ROTARY PUMPS.
This class of pumps differs from the centrifugal pump, which is described and illustrated hereafter, in that it includes arevolving piston, while in the centrifugal pump there is a set ofrevolving bladeswhich acts upon the liquid in the same way as a fan acts upon the air;the centrifugal pump receives the water in the center and throws it outward, while the rotary gathers the fluid up and leads it towards a central discharge.
The rotary pump substantially corresponds to the pressure blower, and in many cases is simply the rotary engine reversed; while the centrifugal pump is analogous to the fan-blower. The functions of a rotary are almost identical with those of piston and power plunger pumps.
The rotary pump on account of its cleanlinesshas been quite generally adopted for pumping all heavy liquids, such as starch, paint, soap, gummy oils, beer and hops, sewerage, bleachers, etc.
The rotary pump is used also in places where a piston or steam pump would be objectionable either on account of floor space occupied or for the reason that steam could not be had without too much expense for lifting and forcing water and other liquids which would not nor could not find their way through the tortuous and narrow passages of the average piston and plunger pumps.
For low heads of liquidsthe rotary is also somewhat more efficient than direct acting pumps and the absence of close fitting parts renders it possible to handle water containing a considerable quantity of impurities, such as silt, grain and gravel. This type of pump is compact and is generally self-contained, especially in the smaller sizes, and will deliver more water for a given weight and space occupied than the reciprocating types, while its simplicity of construction not only lessens the liability to derangement, but enables persons having a limited knowledge of machinery to set up and operate these pumps successfully.
Rotary pumps are driven by means of belts from line shafting and by wheel gearing, and also by direct connection to any prime mover such as a steam or gas engine, hydraulic or electric motor.
Rotary pumps may be divided into several classesaccording to the forms of, and methods of working the pistons or impellers, as they are usually called, that is, according to the construction and arrangement of the abutments. The abutment receives the force of the water when driven forward by the pistons or impellers and also prevents the water from being carried around the cylinder, thus compelling it to enter the delivery pipe.In the construction of the impellers or pistons, and of the abutments, lie the principal differences in rotary pumps.In some pumps the abutments are movable, and are arranged to draw back, as shown in Fig.469, to allow the piston to pass. In others the pistons give way when passing fixed abutments, and in others the pistons are fitted with a movable wing, as in Fig.472, which slides radially in and out when passing the abutment.
Fig. 469.
Fig. 469.
Pumps of this type having no packing and springs to prevent leakage and in which the pistons work in cylindrical casings or cylinders are quite durable and in many instances have been known to run for months without stopping. The later construction of this pump is shown in Fig.470; this design of pump is more economical, as a rule, owing to the fact that the strain on the belt is uniform at all points in the revolution of the pistons.
Fig.467, page 194, represents one of the oldest and most efficient forms of the rotary pump. Cog wheels, the teeth of which are fitted to work accurately into each other, are inclosedin an elliptical case. The sides of these wheels turn close to those of the case so that water cannot enter between them. The axle of one of the wheels is continued through one end of the case (which is removed in the figure to show the interior) and the opening made tight by a stuffing-box or collar of leather. A crank is applied at the end to turn it, and as one wheel revolves it necessarily turns the other, the direction of their motions being indicated by the arrows. The water that enters the lower part of the case is swept up by the ends of each cog in rotation; and as it cannot return between the wheels in consequence of the cogs being always in contact there, it must necessarily rise in the ascending or forcing pipe.
Fig.468represents a pump similarly constructed to the foregoing,but having camsshaped so as to reduce the wear.
Fig. 470.
Fig. 470.
In Eve’s pump, shown in Fig.469, a solid or hollow drum,A, revolves in a cylindrical case. On the drum are three projecting pieces, which fit close to the inner periphery of the case. The surface of the drum revolves in contact with that of a smaller cylinder,B, from which a portion is cut off to form a groove or recess sufficiently deep to receive within it each piston as it moves past. The diameter of the small cylinder is just one-third that of the drum. The axles of both are continuedthrough one or both ends of the case, and the openings made tight with stuffing-boxes. On one end of each axle is fixed a toothed wheel of the same diameter as its respective cylinder; and these are so geared into one another, that when the crank attached to the drum-axle is turned (in the direction of the arrow) the groove in the small cylinder receives successively each piston, thus affording room for its passage, and at the same time, by the contact of the edge of the piston with its curved part, preventing water from passing. As the machine is worked, the water that enters the lower part of the pump through the suction-pipe is forced round and compelled to rise in the discharging one, as indicated by the arrows. Other pumps of the same class have a portion of the small cylinder cut off, so that the concave surface of the remainder forms a continuation of the case in front of the recess while the pistons are passing; and then, by a similar movement to that in the figure described, the convex part is brought in contact with the periphery of the drum until the return of the piston.
