« PrejšnjaNaprej »
UMPS, Compressed-Air. During recent power just as a belt or transmission rope, but
years much progress has been made in the air never wears out, may be carried to any the art of pumping water by com- distance and at any angle, has little inherent
pressed air. At first all methods friction and possesses the highest efficiency in of lifting water or other liquids by means transmission. The system eliminates all trouble of compressed air were deemed extrava- from freezing since the air is used repeatedly gant, but the development of various systems and moisture once removed cannot be returned. has been such that water may be pumped with While it requires two pipe lines instead of one, marked economy and rapidity by compressed the pipe cost is frequently less because of the air. The direct-acting piston or plunger pump, smaller pipe size permitted. The pump cylinof simple or duplex type, is operated with little ders may be smaller because of the higher effececonomy with steam as a motive power. One tive pressure per square inch and the losses in hundred and fifty pounds of steam per horse clearance, often enormous, are entirely elimipower per hour is a fair figure to take for this nated. The great economy in this system is machine. Experiments have shown that under secured in the higher compression, since the average conditions hardly 50 per cent of the in- scheme is based upon the well-known fact that dicated horse power of the driving cylinder is the greatest losses in compression are thermoutilized in the pump cylinder, the rest being dynamic, which losses are suffered chiefly at absorbed partly by the engine as machine fric- the lower pressures. For example 13.42 horse tion and particularly by the friction of the water power will compress 100 cubic feet of free air in passage through valves and chambers. per second to 60 pounds pressure, starting at
Compressed air is utilized in pumping in atmospheric pressure. This same energy will two distinct ways, (1) as the motive power in compress 100 cubic feet of air to 350 pounds, power driven pumps; and (2) directly upon when beginning compression at 60 pounds, givthe liquid in displacement pumps.
ing on the return pipe system 290 pounds availPower Driven Pumps. — The advantage of able pressure with 60 pounds back pressure. A the power driven pump over the displacement reheater on the pump will secure additional pump lies in the faot that it permits the ex- economy. Losses through leakage and transpansive use of the compressed air, resulting mission are supplied by a small booster) comin a considerable saving and economy. Power pressor. Where the pressure is above 60 pounds pumps consist essentially of expansive air en- two-stage pumps are employed; where above gines, which may be either directly connected, 300 pounds, three-stage pumps. belted or geared to some form of duplex or Another method of securing high economy triplex piston or plunger pump, or to the sim- is to employ compound or triple expansion ple, compound or turbine types of centrifugal pumps, reheating the air after each expansion. pump in its various forms. Compressed air is This may reduce the air consumption to 72 or supplied to the air engine from some more or less 13 its volume in the simple pump of the same distant air compressor and this air engine, when capacity. In some cases this same result may specially designed for the use of air involving be secured by the use of three pumps in series, considerations of air valves and low clearance, reheaters being used as before after each exoperates with efficiency and economy. Where pansion and the exhaust from one pump being the magnitude of the operation justifies it, the supplied to the next, with a larger air cylinder. use of the "return pipe system with expansive Displacement or Pneumatic Pumps.--The engines will, in connection with reheaters, se- displacement pump is almost the essence of cure the very highest efficiency.
pumping simplicity and, if its first promises had This type of pump consists essentially of been borne out, it would be a most powerful two parts, an air end and a water end. The factor in pumping problems. As it is, within its compressed air operates a piston which trans- recognized field, it has shown a fitness which mits its energy through the piston rod which, qualifies it especially for the work. In brief, in turn, causes the pump piston or plunger to it consists of two chambers or cylinders which reciprocate and thereby pump water. In the are filled and discharged alternately - the liquid "return pipe) or closed circuit system, the in each chamber being directly displaced by same air is used over and over again, the ex- the admission of the required volume of comhaust from the pumps being piped back to the pressed air through a valve operating autocompressor under a limited back pressure. In matically. this case the compressed air is a transmitter of · The fundamental requirement is a complete submergence of three to six feet, or the setting submergence or weight of water on the outof the chambers in a dry pit at a level so much side of the eduction pipe there would naturally lower than the water to be pumped that the be a constant discharge of air and water. This chambers may fill rapidly by gravity. The fill- is known as the Frizell system and where the ing is done at no expense of power and the lifts are moderate, that is, where the water in discharge with a minimum of friction losses. the well reaches a point near the surface, it is Dirt, sand or grit will not interfere with its very likely that the discharge could be effected operation. Such a pump starts and stops auto- by simple aeration. matically and uses air exactly in proportion to Most air-lift propositions are deep-well cases, the amount of water discharged. It will run that is, the water is lifted a distance greater for weeks without attention and requires prac- than 25 feet. Aeration will not suffice to expel tically no repairs. Standard sizes have capaci- such water, so the idea of piston-like layers of ties up to 1,500 gallons per minute.
