SINGLE AND CROSS COMPOUND DOUBLE ACTING VACUUM PUMPS.

The vacuum pump shown in the engraving, Fig. [346], represents a single cylinder double acting vertical design having but one set of valves and those used exclusively for the discharge.

The suction port is in the middle of the cylinder, A, shown in the sectional view, Fig. [347]. The piston, E, when it passes this port imprisons the water beyond it and pushes this water out of the discharge valves, D D, if the piston is rising, and out of the valves, C C, if the piston is descending. The main discharge pipe is attached to a flange at B.

This pump is made to work easily and steadily by adjusting the cushioning valves, F. F.

The discharge valves are reached through the holes provided for that purpose and covered by plates shown in the engraving, Fig. [347].

The main slide valve moves horizontally for the reason that if it moved up and down the force of gravity would seriously interfere with its regular action.

This slide is moved by a valve piston in the usual way. The parts of the valve may be inspected and adjusted by removing the cover held by the two studs shown.

The outline engraving, Fig. [348], shows a cross-compound double acting vacuum pump, six-inch high pressure, nine-inch low pressure cylinders, by eight-inch stroke, and two air cylinders, ten-inch diameter by eight-inch stroke.

They are piped up to run either high or low pressure, also to run independently by manipulating the cocks, C, and D, as directed in the engraving showing arrangement of valves, Fig. [349], page 41.

Fig. 346.

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.

Fig. 347.

Fig. 348.

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.

Fig. 349.—See page [38].

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 steam cylinder	70 lbs.	120 lbs.	125 lbs.	—
Steam pressure—low steam cylinder	20 lbs.	40 lbs.	45 lbs.	50 lbs.
Vacuum in condenser	27¹⁄₂in.	27in.	26¹⁄₄in.	25in.
Double strokes per minute—high side	37	61	82	—
Double strokes per minute—low side	35	60	82	88
Temperature of hot well—Fahrenheit	106 deg.	105 deg.	108 deg.	112 deg.
Water pumped per hour—high side	13,500 lbs.	22,700 lbs.	30,000 lbs.	—
Water pumped per hour—low side	12,700 lbs.	22,300 lbs.	30,200 lbs.	36,000 lbs.
Total water per hour	26,200 lbs.	45,000 lbs.	60,200 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	—	—	—

Fig. 350.

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.

Fig. 351.

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.

Fig. 352.

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.

Fig. 353.

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.

Fig. 354.

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.

Fig. 355.

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.

Fig. 356.

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.

Fig. 357.

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.

Fig. 358.

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.

Fig. 359.

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.

Fig. 360.

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.

Fig. 361.—See page [70].