522 
utility, and warrant the recommendation of 
It, as the best adapted for the purpose of any 
pump hitherto invented. _ . . 
The great desideratum in a piston is, that it 
is as tight as possible, and has as . little 
friction as is consistent with this indispen- 
sable quality. 
The common form, when carefully exe- 
cuted, has these properties in an eminent de- 
gree, and accordingly keeps its ground amidst 
all the improvements which ingenious artists 
have made. It consists of a hollow cylindei , 
having a piece oi strong leather fastened 
round it, to make it lit exactly the bore ot tne 
barrel, and a valve or flap to cover the hoie 
Through which the water rises, the greatest 
difficulty in the construction of a piston, is 
to give a passage through it tor the water, 
and yet allow a linn support for the valve and 
fixture for the piston-rod. It occasions a 
considerable expence of the moving power 
to force a piston with a narrow perforation 
through the water lodged in the working- 
barrel. When we are raising water to a 
small height, such as 10 or 20 feet, the power 
so expended amounts to a fourth part of the 
whole, if the water-way in the piston is less 
than one-half of the suction of the barrel, and 
the velocity of the piston two feet per second, 
which is very moderate. I here can be no 
doubt, therefore, that metal pistons are pre- 
ferable, because their greater strength allows 
much wider apertures. F or common pup- 
poses, however, they are made of wood, tis 
elm or beech. 
There are many ingenious contrivances to 
avoid the friction of the piston in the pumps; 
but this is of little importance in great works, 
because the friction which is completely suffi- 
cient to prevent all escape of water in a well- 
constructed pump, is but a very trilling part 
cf the whole force. 
In the great pumps which are used in 
mines, and are worked by a steam-engine, 
it is very usual to make the pistons and valves 
without any leather whatever. The working- 
barrel is bored truly cylindrical, and the 
piston is made of metal, of a size that will 
just pass along it without sticking. When 
this is drawn up with a velocity competent to 
a properly loaded machine, the quantity of 
water which escapes round the piston is insig- 
nificant. The piston is made without lea- 
thers ; not to avoid friction, which is also in- 
significant in such works, but to avoid the 
frequent necessity ot drawing it up tor re- 
pairs through such a length or pipes. 
If a pump absolutely without friction is 
wanted, the following seems preferable, for 
simplicity and performance, to any yve have 
seen, when made use of in piopei situations. 
Let NO (tig. 10), be the surface of the water 
in the pit, and K the place of delivering. 
The pit must be as deep in water as from K 
to NO. A is a wooden trunk, round or 
square, open at both ends, and having • a 
valve, P, at the bottom. Tim top ol this 
- trunk must be in a level with K, and has a 
small cistern, F. It also communicates late- 
rally with a rising-pipe G, furnished with a 
valve opening upwards. L is a beam oi 
timber, so fitted to the trunk, as to till it 
without sticking, and is of at least equal 
leiMh. It hangs by a chain from a working- 
beam, and is loaded on the top with weights 
exceeding that of the column of water which 
it displaces. 
Now, suppose this beam to descend from 
the position in which it is drawn in the fi- 
gure ; the water must rise all round it, in the 
crevice which is between it and the trunk, 
and also in the rising-pipe; because the valve 
P shuts, and O opens; so that when the 
plunger L lias got to the bottom, the water 
will stand at {he level ot K. When the 
plunger is again drawn up to the top by the 
action of the moving power, the water sinks 
again in the trunk, but not in the rising-pipe, 
because it is stopped by the valve O. Ihen 
allowing the plunger to descend again, the 
water must again rise in the trunk to the 
level of K, and it must now flow out at K ; 
and the quantity discharged will be equal to 
the part of the beam below the surface of the 
pit water, deducting the quantity which fills 
the small space between the beam and the 
trunk. This quantity may be reduced al- 
most to nothing ; for if the inside of the trunk, 
and the outside of the beam, are made taper- 
ing, the beam may be let down till they ex- 
actly iit; and as this may be done hi square 
work, a good workman may make it exceed- 
ing accurate. But, in this case, the lower 
half of the beam, and trunk, must not taper ; 
and this part of the trunk must be of suffici- 
ent width round the beam, to allow iree 
passage into the rising-pipe ; or, which is 
better, the rising-pipe must branch off from 
the bottom of the trunk. A discharge may 
be made from the cistern F, so that as little 
water as possible may descend along the 
trunk when the piston is raised. 