expanding air alternating with blocks of water The height to which these pumps will lift is developed. The upward urge of the air to water is limited only by the air pressure used, reach the lower degree of pressure in the atand by an arrangement of several pumps and mosphere and thus restore its equilibrium as reservoirs in series or steps almost any height free air carries or impels the blocks of water may be attained with ordinary moderate air ahead of it to the discharge gate where separapressures. In mine work the displacement pump tion takes place, the air escaping into the atis especially useful in handling water accumu- mosphere and the water flowing away in the conlating in sumps, dips, entries, etc. It is also duit provided. The economy of the air-lift syspeculiarly effective in subways and tunnels, in tem is in direct proportion to the capacity of the automatically discharging the seepage or leak- well to form these piston-like layers and the age water which accumulates. It may also reason why they are formed is after the first serve in the basement of factories and ware- discharge there is kept up a constant struggle houses which are subject to occasional inunda- between the air under pressure and the head of tions by floods or high water. Another very water on the outside of the pipe, each one seekimportant economic use is the lifting of sewage ing to enter the lower end of the eduction pipe. from low-level catch-basins into the trunk sewer When the air pressure is greater than that at a higher level. The same apparatus, but in due to the head of water, a certain volume of modified form, is employed for elevating acids compressed air is admitted into the eduction and heavy chemical solutions or for pumping pipe. If a sufficient quantity of air has been marl, paints and other semi-fluids. In this case admitted in proportion to the diameter of pipe, the air valve is so located that it is not affected and if there is a sufficient pressure in this pipe by contact with the liquid or by corrosive fumes to prevent the free discharge of the air, it is arising therefrom. The capacity of the dis- readily seen how this bubble of air spreads itplacement pump is determined by the size of the self across the diameter of the pipe in a pistoncylinders or chambers and the volume of air like condition. The reason why this piston is available. Employing air at ordinary pressure not elongated and continuous is that the free from a common single stage air compressor discharge of the air, aided by the velocity with with a lift not exceeding 250 feet, the efficiency which everything in the eduction pipe is movof the displacement pump is higher than that ing, causes a fall in the air pressure just suffiof the usual reciprocating plunger pump under cient to allow the water head to press the the same conditions of lift and pressure. There water into the open end of the eduction pipe. are three distinct types of these pumps known In other words, as the air pressure is for the as the Latta-Martin, Halsey and Harris or moment slightly lower, the water pressure which return-air.”
was nearly equal to the air pressure, becomes a The Latta-Martin system employs two little greater and the piston-like layer of water tanks, side by side, with a valve arrangement enters the pipe, shutting off the air. This to convey compressed air to a point near the (chunk" of water rises in the eduction pipe with bottom of the eduction pipe. The air pipe is a velocity equal to that of the rising bubble of connected with a compressed-air reservoir on air and as it has plugged off the air nozzle, there the surface, which is in or near the engine is a momentary rest, during which the air has room in which free air is compressed. Before a chance to accumulate greater pressure, and turning on the air the conditions in the well just controlling the admission and discharge show water at the same level on the outside of water and air. In operation the pump is and inside of the eduction pipe. At the first completely submerged and one cylinder fills by operation we must have sufficient air pressure gravity while air is forcing out the water from to lift to the surface the column of water which the other. When this cylinder is empty, the air stands in the eduction pipe. This goes out en is automatically released, escaping into the atmasse, after which the pump assumes a normal mosphere, and the water enters, the compressed condition, the working air pressure being then air meanwhile being applied to empty the other lowered to stand at a point corresponding with cylinder. The discharge water flows continuthe normal conditions in the well. This is de- ously. termined by the volume of water which a well The Halsey system employs either a single will yield in a certain time and the elevation tank or double tanks, as desired, and must be to which the water is discharged. It was first submerged to insure good operation. The tank supposed that in all air-lift cases the water was fills by gravity, and as the water enters it discharged because of the aeration of the water causes a float to rise, which, when near the in the eduction pipe due to the intimate com- top of the tank, drops a valve and permits the mingling of air and water. Bubbles of air influx of compressed air to discharge the water. rising in water column not only have a The flow of water is intermittent with the single tendency to carry particles of water with the tank, but continuous with the double tank. air, but the column is made lighter, and, with a Neither the Latta-Martin nor the Halsey sys
tem uses compressed air expansively, and as a is tripped by an interior float when the chamber result there is considerable energy lost through is full. The same trip opens the air valve and the escape of the compressed air into the at- allows the compressed air to enter, driving the mosphere - as with the high-pressure steam water before it into the discharge-pipe. With engine.
both these systems the air escapes into the atThe (return-air system overcomes the dif- mosphere instead of returning to the compressor. ficulty of not employing air expansively and in Of all systems of pumping the Harris it no floats and no air valves, outside the engine is certainly the most economical and efficient. room, are employed and the same air is used over and over again, thus eliminating the effect of clearance. This system employs two tanks and its operation consists in brief of pumping air out of one tank and forcing it into the other, and in so doing will draw water into the former and force it out of the latter. The content or volume of air in the system is so
PA!!! adjusted that when one tank is empty the other is full, and at that moment the switch will be automatically thrown, reversing the pipe action and thereby reversing the action of the tanks.
