Chapter II: Part 2

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These pipes are simple in design and run direct to the boiler for live steam and convey the exhaust to the atmosphere or condenser as desired. On a recent test at a fair rate of speed the capacity of this pump was shown to be equivalent to taking care of a triple expansion engine of 2,000 I. H. P. On a further test this same pump on a basis of 20 lbs. weight of steam per I. H. P. per hour demonstrated its ability to take care of 3,000 I. H. P. triple expansion engine.

The advantages claimed for this pump are briefly as follows:

Unusual light weight and compactness.

There being NO SUCTION VALVES, working-beams, rock shaft and bearings, beam-links, etc., this pump is simple.

It is economical in the use of steam, by reason of compounding the steam cylinders; also clearance loss is reduced to a minimum by the perfect regulation that is secured by the valve gear described. Full stroke at any and all speeds can be readily maintained.

As the air pistons travel within a distance of less than 1/8 inch of the air cylinder heads, a high efficiency results. Although double-acting, the flow of water and vapors is always in one continuous direction—the same as in a single-acting air pump. Either side of pump can run independent of the other, which means a spare pump to be used in case of accident to the other side of this pump.

Referring to the accompanying table of tests, page 41, it may be claimed that with an average of 36 double strokes per minute this pump handled at the rate of upwards of 26,000 pounds of feed-water per hour, which on a basis of 20 lbs. engine economy shows this vacuum pump capable of taking care of a 1,300 I. H. P. engine at this very moderate speed. By comparing the power required to drive this pump (which aggregated 1.18 I. H. P.) to the I. H. P. of an engine of the power here represented it is apparent that this pump did its work on less than one-eleventh of one per cent. of the I. H. P. of said engine, which is a very excellent showing.

Table No. 4 also shows a very excellent vacuum maintained under extreme duty.

TABLE.

==========================+=========+==========+=========+========
NUMBER OF TEST. | No. 1. | No. 2. | No. 3. | No. 4.
--------------------------+---------+----------+---------+--------
Steam pressure—high | 70 | 120 | 125 |
steam cylinder | lbs. | lbs. | lbs. | --
| | | |
Steam pressure—low steam | | | |
cylinder | 20 lbs. | 40 lbs. | 45 lbs. | 50 lbs.
| | | |
Vacuum in condenser |27-1/2in.| 27in. |26-1/4in.| 25in.
| | | |
Double strokes per minute | | | |
—high side | 37 | 61 | 82 | --
| | | |
Double strokes per minute | | | |
—low side | 35 | 60 | 82 | 88
| | | |
Temperature of hot well— | 106 | 105 | 108 | 112
Fahrenheit | deg. | deg. | deg. | deg.
| | | |
Water pumped per hour— | 13,500 | 22,700 | 30,000 |
high side | lbs. | lbs. | lbs. | --
| | | |
Water pumped per hour— |12,700 |22,300 |30,200 |36,000
low side | lbs. | lbs. | lbs. | lbs.
| | | |
Total water per hour | 26,200 | 45,000 | 60,200 | --
| lbs. | lbs. | lbs. |
| | | |
I. H. P. of high steam | | | |
cylinder | 0.60 | -- | -- | --
| | | |
I. H. P. of low steam | | | |
cylinder | 0.58 | -- | -- | --
Total I. H. P. | 1.18 | -- | -- | --
--------------------------+---------+----------+---------+------

_The Deane Vacuum Pump._ There are a number of novel features exhibited in the construction of this pump; the cylinder has four ports, that is to say _two steam or admission ports and two compression or cushioning ports_.

Referring to the engraving, page 42, Fig. 6, shows the main valve to be a plain ^D^ slide,—directly under it the same valve is shown in section. The projection on the back of this valve fits into the valve piston. The secondary valve, 5, surrounds the main valve and contains two plain slide valves, one on each side. Referring to 3, it will be noted that one of these valves admits steam while the other allows the steam to escape after having done its work of moving the valve piston.

A longitudinal section of this secondary valve and steam cylinder are shown, in 2.

In the engraving, 1, it is shown that the cylinder for each end of the valve piston is jacketed with live steam so that the cylinder itself heats up as quickly as the valve piston, hence the piston cannot stick in the cylinder due to unequal expansion of valve and seat.

The supplemental valve ports are shown in section 4.

_To set the valve of this pump_: Remove the steam chest, place the piston at mid stroke with the lever, plumb, then set the stem at its mid position with the secondary valve in place. See that the tappets measure equal distances either side of the tappet block.

NOTE.—These small ports are not liable to fill with oil and dirt in
practice, on account of their direct connections. If through leakage
or any other reason the valve piston should fail to throw the main
slide valve, the projection B (see 1) on the valve stem (of which it
is a part) compels the valves to move mechanically. So when steam is
turned on, this pump is certain to begin its work.

The water end of this pump consists of a cylinder with valve chambers as shown. The piston rod has two stuffing-boxes, which makes a water seal around the rod so that no air can enter the cylinder, as the chamber between the two stuffing-boxes is kept constantly filled with water. It will be noticed that the suction pipe enters the pump in such a position in relation to the valves that both suction and discharge valves are perpetually immersed in water.

When this pump is pumping air only, there is sufficient water left within the valve chambers to provide a water seal under all working conditions. The valves in this pump are easily reached for inspection or repairs, a hand-hole being provided for each valve, with proper covers, which are easily and quickly replaced.

_The Worthington Vertical Beam Vacuum Pump_ with condenser attached is shown in Fig. 351.

