Vacuum pump

“ Inspection of the efficiency curves of the various types of vacuum producers, given in Chapter IX, shows that the two-impeller rotary pump has the highest efficiency at this vacuum.
For the operation of systems where carpet cleaning is the most important function and 1-in. hose is found to be the most economical, 14 in. to 15 in. of vacuum at the vacuum producer is necessary, and efficiency curves, given in Chapter IX, show that the piston pump is the best suited for such service. ”

“ The action of the separator is as follows: After starting the motor and turning on a small quantity of water, a vacuum is produced in one tank and through a system of piping to the cleaning implement in use. The dust and dirt collected by the implement is saturated as it approaches the [141] plant and in this saturated condition enters the bottom of a body of water in the tank.
When the accumulating dirt and water reach a certain level a valve is automatically operated which closes the tank’s communication with the vacuum pump and allows its contents to flow off to the sewer by gravity. ”

“ It has met with favor when used with the piston type of vacuum pump without vacuum control, as was the case with the earlier systems. However, when a very high [27] degree of vacuum occurs within the renovator it has a tendency to pull the nap from the pile of the carpet. ”

“ Machines Using Root Blowers as Vacuum Producers. —The use of a Root type of rotary pump as a vacuum producer was first undertaken by the Foster and Glidden Engineering Company, of Buffalo, which marketed the Acme system about 1907, the same company having previously built a similar system for the removal of grain from steam barges. ”

“ We are apt to overlook the fact that a vacuum cleaner depends upon atmospheric pressure to drag the dust and dirt out of a carpet. A vacuum cleaner would not work on the moon, where there is no atmospheric pressure. The apparatus consists of an air pump, usually driven by an electric motor, which exhausts, or partially exhausts, the air from a foot piece that is dragged along the carpet. As the air under atmospheric pressure rushes in through the carpet to take the place of the air that has been pumped out, it carries with it all loose particles of dirt. ”

“ A double-acting vacuum-pump volatilizes the agent in the refrigerator coils, and this is attended with the development of an intense cold, which is communicated to the surrounding mixture, and the latter, by means of a circulating pump, is made to flow through a suitable tank containing vessels of water to be frozen, or, if air-cooling only be desired, through iron tubing placed along the walls or ceiling of the chamber to be cooled. ”

“ A.--The pump frequently works by starts, as if at times it did not draw at all, and then again on a sudden gorged itself with water, so as to throw a great strain upon the working parts. The vacuum, moreover, is by no means so good as it should be, and it is a universal vice of direct acting screw engines that the vacuum is defective. ”

“ Of course, the micro-vacuum pump could be used in vacuum tube manufacture, in a pinch. Vacuum tube companies normally used large-volume pumps instead of the little super-efficient exhaustion pump that could take a few cubic centimeters down to a few millimicrons of mercury.
The electron microscope was a nice hunk of stuff, but the thing was not applicable to anything except research. ”

“ The first pump always remains in motion at its point of highest efficiency. It is evident that this duplex arrangement is more efficient than one large pump when only a very few sweepers are in operation, since, for this condition, the very large pump would have to be run at such a slow speed that the armature resistance would be in circuit, while the single smaller pump would be running at a more efficient speed and with less proportionate motor losses. ”

“ To assist in producing the high vacuum, exhaust passages are made large, the eduction passage E in fig. 2,750 being nearly twenty-three times the area of the steam pipe.
Among other details, a noteworthy feature is a small oil pump K, which circulates oil through bearings of the machinery, the oil being drawn from the tank under the governor shaft and gravitating there after use. No pressure of oil is employed. Stuffing rings prevent leakage; these consist of alternate grooves and collars in shaft and bearing, like the grooves in an indicator piston.
1967 Ques. Why is a high vacuum desirable? ”

“ Though this result can be reached by the use of a static machine as, well as of an ordinary induction coil giving a sufficiently high potential, I have found that by far the most suitable apparatus, and one which secures the quickest action, is a disruptive coil: It is best to proceed in this way: The bulb is first exhausted by means of an ordinary vacuum pump to a rather high degree, though my experiences have shown that this is not absolutely necessary, as I have also found it possible to rarefy, beginning from low pressure. ”

“ If the displacement pump be run at constant speed, every change in the quantity of air exhausted will cause a change in the vacuum produced. This will result in inefficient operation and may result in undue effort being necessary to operate the renovator and in excessive wear on the carpets. ”

“ A modification of the reciprocating pump was manufactured by the Sanitary Devices Manufacturing Company in which [145] light-weight poppet valves placed in the heads of the cylinder were used, as indicated in Fig. 79. Curves of the watts per cubic foot and efficiency of this type of compressor are shown in Fig. 80. It will be noted that this compressor shows a better efficiency than the air compressor at all degrees of vacuum and it is the best reciprocating pump that the writer has ever tested. ”

“ As soon as the cross-head has weakened the field to its minimum value and thus speeded the motor up to its maximum point, a limit switch stops the pilot motor and thus prevents further motion in that direction. As soon as the pump working this at its maximum speed has produced a vacuum in the cleaning system of, say, 12 in. of mercury, the cross-head will begin to move backward and reduce the speed to a point corresponding with the air required. ”

“ By this means it is possible to have several janitors working at the same time on different floors of the building, and each will be independent of the others in his control of the vacuum; although one man may finish and turn off the switch on his floor, the pump will not be stopped if the vacuum is still required by workers on other floors. ”

“ But air pressure cannot force water up even into a perfect vacuum farther than about 33 feet. If your glass pump were, say, 40 feet long, the water would follow the plunger up for a little over 30 feet, but nothing could suck it higher; for by the time it reaches that height it is pushing down with its own weight as hard as the air is pressing on the water below. No suction pump, or siphon, however perfect, will ever lift water more than about 33 feet, and it will do well if it draws water up 28 or 30 feet. This is [pg 20] because a perfect vacuum cannot be made. ”

