Encyclopaedia Britannica > Volume 15, PLA-RAM

Vorw'*
F U M [ 661
the workin'j-barrel of the pump, ^hit fimtch has a
groove round it. Tire re is another flaneh Uv bdow,
by which this hollow cylinder is fattened with bolts to
the lower end of the pitton, reprefented in hg. 23.
This confifts of a plate CD, with a grooved edge fimi-
lar to AB, and an intermediate plate which forms the
feat of the valve. The compofition of this part is bet¬
ter underttood by infpedbing the figure than by any
defeription. The pitton-rod HL is fixed to the tipper
plate by bolts through its different branches at G> G.
This metal body is then covered with a cylindiical bag
of leather, fattened on it by cords bound round it, filling
up the grooves in the upper and lower plates. The
operation of the piilon is as follows.
A little water is poured into the pump, which gets
paft the fides of the pifton, and lodges below in the
fixed valve. The pifton being puttied down dips into
this water, ami it gets into it by the valve. But as the
pifton in defeending compreffes the air below it, this
compreffed air alio gets into the inttde of the pitton,
fwells out the bag which furrounds it, and compreffes it
to the fides of the vyorking-barrel. When the pifton is
drawn up again, it mutt remain tight, becaule the valve
will fhut and keep in the air in its moft compreffed
ftate ; therefore the pitton mutt perfonn well during the
fudftion. It mutt a£t equally well when puttied down
again, and adling aa a forcer ; for however great the
refiftance may be, it will affoft the air within the piftou
to the fame degree, and keep the leather clofe applied
to the barrel. There can be no doubt therefore of the
pifton’s performing both its offices completely ; but we
imagine that the adhefion to the barrel will be greater
than is neceffary; it will extend over the whole fur-
face of the pitton, and be equally great in every part of
its furface ; and we fufpedt that the fridfipn will there¬
fore be very great. We have very high authority for
fuppofing that the adhefion of a pitton of the common
form, carefully made, will be fuch as will make it per¬
ils dtfifls. fcdfly tight ; and it is evident that the adhefion of Bc-
lidor’s pifton will be much greater, and it will be pro¬
ductive of worfe confequences. If the leather bag is
worn through in any one place, the air efcapes, and
the pifton ceafes to be compreffed altogether; whereas
in the common pirton there will very little harm refult
from the leather being worn through in one place, ef-
pecially if it projeCt a good way beyond the bafe of the
cone. We ftill think the common pitton preferable.
Belidor’s pifton would do much better inverted as the
pifton of a fucking pump; and in this fituation it would
be equal, but not fuperior, to the common.
Btlidor dtferibes another forcing pifton, which he
had executed with fuccefs, and prefers to the common
wooden forcer. It confifts of a metal cylinder or cone,
having a broad flanch united to it at one end, and a fi-
milar flanch which is ferewed on the other end. Be¬
tween thefe two plates are a number of rings of leather
ftrongly compreffed by the two flanches, and then turn¬
ed in a lathe like a block of wood, till the whole fits
tight, when dry, into the barrel. It will fw’ell, fays he,
and foften with tire water, and withftand the greateil
preffures. We cannot help thinking this but an indif¬
ferent pifton. When it wears, there is nothing to
fqueeze it to the barrel. It may indeed be taken out
and another ring or twro of leather put in, or the flanch¬
es may be more ftrongly ferewed together ; hut all this
1
P U M
Pump,
—-v—
59
56
57
Another by
the fame
author.
. 58
©hied ions
to it.
may be done with any kind of pifton } and this has
therefore no peculiar merit.
The following will, we prefume, appear vaftly pre-^norher
ferable. A BCD (fig. 24.) is the folid wooden or metal recom-
block of the pifton; LF is a metal plate, wliich is turn- mended as
ed hollow or ditti like belowr, fo as to receive w ithin it referable,
the folid block. The pifton rod goes .through the
whole, and has a {boulder above the plate EF, and a
nut FI below. Four fcrevv-bolts, fuch as i /•, / m, alio go
through the whole, having their heads 1, m funk into
the block, and nuts above at /, /. The packing or
fluffing, as it is termed by the workmen, is reprefented
at NO. This is made as folid as poffible, and generally
confifts of foft hempen twine well foaked in a mixture
of oil, tallow, and roiln. The plate F.F is gently ferew¬
ed down, and the whole is then put into the barrel,
fitting it as tight as may he thought proper. When it
wears loofe, it may be tightened at any time by ferew-
ing dow n the nuts i /, which caufe the edges of the ditti
to fqueeze out the packing, and comprefs it againft the
barrel to any degree. g0
The greateft difficulty in the conflrudlion of ^_piflon Difficultiss
is to give a fufficient paffage through it for the water, ’V conf|.ruc*
and yet allow' a firm fupport for the valve, and fixture
for the pifton rod. We fhall fee prefently that it oc- 1
cations a conliderable cxpence of the moving power to
force a pifton with a narrow perforation through the
water lodged in the w’orking barrel. When we are
raifing water to a fmall height, fuch as 10 or 20 feet,
the power fo expended amounts to a fourth part of the
whole, if the water-way in the pifton is lefs than one-
half of the fedlion of the barrel, and the velocity of the
pifton two feet fer fecond, which is very moderate.
There can be no doubt, therefore, that metal piflons •
are preferable, becaufe their greater ftreugth allows
much wider apertures. 61
1 he following pifton, deferihed and recommended Confider-
by Belidor, feems asperfedl in thefe refpedls as the na- ll,ly remo- -
ture of things will allow. We fhall therefore deferibe
it in the author’s own w ords as a model, which may by uclidor.
be adopted with confidence in the greateft works.
“ i he body of the pifton is a truncated metal cone y>iate
CCXX (fig. 25.), having a fmall fillet at the gieater ccccxxvu
end. Fig. 26 fhows the profile, and fig. 27. the plan
of its upper bale ; where appears a crofs bar DD, pier¬
ced with an oblong mortife E for receiving the tail of
the pifton-rod. A band of thick and uniform leather
A A (t g. 26. and 28.) is put round this cone, and fe-
cured by a brafs hoop BB firmly driven on its fmaller
end, where it is pvevioufly made thinner to give room
for the hoop.
“ This pifton is covered with a leather valve, fortified
with metal plates GG (fig. 29.) Thefe plates are
wider than the hole of the pifton, fo as to reft on its
rim. There are fimilar plates below the leather of a
fmaller fize, that they may go into the hollow of the
pifton ; and the leather is firmly held between the metal
plates by ferew’s FI, FI, which go through all. This
is reprefented by the dotted circle IK. 1 bus the pref-
fure of the incumbent column of water is fuppocted by
the plates GG, wluffe circular edges reft on the brim
of the w'ater-way, and thus ftraight edges reft on the
crofs bar DD of fig. 26. and 27. This valve is laid
on the top of the conical box in fuch a manner that ita
middle FF refts on the crofs bar. To bind all together,
the