This is a pump of great simplicity and strength. The figure shows _a compound engine_ for using high pressure steam; these machines can be built with simple steam cylinders of equal diameters, but they are not recommended except in special cases; for example where the steam pressure is very low. Each side of the pump end is single-acting, the buckets being of the form used for years in detached air pumps in marine service. The two sides are connected together by a beam and links attached to the cross-heads. As one side comes down and does little work, the other side makes an up-stroke and does full duty in emptying the condenser to which the suction is attached.

The condensing chamber is usually placed at the rear and connects directly with the channel plate at the bottom of the pump. The opening shown in front is for the discharge water.

The steam cylinders are so arranged that either piston may be examined by removing its cylinder head, without disturbing the other cylinders. The valves are of the Corliss, or semi-rotative, type and the high-pressure cylinders are provided with cut-off valves to assure the desired ratio of expansion.

The interior of each air cylinder may be inspected by removing the plates shown in front, near the middle. There are also two plates at the top for inspection of the discharge valves. The four machinery steel columns form a light but very strong frame allowing free access to the working parts.

The next four cuts show Dean Brothers’ twin cylinder air pumps with their special steam valve gear. They are made for and supplied with either surface or jet condensers. See Fig. 352.

The arrangement of the valve gear is such that steam will be applied at the upper end of one piston at the same instant that it begins to act on the lower end of the other. By this device steam is so controlled in the steam chests that no pressure comes on the main pistons, until the moment that both are ready to move, after having reached the full limit of their stroke, thereby securing an exactly uniform, but opposite, motion of the pistons. Fig. 354 is a sectional elevation of the steam cylinder and steam chest; Fig. 353, a front elevation; Fig. 355, a section of the air cylinder, and Fig. 352, an exterior perspective view of the pump.

Each steam cylinder has its own steam piston, piston rod, valve movement, steam chest, etc. A sleeve, _a_, is rigidly attached to each piston rod, and connected to this sleeve is a lever, _b_, the outer end of which connects with a link, _c_, which in turn is connected to a sleeve, _d_, loosely mounted upon the valve rod between collars, _e_. The valve rod, _f_, operates the auxiliary slide valve and admits the steam from above and below the auxiliary piston. This piston has attached thereto the main slide valve, which admits and exhausts steam alternately from above and below the main steam pistons. Any movement of the main piston communicates movement in the opposite direction to the sleeve, _d_, which moves the valve rod only when it strikes one or the other of the collars. As there is considerable lost motion between the sleeve and the collars, the main steam piston will be nearing the end of its stroke when the valve rod begins to move.

Extending through the ends of the steam chests are short piston rods, _g_, which are connected to a centrally pivoted vibrating lever, _h_, mounted on a pivot. When the main steam piston has moved from the top to the bottom of the steam cylinder, the corresponding valve rod has moved in the opposite direction and the auxiliary slide valve has moved upward, opening the port, _i_, to steam and the port, _k_, to the exhaust port. At the moment the main steam piston has completed its downward stroke the auxiliary piston is forced upward and carries with it the main slide valve, _l_. This opens the main steam port and exhaust port, which reverses the movement of the main piston. When the main piston reaches the upward limit of its stroke the auxiliary valve has moved downward, opening the port, _k_, to steam and the port, _i_, to the exhaust, causing the auxiliary piston to move downward, thus reversing the movement of the main valve and piston.

By this arrangement the valve operating piston, _m_, is held at all times immovably at one end of the stroke, except when the main piston is nearing the end of its stroke and is ready to reverse. Supposing the left-hand main piston has not quite reached the upper limit of the stroke, the steam would still be on the lower side of its auxiliary or main valve operating piston and the exhaust open to the other side. We now have steam on the bottom side of both auxiliary pistons, and as they are of equal diameters and are connected by the lever, _h_, they are balanced and cannot move the main steam valves. The right-hand main steam piston must wait until the left-hand piston has completed its stroke before it can reverse, and consequently the movement of the main pistons will always be in opposite directions, and neither can reverse until both have completed their stroke.

There are three ways that this apparatus may be operated: First, the pumps may be operated in conjunction with each other, as is hereinbefore described. Second, the lever, _h_, may be detached from the auxiliary or main valve operating pistons, and the two pumps may then run independently of each other or in the ordinary and well-known manner, each performing its own independent work. Third, by further detaching the link, _c_, on one of the valve gears the auxiliary slide valve, _n_, will remain at rest and the corresponding pump will not move while the other pump continues to operate. These are important features, because, as in case of accident, it may be necessary to use one pump while the other is disabled, and in some cases it may be desirable to operate the pumps independently. The engineer will appreciate this feature, as the stoppage of an air pump is a serious matter.

The piston rods are separable at the crossheads. The crossheads are of steel. The steam cylinders and pump cylinders are connected by six heavy steel stretcher rods. Adjusting valves are fitted to steam cylinders for controlling motion of pistons. The valve gear is provided with a special lever adjustment by which the length of stroke of pistons may at any time be changed, even while the pump is running.

In Fig. 356 is shown a form of independent vacuum pump, with its condenser, built by the Conover Mfg. Co.

This apparatus consists of a jet condenser with air pump, boiler feed pump, and engine to drive both, combined as one machine. The air pump is a single acting bucket plunger pump, driven by a crank shaft, turned by the engine, which is a single cylinder compound automatic cut-off engine, and also drives the boiler feed pump; it is of the trunk pattern, and the small space around the trunk on the top side of the piston forms the high pressure cylinder. Steam is admitted to the high pressure side, at boiler pressure, and is cut off and expanded and exhausted into the receiver, whence it is admitted under the bottom side of the piston, where it is again cut off and expanded, finally exhausting into the condenser.