The requisites of a valve are, that it is 
tight, and of sufficient strength to resist the 
great pressures to which it is exposed; that 
it affords a free passage to the water ; and that 
it does not allow much to go back whilst it is 
shutting. The clack-valve is of all others the 
most obvious and common. It consists 
merely of a leather flap covering the aper- 
ture, and having a piece of metal on the up- 
per side, both to strengthen and to make it 
heavier, that it may shut of itself. Some- 
times the hinge is of metal. The hinge 
being liable to be worn by such incessant 
motion ; and as it is troublesome, especially 
in deep mines, and under water, to undo 
the joint of the pump, in order to put in a 
nevv valve ; it is frequently annexed to a box 
like a piston, made a little conical on the 
outside, and dropt into a conical seat made 
for it in the pipe, where it sticks fast ; and to 
draw it up again, there is a handle like that 
of a basket, fixed to it, which can be laid hold 
of by a long grappling-iron. The only de- 
fect of this valve is, that by opening very 
wide when pushed up by the stream ot water, 
it allows a good deal to go back during its 
shutting again. 
The butterfly-valve is free from most of 
these inconveniences, and seems to be the 
most perfect of the clack-valves. It consists 
of two semicircular flaps revolving round 
their diameters, which are fixed to a bar 
placed across the opening through the pis- 
ton. Some engineers make their great valves 
of a pyramidal form, consisting of four 
clacks, whose hinges are in the circumference 
of the water-way, and which meet with their 
points in the middle, and are supported by 
four ribs, which rise up from the sides, and 
unite in the middle. This is a most excel- 
lent form, affording a more spacious water- 
way, and shutting very readily. 
the button or tail valve. It consists of a 
plate of metal turned conical on the edge, so 
as exactly to fit the conical cavity of its box. 
A tail projects from the under side, which 
passes through a cross bar in the bottom of 
the box, and has a little knob at the end, to 
hinder the valve from rising too high. Thisf 
valve, when nicely made, is unexceptionable, ; 
It has great strength, and is therefore proper j 
for all severe strains ; and it may be made j 
perfectly tight by grinding. Accordingly, 
it is used in all cases where tightness is of in- j 
dispensable consequence. It is most dur- 
able, and the only kind that will do for pas- 
sages where steam or hot water is to pass 
through. 
The pressure on the pipes in pump-work, 
is. in proportion to the standing height of the ! 
fluid above the part considered ; but the 
weight incumbent on the bucket (or moving 
valve) of a pump in action, is nearly proper- * 
tionable to that of a column of water raised ; 
for though the push of the atmosphere on the 
surface of the spring, when the bucket rises, j 
is really equal to the weight of 33 feet of ] 
water ; yet is this resistance counterbalanced j 
exactly by the weight of the atmosphere, j 
ever incumbent on the surface of the water ? 
thereby raised; so that in fact, all the ad- 
vantage to be obtained by hydraulic ma- : 
-chines, as well indeed as from all other pieces : 
of mechanism whatever, is only the putting 
matters into a convenient method of being 
executed ; and the performance depends on j 
the moving power entirely, under the disad- I 
vantage of friction always against it. 
A pump intended to raise water to any 
height whatever, will always work as easy, 
and require no greater power to give motion , 
to the bucket, if both the valves are placed 
towards tire bottom of the pipe, than it they 
were fixed 33 feet above the surface of the 
water. 
The playing of the piston thus low in the 
pipe will, besides, prevent an inconvenience 
which might happen was it placed above, 
viz. in case of a leak beneath the bucket, 
which, in a great length of pipe, may very 
easily happen, the outward air getting 
through, would hinder the necessary rare- 
faction of the air in the barrel on moving the j 
piston, and consequently the pump might 
fail in its operation. This can only effectu- 
ally be prevented, by placing the puinp-j 
work in or near the water ; in which case, 1 
should any leak happen upward, in will only 
occasion the loss of some of the water, with- i 
ont any other inconvenience ; and the lea- 
ther valves being kept under water, will al- 
ways be found supple, pliant, and in con- 
dition to perform their office. 
Placing the pump-work (that is, the valve 
and piston) pretty low' and near together, 
will also prevent the inconvenience of not 
being able in all cases, to fetch up water from 
the spring by the ordinary pump, when of an 
equal bore, by reason of the shortness of the 
stroke; which therefore cannot rarefy the] 
air sufficiently to bring the water up to the] 
piston from the lower valve. For instance: 
Take a smooth-barrelled pump, 21 feet long, j 
having its piston fetching, suppose a foot 
stroke, placed above, and the clack or fixed! 
valve at the other end below. By the play-! 
uig of' the piston, admit it possible for wat«d 