Figure i presents a conventional diagram of the displacement type of compressed-air pumps, drawn in this instance to show the action of the Harris or return-air pump. The air is being pumped out of chamber A and into chamber B, the water from which is passing up the discharge-pipe D, under the pressure exerted by the air on the surface of the water in B. When chamber A is full the valves on the airpump reverse automatically and the air is pumped into A and out of B, the valves in the inlet box below the chambers reverse their
FIG. 3. positions and the water is forced out of A into the discharge-pipe, and a new charge of water
Using the air expansively, all the inherent energy of compressed air is used, and no mechanism being submerged, there is no chance for the system to become inoperative due to breakage or a demand for repairs. This system may be employed for pumping mixtures of sand and water, and operates with a marked degree of economy and reliability.
Air-Lift.- Opinions differ as to the theory of the air-lift. A common air-lift is one where we have a driven well in which the water is comparatively near the surface. We place in
this well a pipe for the discharge of the water. А. B
This is known as the "eduction pipe. This pipę does not touch the bottom of the well, but is lifted above it so as to admit freely the water through its lower end. Alongside this pipe, either on the outside or within, is a second but smaller pipe, properly proportioned; as soon as this pressure overcomes that of the water, the conditions are reversed and another
chunk” of compressed air is discharged into for
the pipe, shutting off the water for an instant. This process is continuous and as regular as the movement of a pendulum.
As these "chunks of air approach the sur
fact they are gradually enlarged, because of un ieli
the reduced load upon them, and it is likely
that before they reach the surface there is a 1
general breaking up of the piston-like layer Aug 111 pitit!
Figure 2 illustrates the action of the deepFig. 1.
well Pohlé air-lift, where the pressure of the is sucked from the reservoir into B as the air air has to be relatively high. The pipe F leads content is exhausted by the air-pump. This the air from the compressor to the foot of the diagram explains equally well the action of the eduction pipe E. Where the diameter of the Latta-Martin and the double-tank type of the eduction pipe is properly proportioned to the Halsey pumps — supposing
only that the cham- weight of the column of water to be lifted, the bers of the two last mentioned are submerged compressed air pushes out of the air-pipe in so deeply in the reservoir that they fill natur- little pledgets, one after another, holding their ally by gravity through a valve in the top which piston-like shape across the diameter of the
cduction pipe, and each lifting its little load them through pipes and orifices under (hydrau-
the constant pressure of the atmosphere - 14.7
hopens the valve at the foot of pipe F, up which the water contained in B is then forced. It is readily seen that the air pressure in B, (supposing the chambers to be of the same dimen
UV sions) will be half that in A. If there is in the series a third chamber (C) of the same size and arrangement of pipes and valves, the air
А pressure in C will be one-third of the original
ly pressure pumped into A. The possible lift from B to C will, of course, be just half that from A to B. Upon the final escape of the air at the top of the lift, chamber A fills with
B. water by gravity and the cycle is renewed. A certain substantial amount of water pressure is necessary to smooth working of the air-lift.
р This is commonly secured by deep immersion of the eduction pipe. Where this cannot be secured an auxiliary air chamber is installed from which the air is pumped, the water flowing in to fill the vacuum as in the ordinary suction pump. On reversing the air, pressure is exerted downward on the water in the auxiliary chamber, thus forming, an artificial (head>
Surface of Water sufficient to lift the air-shaft.