_The piston makes the down stroke when the air pump makes the up stroke_; and it will be seen by referring to the cut that the engine does nearly all its work when making the downward stroke. When steam is acting on the top side of piston at high pressure, the vacuum at the same time is pulling on the full area of the piston underneath.

When the engine makes the up stroke, the steam at low pressure from the receiver acts to push the piston up; and as the air pump is doing no work then, being on its down stroke, the only work of the engine is to keep the machine up to speed.

It will thus be seen that the engine is suited to meet the demand of the large power on one stroke, and very little on the other, thus adapting itself admirably to its requirements.

The valves are of the Corliss type, and do not trip; the cut-off being set by hand, does not require to be changed or altered, as the speed is controlled by a throttling governor.

Fig. 357 shows a cross section through the steam cylinder of this vacuum pump.

_The Edwards air and vacuum pump_ is shown in Figs. 358, 359 and 360, in which it may be perceived that both foot and bucket valves are dispensed with; the only valves used are those which in other pumps are known as head or discharge valves.

The following brief description of its leading features will be understood by reference to the illustrations: Fig. 358 is a sectional view through the center of the air pump, but the piston and rod are shown as a full view.

The action of this pump is as follows: the condensed steam flows continuously by gravity from the condenser into the base of the pump, and is there dealt with mechanically by the conical bucket working in connection with a base of similar shape. Upon the descent of the bucket the water is projected silently and without shock at a high velocity through the ports into the working barrel (see Fig. 359). The rising water is followed by the rising bucket, which closes the ports, and, sweeping the air and water before it, discharges them through the valve at the top of the barrel.

It may be said that however slowly an ordinary air pump with foot and bucket valves may be running, the pressure in the condenser has to be sufficiently above that in the pump to lift the foot valves, overcome the inertia of the water, and drive the water up through the valves into the barrel where the water is dealt with mechanically. The higher the speed of the older type of pump the greater is the pressure required to overcome these resistances owing to the very short space of time available, and as any increase of pressure in the condenser is accompanied by a corresponding increase of back pressure in the low pressure cylinder, hence the absence of the valves referred to allows a higher speed of the plunger. The elimination of the foot valves it is claimed gives from 1/2 to 1 inch better vacuum.

Another advantage claimed for this pump is that clear air inlets are maintained—see Figs. 359 and 360. Under ordinary working conditions, when the bucket descends and the ports open, there is no obstruction between the condenser and the pump; the air has a free entrance while immediately afterward the water is injected into the barrel at a high velocity. Thus, instead of obstructing the entrance of the air, the water tends to compress that already in the barrel, and to entrain or carry in more air with it.

The bucket or piston is a hollow casting with water grooves instead of packing rings.

The valve seat is constructed with a rib between each valve and a lip around the outer edge, so that each valve stands in its own water and is separated from the others. This forms a ready means of testing the relative tightness of each valve.

The cast iron working barrel is lined with brass.

The pump rod is Tobin bronze, and valve plate and valves of composition. These pumps are either single, twin, triplex, and are steam, electric or belt driven, for stationary, marine or sugar plantation service.

The steam driven pumps are built with either single or compound steam cylinders, fitted with new and improved valve gear, and with their arrangement of fly-wheels, insures smooth running, making full strokes free from vibration.

AIR COMPRESSORS.

_Compressed air_ is air compressed by mechanical force into a state of more or less increased density. _The power obtained from the expansion_ of greatly compressed air in a cylinder, on being set free is used in many applications as a substitute for steam or other force as in operating drills, shop tools and _engines_ which are driven by the elastic force of compressed air.

_A compressor_ is a machine usually driven by steam by which air is compressed in a receiver so that its expansion may be utilized as a source of power at distances where an ordinary engine could not be conveniently used.

The compressor proper comprises two sets of valves, usually designed to be opened automatically by excess of pressure under them and to be closed by gravity or by the action of springs when the pressures become equal. The inlet valves open just after the piston commences its stroke, when the expansion of the compressed air remaining in the cylinder behind the piston has lowered the pressure above the valves. They close at the end of the intake stroke, just as the piston comes to rest. The outlet valve lifts during the compression stroke, at about the time the rising pressure in the cylinder becomes equal to that in the outlet passage above the valves; and they close when the flow of air ceases as the piston completes its stroke.

Any of the accurately fitted steam engine valve gears may be used for compressors, observing only that the compressor is in every way a reversed steam engine.

Compressed air is already used in the operation of

1. Cranes, hoists and motors of all types and of all capacities.

2. Portable drilling, reaming and tapping machines.

3. Riveters and stay-bolt cutters, calking and chipping tools.

4. Shop tools of all kinds.

5. Air brakes.

6. Sand blasts.

7. Rock drills and coal mining machines.

8. Pneumatic locomotives and street cars.

and also for the following diversified uses,

1. Pumping water, sewage, oil and acids.

2. Raising sunken vessels.

3. Refrigerating and ice making.

4. Transmitting messages through pneumatic tubes.

5. Cleaning carpets and railroad cars and seats.

6. Sinking caissons and driving tunnels through silt and soft earth.

7. Tapping iron furnaces.

8. Transmitting power for all purposes.

_The office of the air compressor is to store up air under high pressures_, which can be utilized at a greater or less distance, without sustaining any loss by condensation in the pipes, as is the case of carrying steam in pipes long distances.