Note.—In the year 1825, one Mr. J. Eve, an American, took out a patent in England which was practically the beginning of the modern era of rotary engines and pumps. His pump consisted chiefly of a revolving cylinder having three teeth or projections and revolved within a case. A second and smaller cylinder was also placed within this case. The smaller cylinder had one side scooped out to permit each of the teeth upon the large cylinder to pass as they came opposite the small cylinder. The two shafts being geared together the small cylinder was caused to revolve three times to one of the large so that the teeth might pass the small cylinder without interruption.
Note.—In the year 1825, one Mr. J. Eve, an American, took out a patent in England which was practically the beginning of the modern era of rotary engines and pumps. His pump consisted chiefly of a revolving cylinder having three teeth or projections and revolved within a case. A second and smaller cylinder was also placed within this case. The smaller cylinder had one side scooped out to permit each of the teeth upon the large cylinder to pass as they came opposite the small cylinder. The two shafts being geared together the small cylinder was caused to revolve three times to one of the large so that the teeth might pass the small cylinder without interruption.
Figs. 471 and 472.
Figs. 471 and 472.
The next improvement in rotary pumps is shown in Fig.470, page 197. This type was used for many years as a fire pump. The Silsby fire engine of the present day is practically this pump in design although it has packing strips in the center of each of the long teeth of the elliptical gears.
Following Eve’s invention were a series of claims which embodied the design shown in the engraving, see Fig.471, where a sliding partition or abutment, A, was used to imprison the steam. As the piston or inside cylinder turned around, the abutment was pushed up and fell of its own gravity. A strip of metal supported this abutment and furnished a suitable wearing surface upon the surface of a revolving cylinder and also accommodated itself to the tilting motion introduced by the eccentricity of the revolving cylinder.
In Fig.472the sliding abutment has been placed in the side of revolving cylinders and the axis of this cylinder is in its center. In this case the abutment is pushed in by its pressure upon the inside of the case and is thrown out by its centrifugal force assisted by spiral springs.
The engraving, Fig.468, gives a view ofGould’s rotary pump, with the case removed; long practical experience has demonstrated that the revolving cams or pistons are of such a shape as to produce the minimum of friction and wear with the greatest results.
The cases which receive these cams are engine lathe turned and bored and so true and smooth that the cams when in operation create almost a perfect vacuum and will “pick up” water for a long distance and hold it efficiently. The cams are carefully and accurately planed to mesh into each other to fit their case.
It is a point worth noting that if a little good oil be put into the case of these pumps before and after using at first, or simply to pump air with the oil a few times, the cams become as hard upon the surface as tempered steel, and are almost unaffected by long use afterwards. Drip plugs are provided for draining pumps in cold weather. To do this, turn the cams backward a single revolution to release all water.
The Taber pumpis one of the best known of the rotary class. It consists of three parts only, that is to say, (1) the outside shell or case, (2) the piston, and (3) the valves.
Referring to the engravings herewith (Figs.474to481), theoutside case or shell, A, is made either of brass or iron as the case may be, Fig.476, bored out at F to receive the piston, C, Fig.478, to which power is applied at G.
Fig. 474.
Fig. 474.
This cylinder has two heads or covers, BB, Figs.475and477, which close the cylinder and has journal bearings to carry the piston combined with packing boxes to prevent leakage of the liquid passing through the pump. The valves, Figs.479,480and481, DDD, are plates of composition which slip through the piston fitting neatly into the slots, EE, Fig.478.
Figs. 475-477.
Figs. 475-477.
Fig. 478.
Fig. 478.
Figs. 479-481.
Figs. 479-481.
These valves really perform the work of pumping. It will be observed that substances which would easily clog up an ordinary pump with clack valves, will pass through this pumpwithout difficulty; there are no springs in this pump, nor will it get out of order with the average treatment, and it pumps all kinds of liquids, either thick or thin, such as are found between the two extremes of water, andbrewers’ grains.
It is designed to handle a large amount of fluids and semi-fluids under a medium pressure, and being well balanced it may be run fast or slow as desired.
Directions for setting and operating Taber pumps.
1st. Bolt pump firmly to the floor, and if possible set it so that the liquid runs into it, which will add very much to the life and duty of the pump.
2nd. See that all parts are well oiled.
3rd. Experience has proved that common candle wick soaked in tallow is the best material with which to pack rotary pumps. The wick should be double and twisted into a compact rope and driven into the boxes as tightly as possible with a piece of hard wood tapered to fit the box. Such a tool as described is furnished with each pump. Do not under any circumstances use iron calking tools which mar the bearing and causes them to quickly cut out the packing.