“ Under any circumstances, whether the air pump is working or not, a certain percentage of the vapor in the condenser is always carried down the pipe B, and this action alone creates a partial vacuum, thus rendering the work of the air pump easier. As a matter of fact, a fairly high vacuum can be maintained with the air pump closed down, and only the indirect pumping action of the falling water operating to rarify the contents of the condenser body. It is customary to place the condenser forty or more feet above the circulating-water pump, the latter usually being a few feet below the turbine. ”

“ The pump piston drives the air out of the pump cylinder which produces a vacuum. The pressure of the atmosphere is about fifteen pounds per square inch of surface. This pressure forces sufficient water up through the so-called suction pipe to fill the vacuum in the cylinder. ”

“ A simple rotary pump is constructed on the principle of creating a vacuum in a rubber tube and so causing water to rise to fill the vacuum. Figs. 3, 4 and 5 show all the parts needed, excepting the crank and tubing. The dimensions and description given are for a minimum pump, but a larger one could be built in proportion.
Through the center of a block of wood 4 in. square and 7/8 in. thick (A, Figs. 1, 2 and 3) saw a circular opening 2-7/8 in. in diameter. On each side of this block cut a larger circle 3-1/4 in. in diameter, having the same center as the first circle (Fig. 3) . ”

“ Pressure gages were connected to the suction, discharge, and condenser inlet, as shown at G, G' and G'' respectively. When No. 1 unit was operating alone the gage G showed practically zero, indicating no vacuum in the suction pipe. Observing the same gage when No. 2 unit was running, a vacuum as high as 2 pounds was indicated, showing that No. 2 was drawing more than its share of cooling water from the main A and hence the circulating pump for No. 1 was fighting for all it received. ”

“ When a high vacuum is attained the efficacy of the pump depends chiefly on the way in which the drops fall on the head of the column. If the fall is too long the drops are apt to break up and allow the small bubble of air to escape up the tube, also any irregularity or dirt in the tube at this point makes it more easy for the bubbles of air to escape to the surface of the mercury. ”

“ It is clear then, that however high the pump may be above the level of the water, the water cannot rise more than 34 feet up the suction pipe, even though all the air be excluded from it and a perfect vacuum formed, because the propelling force, that is, the atmospheric pressure, can only raise a column of water equal in weight to itself, and it is found in practice to be an unusually good pump that will lift water thirty feet. ”

“ Let the delivery valves be where they may, the foot valve will always have some water above it, and the pump bucket will dip into this water, and on lifting produce a vacuum that will cause the pump to fill with water. Notwithstanding that the gland may leak air on the other side of the bucket, this air will in a single acting pump be expelled with the water, but in a double acting pump it will impair the vacuum, and therefore the suction, on the gland side of the piston. ”

“ An electric motor pumps the air and compresses it in a tank. When the pressure reaches a certain point, say sixty pounds per square inch, it automatically shuts off the electric current from the motor which works the pump. But when the motorman uses some of the air to apply the brakes to the wheels, and the pressure in the tank falls below sixty pounds, the electric current is again automatically turned on to the motor.
Of course if an electric motor can operate a pump to compress air it may also work a pump to exhaust air. This is what is done in a vacuum cleaner. ”

“ With a pump such as has been described there is seldom any advantage in fusing an extra connection to the vacuum tube so as to allow of a preliminary exhaustion by means of a water pump. About half an hour's pumping may possibly be saved by making use of a water pump.
The tube to be exhausted is washed and dried by careful heating over a Bunsen burner and by the passage of a current of air. The exhausting tube is then drawn down preparatory to sealing off, and the apparatus placed upon the pump. It is best held in position by a wooden clamp supported by a long retort stand. ”

“ With the rotary pump there are no discharge valves to hold the atmospheric pressure from the discharge side of the impeller and the compression of the rarified air is accomplished by the atmospheric pressure admitting air through the eduction port into the chamber. ”

“ It is economical to combine the pressure [Pg 85] and suction systems by arranging the air compressor to draw air from the vacuum receiver into the compressor cylinders whence it is returned to the pressure line.
Automatic valves keep the pressures in the pressure and vacuum sides of the system within pre-determined limits. “Make up” air is admitted by the automatic opening of an atmospheric valve when the pressure side of the system is low and the vacuum side high, so that the pump is deprived of sufficient air to operate the system efficiently. ”

“ In the inclined position the exhaustion of the vacuum bulb is accomplished along with that of the rest of the pump. The exhaustion of the vacuum-bulb when once effected can be preserved to a great extent for use in future work, merely by allowing mercury from the reservoir to flow in a rapid stream at the time that air is allowed to re-enter the pump. During the first process of exhaustion the tube of the gauge is kept hot by moving to and fro a Bunsen burner, and is in this way freed from those portions of air and moisture that are not too firmly attached. ”

“ Because the putting down of the handle lifts up the piston with its valve closed, thereby tending to produce a vacuum; but the pressure of the air upon the water not contained in the pump, forces more water up into the part where a vacuum would otherwise be formed. ”

“ Plants equipped with vacuum systems frequently operate slightly below the atmospheric pressure, and besides entirely doing away with back pressure on engines and removing the air from the system, there are many incidental advantages in the operation of plants of this character which will lead to a very extended adoption. The principal objection to vacuum systems lies in the fact that the exhausters or vacuum pumps take considerable live steam to operate them, and almost as much in moderate weather as on very cold days. ”

“ If a displacement machine is used as a vacuum producer, the separator must prevent the passage of any dust through separator, which will be determined by holding a dampened cloth over pump outlet during test of apparatus. ”