Air stored under pressure in a reservoir can be used expansively, in an ordinary steam engine returning an equivalent amount of work that was required to compress it—less the friction.

The admission of the air being through a single tube, it creates a constant flow of air in one direction only, thus filling the cylinder at each stroke with air at atmospheric pressure. This movement gives a momentum to the air which causes it to fill the cylinder to its fullest extent at each stroke.

_Air compressors may be driven in various ways_, but the most commonly used are those which are directly connected to a steam engine, thus doing away with intermediate machinery. When the air piston draws in a charge of air, the air fills the cylinder at atmospheric pressure, or a little below, and on the return stroke of the piston it has to be compressed to the same pressure as in the receiver before it can lift the delivery valve, and as the valve is held to its seat by a spring, and also by its own weight, the pressure has to be considerably above that of the receiver before the valve will lift. To overcome this the valves are operated by mechanical means, which lifts them at a point of the stroke, when the pressure in the cylinder corresponds with that of the receiver.

This arrangement avoids pounding of the valves as well as the noise caused by the air when rushing at much higher pressure from the cylinder into the receiver.

For the sake of economy, air compressors are compounded, as for example, by drawing the air into a large cylinder and compressing it to a certain stage, whence it passes into a smaller cylinder, which compresses it to a much higher pressure.

In a simple compressor, for very high pressures, there is at the end of the stroke a large volume of air left in the clearance space, which expands on the return stroke, to atmospheric pressure, before another charge of air can be drawn in.

But in the compound compressor, the air is delivered from the low pressure receiver to the high pressure cylinder far above atmospheric pressure, thus the remaining air need not expand so much and allows the cylinder to take a larger volume of air. The load is also distributed more evenly.

The following are valuable “points” relating to the care and management of air compressors.

As in a steam pipe line, elbows should be avoided in an air pipe line but unlike a steam pipe it should be larger.

A mistake is sometimes made in purchasing a compressor built for a low altitude and trying to run it in a higher elevation; the machine then experiences the same trouble that some people do, in not being able to get breath enough under the changed conditions.

The use of cheap oils, especially in an air cylinder is a most serious mistake, as the least tendency to gum will prevent the valves from properly seating, and even with the best of oils, it is well to use a small amount of mineral oil at times.

In localities where the water is bad, the water jacket will require extra attention, as it gets as badly scaled like steam boilers, principally due to a very slow or retarded circulation, which allows the sediment to settle, and should the water supply be shut off, even for a few minutes, the cylinder heat will bake it so hard as to give considerable trouble. It is a good plan to put a good boiler compound in the water jacket, and run the machine for some time without any circulation.

In this case good judgment must be used not to run too long or too fast, as the cylinder will heat very quickly and is liable to be damaged.

There are many emergency ways of stopping small pipe leaks; any good sticky substance, such as tar, wax, tallow candles, or even chewing gum, melted and applied on narrow strips of cloth and wound as a bandage, will be found handy.

It should be remembered that leaks in an air pipe line are as bad as in a steam pipe line, and should receive as much care.

_The theoretical operation of air compressors may be thus explained_:

If a tight cylindrical vessel, containing one cubic foot of air at atmospheric pressure, be fitted with a piston which is free to move up and down but yet perfectly tight, the air in the vessel will have no means of escape, and the pressure within and without the vessel, both being atmospheric, are balanced.

Now, if the piston should be loaded with a weight, the pressure on the outside would be that due to the atmosphere, plus the weight, while the pressure from the inside is simply equal to atmospheric pressure; thus the piston is forced to descend, but as the air inside of the cylinder has no means of escape, the volume it fills being diminished, its pressure rises until the pressure under the piston balances that above it.

If, for example, the area of the piston should be 100 square inches, and the weight with which it is loaded be 100 pounds, assuming the piston to be without weight, the pressure below will have to react with an equal force to hold the piston stationary, which in this case would be 1 pound to the square inch above atmospheric pressure, and the piston would have to descend sufficiently to cause this increase of pressure, which descent would be equal to 1/16 of the total fall of the piston. By adding another 100 pounds above, the pressure would rise to 2 pounds to the square inch. The cylinder is thus charged with compressed air.

_Liquid Air_ is a marvelous result of compression. It liquefies at a
pressure of 573 pounds per square inch, at the reduced temperature
of -220° F.; at atmospheric pressure it boils at-312° F., at which
temperature it can be handled like water. _Air_ is the vapor of a
liquid, and acts in its properties like the vapor of other liquids.
Liquid air in color is like that of a blue sky on a cloudless day.

“_Denys Papin_ was the first to propose and make, in 1653, an actual
trial of the transmission of power to a distance by compressed
air. It was the fertile and mechanical brain of Papin that first
conceived the idea of the pneumatic tube for transmitting parcels
by air pressure.” Historical Note by Hiscox.

If now the bottom of the cylinder should be connected by means of a pipe to another vessel of larger capacity called a receiver, the pipe having been closed by a valve in it during compression, and the valve should be opened, the piston would at once commence a further descent, the compressed air escaping into the receiver, until the pressure in the receiver and cylinder is equalized, or the piston reaches the bottom of the cylinder, which it will do, if the receiver is large enough. Then the valve closes, stopping communication between cylinder and receiver, and the piston is drawn upward; at the same time air is again admitted to the cylinder by another valve, which closes when the piston reaches the top, and the same operation is again repeated.