4th. If from any cause the pump should become clogged, do not use a lever in starting it. Remove the plug from bottom and work the pulley back and forth till the pump is relieved. If this does not free it, remove the outside head and all parts will be accessible.
Note.—Many of the modern breweries are built with the hop-jack situated upon the upper floors of the brewery, to which the beer and hops mixed are pumped, and the beer allowed to flow directly to the coolers. This pump has been very successfully installed for the past five years, pumping in some breweries 90 feet in height above the pump. The handling of wet brewers’ grains by use of chain conveyors, which are seldom free from infection and which are a continual source of annoyance from breakage, is now overcome by this pump. All styles of these pumps can be washed out clean after use, thereby overcoming entirely the noxious smell so disagreeable to this part of the brewery when conveyors are used. There should be a fall of six to eight feet from the wash-tub into the pump and as nearly perpendicular as possible. Right angle bends in the discharge pipe should also be avoided. By using twenty-four-inch bends wet grains at 70% moisture can be pumped without additional water.
Note.—Many of the modern breweries are built with the hop-jack situated upon the upper floors of the brewery, to which the beer and hops mixed are pumped, and the beer allowed to flow directly to the coolers. This pump has been very successfully installed for the past five years, pumping in some breweries 90 feet in height above the pump. The handling of wet brewers’ grains by use of chain conveyors, which are seldom free from infection and which are a continual source of annoyance from breakage, is now overcome by this pump. All styles of these pumps can be washed out clean after use, thereby overcoming entirely the noxious smell so disagreeable to this part of the brewery when conveyors are used. There should be a fall of six to eight feet from the wash-tub into the pump and as nearly perpendicular as possible. Right angle bends in the discharge pipe should also be avoided. By using twenty-four-inch bends wet grains at 70% moisture can be pumped without additional water.
When putting heads back on the pump use ordinarynewspaper for packing, nothing thicker, as thicker packing destroys the suction.
Prevent all leaks in suction pipe which would impair the vacuum.
The suction should furnish an uninterrupted supply to the pump, to enable the pump to throw its full capacity. Never use pipes smaller than the openings in pump.
Open all drips in cold weather to prevent freezing.
All packing boxes should be kept in order and never allowed to leak.
The illustration, Fig.482, page 204, represents a rotary pump of the Holyoke pattern to be attached by a clutch to a line shaft—the gears, as shown, are merely to transmit the power to the impellers. The safety valve with lever and weight, shown in the cut, are designed to be attached to the discharge pipe to guard against over pressure, which might occur through the closing of valves.
Fig.483shows an emergency pump of the Holyoke rotary pattern. It is of the same general design as the one previously alluded to. It is driven directly from the line shaft by friction gearing instead of toothed wheels. The hand wheel attached to the end of a screw is used to press the smaller friction wheel against the larger and thus transmit the power to drive the pump.
This mechanism is not liable to injury by being thrown instantly into gear in case of fire, as would be the case if gear wheels were used.
These pumps are largely used in mills located in the Eastern United States,as they may be started up in a few moments at full speedwithout slowing down the engine or motor driving the line shaft.
The shaft bearings are all made of large proportions to avoid heating and excessive wear when suddenly put under full load.
Fig. 482.
Fig. 482.
Fig. 483.
Fig. 483.
Figs.484and485are views of arotary pump driven by steamand largely used for fire apparatus. These pumps are in general use in mills and factories, and can be installed wherever the necessary steam and water supply are available.
The pump is built on a rigid iron base plate, and is furnished with air chamber, water-pressure gauge, oil feeders and everything necessary to make it complete and ready for permanent steam and water connections. The discharge outlets can be adapted for forcing water through either pipe or hose.
A perspective view of this pump is given in Fig.484and a sectional plan of the same appliance appears in Fig.485.
Both engine and pump are of the rotary type and the construction of these parts is precisely as described in connection with its adaptation to use in the Silsby steam fire engine.
These pumps can be thoroughly drained and, with their interior surface well coated with oil and No. 2 pure Graphite, they can be “laid up” indefinitely and with certainty as to their starting promptly when wanted in an emergency. Water accumulated in the steam pipe will pass through this cylinder without causing damage, and the free action of the pump will not be defeated by the “sticking” of valves or the corrosion of exposed parts.
In the operation of rotary pumps trouble is often experienced through an improper adjustment ofthe ends of the case. If the case is too long there will be leaks of water pass the ends of the impellers and on the other hand if the case is too short the ends of the impellers will bind and cut, through excessive friction. Hence great care is necessary in adjusting the ends of the case so that the pump may run freely yet without leaks. The packing boxes around the shafts must not be screwed up too tight otherwise the shaft will be injured.