The Pohlé system of air-lift is probably the best known. Sand, grit and small stones are no obstacles in the satisfactory operation of this system. As a matter of fact, in many instances the capacities of the wells have been increased by opening up the well more thor- Fig. 1.-Section View of Modern Suction Pump. oughly through thi removal of the sand. Water pumped by this system is purified to
air pressure outside of that area causes fluids some extent more so in the Frizell system
affected by it to flow into the space in which by the aeration. The system is not limited as
the pressure has been diminished. In the force to the quantity of water that can be handled.
pump the force is applied directly by the pump This will depend upon the capacity of the wells
mechanism to the fluid to be moved, regardto furnish the water. The height of the lift is
less of atmospheric pressure. In its simplest limited only by the degree of pressure imparted form, the modern atmospheric or suction pump to the air. Consult Greene, A. M., Jr., Pump
consists of a cylinder (c) connected at the boting Machinery! (New York 1911); Ivens, E.
tom with a pipe (P), the lower end of which is M., Pumping by Compressed Air) (New York
immersed below the surface of the water. In 1914).
the cylinder are placed two valves (uv and lv),
the lower stationary and the upper attached to PUMPS AND PUMPING MACHIN- a piston (f) at the end of a rod (r), which ERY. In the modern acceptation of the term, moves the piston up and down under the motion a pump is a machine for exerting mechanical of a handle (h). A pipe or spout (s), attached action upon fluids. It is commonly employed for to the cylinder near its upper end, receives and raising liquids to a higher level; for propelling discharges the water raised by the working of
PUMPS AND PUMPING MACHINERY
the piston. Both the valves open upward, and transmit the pressure of the piston to all water the action of the entire arrangement, based in a long pipe line for power purposes. The upon the physical fact that two bodies cannot plunger pump is similar in results, but develops occupy the same space at the same time, is as its pressure by the forcible thrusting of the follows: When the downward stroke of the comparatively large mass of the plunger into handle moves the piston upward, the air in the a chamber already filled with water. The water space A is rarefied, having to occupy a greater being incompressible, a volume of it equal to space, and the partial vacuum thus formed re- the bulk of the entering plunger is driven out lieves the pressure of the atmosphere from the lower valve, which being opened upward by the pressure of the air in the space (B) of the pipe, allows a portion of it to pass into the space (A). When the piston descends under the upward stroke of the handle, the air in the space (A) is compressed, the lower valve
D is closed, and when the density of the compressed air becomes greater than that of the atmosphere, the upper valve is forced open and
E the air passes into and out of the space (D). Thus, by the continued up and down movement of the piston, all the air in the space (B) is
W completely exhausted, the water rising in the Suction pipe under the pressure of the atmos
Y phere upon its surface in the well, until it fills the space (B) up to the lower valve. The next upward movement of the piston empties the air
K in the space (A), which is immediately filled
H with water by the opening of the lower valve. The downward motion of the piston relieves the pressure and allows the lower valve to fall into its seat. The water then in the lower part
FIG. 2. of the pump flows through the valve in the
of the chamber into the transmission pipes. piston into the space (D), from which it is
Both piston and plunger pumps are usually discharged through the spout by the next up
designed to act both on the outward and the ward movement of the piston which at the same
return strokes — the piston sucking in a supply time refills the space (A) by suction. Under
of water behind it as it moves in either directhe laws of fluid pressure discovered by the experiments of Torricelli and others, the height
tion; and the plunger being double-ended, and
working alternately into two chambers divided to which a column of water will rise depends
by a wall or a diaphragm carrying a packing upon the atmospheric pressure at any point on
ring or sleeve. These types are known as the earth's surface, and varies with the altitude of that point. At the level of the sea, the
double-acting pumps. In the sectional diagram
of a piston force-pump shown in Fig. 2, the atmosphere exerts a pressure of 14.7 pounds to
piston P is represented as starting on its outthe square inch, and will support a column of
ward stroke. The water W before it is being water in a closed tube from which the air has
forced upward through valve E into the disbeen exhausted, between 33 and 34 feet in
charge-pipe system D, while valves F and K are height, while upon the top of Mont Blanc, or Pike's Peak, 15,000 or 16,000 feet above the sea, the atmospheric pressure will support a similar column of water only about 16 or 17 feet in height. A knowledge of this fact is important not only in determining the maximum distance at which the lower valve of a pump may be placed from the surface of water to be pumped,
Willia R E but also in every branch of hydraulic engineering in which atmospheric pressure is utilized.
By far the greater amount of pumping done in the economic world is accomplished by
Р force pumps. It is, however, generally the case that the principle of the suction pump is used in combination to a greater or less degree, at
Y mospheric pressure being relied on for pre
PR liminary lifts not to exceed 16 or 18 feet above the basic water level. Force pumps are of two general types: (1)
H K the piston pump, and (2) the plunger pump. In the former a well-fitted piston is driven to and fro in a smoothly-bored cylinder to which the water to be pumped is admitted. The pres
FIG. 3. sure of the moving piston upon the water forces it out of the cylinder by any valve open- held shut by the internal pressure. Valve H in ing freely outward, and thus into pipes through the supply-pipe system opens by «suction, and which it may be raised to heights varying with the supply water flows in behind the advancthe power exerted on the piston; or it may ing piston. On the return or inward stroke,