The receiver can thus be charged with compressed air and by loading the piston very heavy the pressure can be raised quite high.

Now, if the piston, instead of being loaded by weights, be connected to the piston rod of a steam engine, or by means of a connecting rod to a crank (which is rotated by a belt or some other driving mechanism, and the valves be operated automatically, as the valves on a water pump), the simple apparatus is converted into a perfect air compressor, _which really is nothing else than an air pump_, and the air can be pumped into the receiver against a high pressure the same as water is forced into an elevated reservoir by a pump.

As air is a compressible gas, it acts a little different in the air cylinder from the almost incompressible water in a pump.

To lift the valves of an air compressor by the compressed air pressure in the cylinder (added to the pressure of their springs besides the receiver pressure), the air would have to be compressed considerably above the receiver pressure before it would lift the valve which allows it to flow from the cylinder into the receiver, and then the valve would not open freely as a pump valve, but would chatter, causing a disagreeable noise, and damaging the valve.

_To avoid this, the valves of an air compressor are operated by mechanical means._ Some devices operate the valve directly as soon as the pressure in the cylinder reaches that of the receiver, while others simply release it of the spring pressure, the valve itself being lifted by the air itself. Such devices generally give the valves a full free opening, without noise.

_The blowing engine_ is almost identical with the air compressor. The chief difference between them being the ratio of steam cylinder to air cylinder. While the air compressor furnishes a comparatively small amount of air at very high pressures, _the blowing engine delivers a very large volume at lower pressures_.

Blowing engines are mainly used in large blast furnaces, smelting works and foundries, to furnish the air pressure for cupolas, air furnaces and smelting ovens.

In Fig. 366 is shown a blowing engine of very large size; the steam cylinder is 42 inches in diameter, the air cylinder 84 inches, and the stroke 60 inches.

_The valve gear is of the Reynolds-Corliss type._ The piston rod is attached to a cross-head extending through the guides, which are formed by the frame, with wrist pins upon each end, from which the two connecting rods are suspended with their lower ends connected to the cranks, as shown in Fig. 366. There are two air piston rods attached to the main piston and held to the cross-head by nuts at points near the guides.

The crank shaft carrying the flywheels, which also form the cranks attached to the ends of this shaft, is located below the steam cylinder. This construction is of the return connecting rod engine design, to economize space.

Both the air and steam valve gears are worked from eccentrics on an auxiliary shaft, driven from the main shaft by bevel gears underneath the steam cylinder.

_The “Imperial” air compressor_ is presented herewith in Figs. 367 and 368.

The “Imperial” compressor is especially designed for use in machine shops, foundries and other industrial establishments where it is not convenient to use a steam driven compressor.

The machine has two vertical, single-acting cylinders, each employing long trunk pistons that act as guides for the lower ends of the connecting rods. By this design, the height of the machine is reduced, stuffing-boxes and crossheads are eliminated, and a minimum number of bearings required. The cranks are set opposite to each other, so that when the piston on one side is ascending, the other side is descending.

The machine is made with duplex cylinders for the low pressures used in sand blast work and the like, and with either duplex or compound cylinders for higher pressures. In the compound type, an intercooler is supplied, through which the air passes from the low pressure to the high pressure cylinder.

_The air cylinders_ are water-jacketed and provided with hooded heads, so that air may be supplied to them from outside the compressor-room; the cylinders are cast in one piece with the frame.

_The air-valves_, both inlet and outlet, are of the poppet type, fitted with light springs, and work vertically. On account of their position at the bottom of the cylinder, they are well lubricated, and, acting vertically, they have little tendency to wear out of line with their seats.

_The air intake passage_ is tapped to receive a supply pipe leading from out-of-doors, or from some place where cool and clean air is obtainable. The compressed air is discharged into a passage which is tapped for a pipe to convey it to the air-receiver.

_All parts of the compressor are easily accessible_ for inspection, adjustment, or repair. The air-heads may be removed without disturbing any of the pipe connections. The valves may be taken out by unscrewing the bonnets.

TABLE

_of parts of the Imperial Compressor_.

_The Norwalk standard compressor_ is shown in Figs. 361 and 362, the latter being a longitudinal section; Fig. 361 is a perspective view; the two compressors are driven by a single steam cylinder having an adjustable cut-off. The air valves are operated by a positive crank motion.

_A view of a Pelton water wheel_ operating a compressor it shown in Fig. 363. The cut represents a compound air compressor in which the valves are operated mechanically. The water which drives the wheel enters through the pipe and nozzle secured in the wheel pit, as represented.

Fig. 364 exhibits a belted duplex air compressor built by Allis-Chalmers & Co.

Fig. 365 shows a vertical duplex compressor driven by a belt.

All the latter, as may be seen by the engravings, have the positive valve motion operated by an eccentric. In selecting an air compressor the following points need consideration: 1, Number of cubic feet of free air required per minute; 2, Altitude, _i.e._, the number of feet above the sea level; 3, Steam pressure and air pressure.

_The use of compressed air for operating mining pumps_, while having advantages in some cases, _is not to be recommended in all_, particularly on account of the low efficiency of the plant as a whole. The loss due to leaks is serious, and the long line of piping with its numerous joints causes much trouble, delay and expense.

_In Fig. 369 is shown a direct acting steam single air compressor_; simplicity in its construction is a leading feature and there are few parts in this pump that are liable to wear.

