flat side
extending across the diameter of the side pipe; any floating matter
which will not pass through the holes collects in this strainer vessel
and may be easily removed.
[Illustration: FIGS. 597 AND 598.]
Fig. 598 represents a longitudinal section of this strainer. The top of
the chamber is covered by a bonnet secured by a claw having one bolt,
so that by unscrewing this bolt the claw and bonnet may be unfastened
and the settling chamber with perforated plate withdrawn.
A suction valve with double strainer is represented by Fig. 599, in
which the outer screen is raised for cleaning. In lowering, it is
guided to its place by the cage around the foot valve chest, as will be
seen in Fig. 600, which is a sectional view of this same valve. The
suction pipe extension enables the pump to draw water when its surface
has fallen below the top of strainer and also below the foot valves.
This is often a great advantage where water is scarce and every gallon
is needed.
_This foot valve is a “double clack”_ hinged in the center. There
are no openings or perforations in the bottom plate. Fig. 601 is a
very convenient form of strainer for large pipes and where it is an
advantage to have the strainer in the engine-room or near the pump.
This strainer, like Fig. 597, can be lifted out for cleaning by
removing the claw and bonnet. The chamber may be washed out by removing
the plug at the bottom.
[Illustration: FIG. 599.]
[Illustration: FIG. 600.]
A most convenient vacuum chamber and strainer is represented in Fig.
602; it is located near the pump. By removing the suction chamber the
basket or strainer may be lifted out by the handle under the arrow.
The outlet is generally attached directly to the pump. The pump may be
charged by removing the “priming plug” and inserting a hose, with water
turned on.
_Steam boiler feed water impurities_ consist mainly of chemical
substances which are unaffected—as may be readily supposed—by
mechanical devices just described; these impurities are largely
invisible being dissolved in the water and hence, also, considering
their variety, are most difficult to contend with. How to avoid the
actual evils arising from the presence of foreign matter in feed water
is of the first importance in steam economy; enormous losses of money,
danger to life and property are involved in it. It has been said that
there are more millions of treasure to be made by properly “treating”
the water which enters the steam generators of the world than can be
extracted from its gold mines.
[Illustration: FIG. 601.]
[Illustration: FIG. 602.]
NOTE.—Strangely, investigation has proved that water of this purity
rapidly corrodes iron, and attacks even pure iron and steel more
readily than “hard” water does, and sometimes gives a great deal of
trouble where the metal is not homogeneous. Marine boilers would be
rapidly ruined by pure distilled water if not previously “scaled”
about 1/32 of an inch.
To deal properly with this subject the science of chemistry must
be largely drawn upon; chemically pure water is that which has no
impurities, and may be described as colorless, tasteless, without
smell, transparent, and in a very slight degree compressible, and, were
a quantity evaporated from a perfectly clean vessel, there would be
no solid matter remaining. Now, in dealing with the impurities inside
a boiler, it is to be observed _that in no sense do they change the
essential nature of water itself_. The impurities are simply foreign
bodies, which have no legitimate place in the boiler, and are to be
expelled as thoroughly as possible.
The chemical substances to be eliminated are indicated in the note
below. Water, on becoming steam, separates from the impurities which it
may have contained, and these form sediment and incrustation. This is
an important fact.
_Corrosion_ is simply rusting or wasting away of the surfaces of the
metals. Incrustation means simply a coating over.
Several approved recipes and “notes” of instruction for removing
sediment and incrustation from steam boilers will be found near the
close of this volume.
NOTE.—Analysis of average boiler scale. Parts per 100 parts of
deposit.
Silica .042 parts
Oxides of iron and aluminium .044 „
Carbonate of lime 30.780 „
Carbonate of magnesia 51.733 „
Sulphate of soda Trace
Chloride of sodium Trace
Carbonate of soda 9.341 „
Organic matter 8.060 „
------------
Total solids 100. parts
The percentage only of each ingredient the scale is composed of is
given, as it cannot be told how much water was evaporated to leave
this amount of solid matter.