It has been found by costly experience thatfor emergency fire pumps leather belts are unreliable, hence these two pumps, Figs.482and483, are driven by direct connection with the shaft in the first instance and through cast iron friction gearing in the second.
Fig. 484.
Fig. 484.
Fig. 485.—See page205.
Fig. 485.—See page205.
Fig. 486.—See page210.
Fig. 486.—See page210.
The engraving, Fig.487, showsRoot’s rotary pump. This has two impellers which are geared together and each turn at equal speeds towards one another at the top. The engraving, Fig.488, also shows a Root pump withtwo impellers each having three wings or lobes. The pump proper consists of half circles,AA, with air chambers,DD, cast with them, the head plates,B, carrying the bearings, and the revolvers,CC, together with shafts,EE. The shafts carry involute gears at each end which keep the lobes of the two impellers in their relative positions, and rotate them. Either shaft may be made the driving shaft and to deliver water, as shown by the arrows in the cross section, the shafts revolve so that the tops move toward one another.—Same as in the preceding case.
Fig. 487.
Fig. 487.
Fig. 488.
Fig. 488.
The action of this pump is as follows: the suction pipe on starting, being full of air, the first few revolutions of the pump expel the air until the required vacuum is formed, which allows atmospheric pressure to raise water into the pump. It then flows between the case and the lobes into the space,F, and is carried by the impellers to the discharge edge of the case, point,G, where it enters the discharge pipe. Each succeeding lobe brings up an amount of water equal to spaces,FF, thus delivering the contents of the six at each revolution. The irregular form ofthe lobes keeps them in contact at the center line, thus preventing the return of water into the suction below.
Heads of water from 10 to 250 feet are successfully handled by this type of pump, with a slip of from 5 to 15 per cent., according to the discharge pressure.
The three-lobe impellers provide a double lock against the return of water between the case and impellers, at the same time allowing a very free inlet and outlet for the water. The delivery of water from this pump is smooth and continuous.
The large engraving, Fig.486, page 208, shows the exterior of this same pump with journal bearings and gears encased at each end. This pump may be driven by motor or engine.
Large rotary pumps for dredging purposeswith their engine equipment forsalt water service, include surface condenser outfits with air pumps, feed pumps, fire pumps, etc. The dredgesfor fresh waterare very large cross-compound engines, double-acting air pumps and jet condensers with the usual complement of vertical duplex feed pumps, fire pumps, etc. The air pumps are of a very novel arrangement, inasmuch as it is possible by the manipulation of valves and cocks provided for the purpose to separate the pumps and run one side entirely independent of the other side. These dredges are self-propelling and sea-going; some of them are fitted with immense bins in which the dredged material is deposited, and when full, the vessel propels herself out to deep water, dumps the sand or mud and steams back to repeat the operation.
Note.—The operation of these machines is very interesting. A long flexible tube 12 to 15 inches in diameter drops down from the side of the vessel 20 to 30 feet or more to the bottom of the river or harbor upon which the dredging operation is being performed. The upper end of this tube is connected to an immense rotative centrifugal pump revolving at several hundred revolutions per minute and capable of handling many hundreds of tons of water per hour. The lower end of the tube is manipulated from the vessel against the sand bars and mud banks and as the water is sucked upward by the centrifugal pumps a very large proportion of sand and mud goes with it. The centrifugal pumps discharge this water with its suspended material into the tanks on board the vessel or into scows, where the heavy material quickly settles to the bottom, the water flowing back into the sea.The mixture of sand and water which is drawn up the suction pipe is forced a distance of 3,800 feet through a 30-inch pipe to the place where it is to be deposited; the water draining off allows the solid matter to remain.
Note.—The operation of these machines is very interesting. A long flexible tube 12 to 15 inches in diameter drops down from the side of the vessel 20 to 30 feet or more to the bottom of the river or harbor upon which the dredging operation is being performed. The upper end of this tube is connected to an immense rotative centrifugal pump revolving at several hundred revolutions per minute and capable of handling many hundreds of tons of water per hour. The lower end of the tube is manipulated from the vessel against the sand bars and mud banks and as the water is sucked upward by the centrifugal pumps a very large proportion of sand and mud goes with it. The centrifugal pumps discharge this water with its suspended material into the tanks on board the vessel or into scows, where the heavy material quickly settles to the bottom, the water flowing back into the sea.
The mixture of sand and water which is drawn up the suction pipe is forced a distance of 3,800 feet through a 30-inch pipe to the place where it is to be deposited; the water draining off allows the solid matter to remain.