This apparatus is designed for working pressures up to twenty pounds; it is intended for use in oil refineries, smelting works, blast furnaces and in all situations where compressed air of medium pressure is required. They are variously used for sand blasts, ventilating purposes, and for pneumatic deliveries.

The steam end and valve motion are the regular Deane pattern, assuring positive operation. The air cylinder is provided with a water jacket.

_A power wall or post air compressor_ is shown in Figs. 370-372. The machine is single acting and is recommended where little space is available, as it can be bolted to the wall or to a post, or on the under side of the ceiling. The crank shaft and connecting rod are of cast steel. The bearings are babbitted and adjustable. The piston is of the trunk form, carrying a pin for the connecting rod, and is of extra length to act as a guide for the lower end of the connecting rod. The valves are of the poppet type. These compressors are extensively used in electric power stations for supplying air for removing dust from electric machinery, in bicycle shops for inflating pneumatic tires, maintaining a supply of air in pressure tanks, and for various purposes where a limited supply of air is needed.

These compressors are of _the “Blake” design_ and the following particulars will be of interest.

TABLE.

------------+-----+-------+-------+-------+-------+-------
Diameter | | | | | |
of |2-1/4| 3 | 4 | 5 | 6 | 7
Cylinder. | | | | | |
------------+-----+-------+-------+-------+-------+-------
Stroke. | 6 | 6 | 6 | 6 | 6 | 6
------------+-----+-------+-------+-------+-------+-------
Revolutions | | | | | |
Per | 150 | 150 | 140 | 140 | 130 | 130
Minute. | | | | | |
------------+-----+-------+-------+-------+-------+-------
Piston Speed| | | | | |
in Feet | 150 | 150 | 140 | 140 | 130 | 130
Per Minute. | | | | | |
------------+-----+-------+-------+-------+-------+-------
Cubic Feet | | | | | |
of Free Air | 2 | 3 | 6 | 9 | 12 | 17
Per Minute. | | | | | |
------------+-----+-------+-------+-------+-------+-------
Working | 150 | 150 | 100 | 100 | 100 | 100
Pressure. | | | | | |
------------+-----+-------+-------+-------+-------+-------
Horse | | | | | |
Power | 5/8 | 3/4 | 1-1/2 | 2 | 2-1/2 | 4
Required. | | | | | |
------------+-----+-------+-------+-------+-------+-------
Pipes.
------------+-----+-------+-------+-------+-------+-------
Suction. | 3/4 | 1 | 1-1/2 | 2 | 2 | 2-1/2
------------+-----+-------+-------+-------+-------+-------
Discharge. | 3/4 | 1 | 1-1/2 | 1-1/2 | 1-1/2 | 1-1/2
------------+-----+-------+-------+-------+-------+-------
Dimensions.
------------+-----+-------+-------+-------+-------+-------
Length. | 22″ | 22″ | 24″ | 30″ | 36″ | 36″
------------+-----+-------+-------+-------+-------+-------
Width. | 13″ | 14″ | 15″ | 16″ | 18″ |19-1/2″
------------+-----+-------+-------+-------+-------+-------
Height. | 32″ |33-1/2″| 38″ |40-1/2″| 43″ | 44″
------------+-----+-------+-------+-------+-------+-------

------------+-----+-------+-------+-------+-------+-------
Diameter | | | | | |
of |2-1/4| 3 | 4 | 5 | 6 | 7
Cylinder. | | | | | |
------------+-----+-------+-------+-------+-------+-------
Stroke. | 6 | 6 | 6 | 6 | 6 | 6
------------+-----+-------+-------+-------+-------+-------
Revolutions | | | | | |
Per | 150 | 150 | 140 | 140 | 130 | 130
Minute. | | | | | |
------------+-----+-------+-------+-------+-------+-------
Piston Speed| | | | | |
in Feet | 150 | 150 | 140 | 140 | 130 | 130
Per Minute. | | | | | |
------------+-----+-------+-------+-------+-------+-------
Cubic Feet | | | | | |
of Free Air | 2 | 3 | 6 | 9 | 12 | 17
Per Minute. | | | | | |
------------+-----+-------+-------+-------+-------+-------
Working | 100 | 100 | 90 | 85 | 60 | 60
Pressure. | | | | | |
------------+-----+-------+-------+-------+-------+-------
Horse | | | | | |
Power | 1/2 | 5/8 | 1-1/4 | 1-3/4 | 2 | 2-1/2
Required. | | | | | |
------------+-----+-------+-------+-------+-------+-------
Pipes.
------------+-----+-------+-------+-------+-------+-------
Suction. | 3/4 | 1 | 1-1/2 | 2 | 2 | 2-1/2
------------+-----+-------+-------+-------+-------+-------
Discharge. | 3/4 | 1 | 1-1/2 | 1-1/2 | 1-1/2 | 1-1/2
------------+-----+-------+-------+-------+-------+-------
Dimensions.
------------+-----+-------+-------+-------+-------+-------
Length. | 16″ | 16″ | 16″ | 24″ | 24″ | 30″
------------+-----+-------+-------+-------+-------+-------
Width. | 13″ | 14″ | 14″ | 14″ | 14″ | 18″
------------+-----+-------+-------+-------+-------+-------
Height. | 28″ |29-1/2″|33-1/2″|37-1/2″|37-1/2″| 42″
------------+-----+-------+-------+-------+-------+-------

_With increase in altitude_ the barometric or atmospheric pressure falls from 14.7 pounds per square inch at sea level to about 10 pounds at 10,000 feet above sea level. Since the density of the air decreases with its pressure it is obvious that at such an altitude the total weight of air handled by a given displacement is considerably less than at sea level; and that to fill any volume—a rock drill cylinder, for instance—with air compressed to 90 pounds, a greater free-air displacement will be necessary than would be required at sea level. The relative capacities of a given displacement to do work—as through rock drills or pumps—at varying altitudes are figured in the following table:

CAPACITIES AT VARYING HEIGHTS ABOVE SEA LEVEL.

==========+=========+==========
Feet above|Barometer| Relative
Sea Level | Inches |Capacities
----------+---------+----------
0 | 30.00 | 1.000
500 | 29.42 | .983
1000 | 28.87 | .967
1500 | 28.33 | .954
2000 | 27.79 | .938
2500 | 27.27 | .924
3000 | 26.76 | .909
3500 | 26.25 | .894
4000 | 25.75 | .879
4500 | 25.26 | .867
5000 | 24.78 | .856
6000 | 23.85 | .827
7000 | 22.95 | .800
8000 | 22.10 | .772
9000 | 21.22 | .750
10000 | 20.43 | .725
12000 | 18.92 | .677
----------+---------+----------

The fact that the heating effect of compressing air from an initial pressure of 10 pounds absolute to 90 pounds gauge pressure is theoretically equivalent to that of compression to 132 pounds at sea level, _makes a two-stage arrangement more imperative in high level work than under ordinary conditions_.

COMPOUNDING OR TWO-STAGE COMPRESSION.

The two-stage or multi-stage system of air compression is used generally for high pressure work. The system is most usefully employed between 40 and 120 pounds gauge pressure. For the moderate working pressure of 90 to 100 lbs., the two-stage compression has demonstrated its efficiency chiefly for the reason, that the heat generated in the last half of the stroke of a single compressor is by the two-stage process greatly reduced.

Further compounding, for pressures above 100 pounds, becomes quite necessary to secure the advantages named hereafter; the two-stage has proved advantageous up to 500 lbs., three-stage up to 1,000 lbs., and four-stage compression up to 3,000 lbs.

As the pressures increase, however, the machines become more and more complicated, owing not only to the greater power required, but also to the heating of the air during compression. The use of water-jackets for cooling the air in the compression cylinders is general, but this does not effect thorough cooling, as only a small portion of the air in the cylinder comes in contact with the jacketed parts. This difficulty has led to the use of compound machines, in which case inter-coolers are generally used between the different stages of compression, which cause the air to shrink in volume between the stages.

Briefly summed up, the chief advantages of multi-stage over single-stage compression are:

1. _Lower average temperature_, resulting in lower average pressure, and permitting the compression of the same volume of air with less expenditure of energy.

2. _Increased safety and ease of lubrication._ When high final temperatures prevail, part of the lubricating oil vaporizes, and wear on the piston and cylinder becomes rapid. Under exceptional circumstances the combination of air and oil vapor may reach the proportions of an explosive mixture, and if the compression temperature passes its flash point damage may result. Such accidents are, however, very rare even in single-stage work; in multi-stage compression, with proper intercooling, they are impossible.

3. _Greater effective capacity in free air._ The final pressure in the low pressure cylinder is much lower than in a single-stage machine, and the air confined in the clearance spaces when expanded down to atmospheric pressure occupies comparatively little space. Consequently the inflow of air through the suction valves begins at an earlier point in the stroke.

4. _The air delivered by a two-stage or multi-stage compressor is dryer than that furnished by a single cylinder._ Under constant pressure the power of air to hold watery vapor decreases with its temperature, and during its passage through the inter-cooler much of the original moisture in the air is precipitated. Consequently less trouble is experienced from condensation in the discharge pipe.

A properly designed inter-cooler should reduce the air in the cylinders to the temperature of the outside air. The economy of compressing in several stages—or, in other words, compound compressors—is shown from the fact that in compressing air up to 100 lbs. the heat loss reaches about 30 per cent. By compressing in two stages, this loss is cut down to less than half; and in four stages, it is reduced to four or five per cent. It is evident, therefore, that the higher the pressure required the more essential is the use of compound machines.

_The inter-cooler_ is the vital feature of the two-stage or multi-stage machine. In this construction the air is partially compressed in one cylinder; it is then passed through an inter-cooler where it is cooled and finally is compressed to the desired degree in the second or other additional cylinders.

An inter-cooler is shown in Fig. 373. The cooling surface consists of a nest of small brass water tubes. These tubes break up the stream of air entering the cooler, while their thin walls insure rapid conduction. The receiver volume formed by the connecting pipes and inter-cooler body results in a nearly uniform discharge pressure in the low-pressure cylinder. The air being outside of the tubes encounters practically no frictional resistance, and its slow passage allows time for cooling. A pocket, with gauge glass attached, is so placed as to catch any precipitated moisture which might otherwise enter the high-pressure cylinder.

_An after-cooler_ is shown in Fig. 374. This serves to reduce the temperature of the air after the final compression.

_The heat of compression_, as may be judged from the foregoing, relating to inter and after-coolers is a feature of interest. The temperature to which it finally attains depends, 1, upon the initial temperature; 2, upon the degree of compression, or in other words, _the amount of work expended_ upon the compression.

The extent of this heating is shown in the following table, _for dry air_ when compression is performed with no cooling.

Temperature of air before compression, 60° 90°
Temperature of air compressed to 15 lbs. 177° 212°
„ „ „ „ 30 lbs. 255° 294°
„ „ „ „ 45 lbs. 317° 362°
„ „ „ „ 60 lbs. 369° 417°
„ „ „ „ 75 lbs. 416° 465°
„ „ „ „ 90 lbs. 455° 507°
„ „ „ „ 105 lbs. 490° 545°
„ „ „ „ 120 lbs. 524° 580°

_The Norwalk compound compressor_ is shown in outline by the cut 375. The large air cylinder on the left determines the capacity of the compressor; for illustration assume its piston at 100 square inches area; the small air cylinder can have an area of thirty-three and one-third square inches.

_The small piston only encounters the heaviest pressure_; at 100 pounds pressure the resistance to its advance is 3,333 pounds. _The resistance against the large piston is its area multiplied by the pressure which is caused by forcing the air from the large cylinder into the smaller cylinder._ In this case it is thirty pounds per square inch. But as this thirty pounds pressure acts on the back of the small piston, and hence assists the machine, the net resistance to forcing the air from the large into the small cylinder _is equal to the difference of the area of the two pistons multiplied by the thirty pounds pressure_. This is sixty-six and two-thirds by thirty, and equals 2,000 pounds.

Hence 2,000 pounds, the resistance to forcing the air from the larger into the smaller cylinder, plus 3,333 pounds, the resistance in the smaller cylinder to compressing it to 100 pounds, is the sum of all the resistances in the compound cylinders at the time of greatest effort. This is 5,333 pounds. By thus reducing the work to be done at the end of the stroke, more work is done in the first part, and the resistance is made nearly uniform for the whole stroke.

NOTE.—Arrows on the water pipes show the direction of the water
circulation. When the pistons move as indicated by the arrow on the
piston rod, steam and air circulate in the direction shown by arrows
in the cylinders.

A—Inlet Conduit for Cold Air.

B—Removable Hoods of Wood.

C—Inlet Valve.

D—Intake Cylinder.

E—Discharge Valve.

F—Inter-cooler.

G—Compressing Cylinder.

H—Discharge Air Pipe.

J—Steam Cylinder.

K—Steam Pipe.

L—Exhaust Steam Pipe.

N—Swivel Connection for Crosshead.

O—Air Relief Valve, to effect easy starting after stopping with all
pressure on pipes.

1—Cold Water pipe to Cooling Jacket.

2 and 3—Water Pipes.

4—Water Overflow or discharge.

5—Stone on end of Foundation.

6—Foundation.

7—Space to get at Underside of Cylinder.

8—Floor Line.

THE AIR LIFT PUMP.

The Air Lift is one of the simplest methods of raising water from underground sources. The main principle of its operation may be stated thus: _air under pressure is conveyed into the lower end of the water pipe through a suitable foot piece_.

City and town water works, asylums and hospitals, plantations, railway water tanks, irrigation, private country houses, pumping mines, ice manufactories, breweries, cold storage and packing houses, textile mills, dye works, bleacheries, sewerage installations, dry docks, seaside water works, stock farms; in fact, everywhere that clear and abundant water is needed are opportunities for the application of the Air Lift System of pumping water.

Nor is it alone for securing public water supplies that the Air Lift is of special value. Within recent years the question of an abundant and pure water supply for manufacturing, irrigation and other uses has become one of equal importance. After an extensive experience, two general systems have been devised for utilizing the water which lies immediately below the surface of the ground. One, known as the Deep-well Pump System, for which a working pump is used, and the other the Air Lift System, which employs compressed air to raise the water, either by means of its inherent expansive force or the difference in specific gravity between compressed air and water.

NOTE.—Dr. Julius J. Pohle is admitted to be the original inventor
of this admirable and useful device. At first all systems by which
water or liquids were lifted by compressed air were more or less
extravagant, but with large experience and with improvements in air
compressor economy, the Air Lift has made valuable strides. Dr. Pohle
was actively associated with the Ingersoll Sargeant Co. until his
death, 1896, since which time his system has been further improved
and developed by a wider application and broader experience.

_Theory of the Air Lift._ Opinions differ as to the true theory of the Air Lift. A common Air Lift case is one where there is a driven well in which the water has risen approximately near the surface. In this well is placed a large pipe for the discharge of the water, which is known as an “_eduction pipe_.”

This pipe does not touch the bottom of the well, but is elevated above it so as to freely admit the water through its lower open end. Alongside of this pipe, either on the outside or within, is a small pipe properly proportioned and intended to convey compressed air to a point near the bottom of the eduction pipe. It is usual to provide a “foot-piece,” see Fig. 378, which forms a nozzle connecting the air pipe with the water pipe, but in what is known as the “central pipe system” this foot-piece is not used, the air pipe being placed within the eduction-pipe to a point near the bottom, where it discharges the compressed air into the water column.

Many neighborhoods are dependent upon well water, and there are few districts where an ample supply is not to be secured from wells properly made; this water is generally pure and wholesome. It is also of uniform temperature the year round—cool and pleasant in the summer, because the underground pipe and earth temperature remain uniformly low. In winter, well water being warmer than that taken from ponds and rivers, is not so apt to freeze, and, from all considerations of temperature and purity, well water is greatly to be preferred. Many cities located on rivers having a gravel bed formation find that, by placing wells of suitable construction far enough back from the bank, there is a natural filter bed, leaving the water clear, even when the river itself is muddy. When river or other surface water is good the wells may be sunk close to the edge, the water flowing down from the top of the wells.

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Pumps and Hydraulics, Part 2 (of 2)Chapter II: Part 2

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