5. 1.LEWIN, N e w York University, Washington Square, New York 3, N. Y.
T h i s saies of articles presents a survey of the basic principles, characteristics and limitations of those instruments which find important applications in chemical work, running the gamut from balances and burets to servomechanisms and spectrometers. The emphasis is on commercially available eqnipment; approximate prices ore quoted to indicate the crdw of magnituh of cost of ti@8arious types of design.
In choosing a vacuum pump, the following factors should be taken into account: (1) size of the system to be evamated, (Z) final, or blank-off, pressure desired, (3) required rate of evacuation, presence of condensible vapors that and (4) will pass through the pump. For vacuum distillations, pressures lower than 0.1 mm Hg are rarely required, the volume being evacuated is relatively small, and cold-traps can he employed to protect the pump from the vapors released in the system. Therefore, an inexpensive, single-stage rotary pump is perfectly adequate for this application. I n fact, in thosp applications where the pressure necd not be reduced below about 15 mm Hg, the water aspirator pump is the instrument of choice. If convenience of manipulation is of paramount importance, the cold-trap, with its attendant annoyances, can be dispensed with by using a vented rotary pump in whioh fairly high concentrations of vapors from thc system can be tolerated wit,hout damage to the pump or its ail. In the handling of gases for research and analysis, pressures of the order of 10 microns Hg are usually required. These are readily obtained by a two-stage rotary pump, or by a diffusion pump backed by s. single-strage mechanical pump. If the gases under study are reactive or corrosive, it is necessary to protect the pump by liquid nitrogen traps placed between the system and the pump. The size of the pump unit chosen will depend upon the volume of the system to be pumped down, and upon the rate of release of gas in the system by dpsorption, reartion, pyrolysis, or leakage. The speed of a pump determines the rate a t which t.he pump can loner the pressure in a given system. For example, it can be estimated from the equations given p r p vioudy that the time needod for a pump of speed 1 liter/sec connected to a 10-liter flask through a tube 50 cm long and 1 cm in radius to reduce the pressure from a& mospheric (760 mm Hg) to 10 microns Hg is about 4.5 minutes. A pump capable of reaching the same vacuum in half thia time (2.2 min.) would need to have a speed of 4.35 liters/aec (or more than four times greater). This illustrates the fact that as
the speed of the pump is increased, the limiting factor may soon become the speed (conductance; admittance) of the tubing and apertures connecting the system to the pump. (In the example given, this was estimated a t 2 liters/sec, oalculated from the formula ST = rJ/l. However, that, formula applies only in the molecular flow region, i.e., below about 10 microns Hg. Above 10 microns Hg, other formulas based on the equations for viscous flow should be employed.) Hence, i t is important to judge the speed of the tubing and assaciated apertures (e.g., stopcocks) in the vacuum line of the apparatus, in order to avoid using an unnecessarily expensive pump where its high speed would be ineffective. Tables, formulas and nomographs far estimating the speeds of various configurittions of vacuum line plumbing more accurately than was done above will be found in the references cited in the bibliography. Central Scientific Co., Chicago, sells a "Vaou Rule" (No. 94008, $1.00) which permits rapid cdoulations of tube eonductances to he made, and contains conversion fact,orsand tables useful in vacuum work. Another important consideration involved in the choice of a pump, partioularly in a dynamic system, is its throuyhput. This is the quantitr of gas passing through the pump per unit time, as oontrasted to the speed, which measures tho volume. Throughput (Q) is defined in terms of P V, and many he expressed in units of mm-liters/min., microns-litera/sec., or other such units. I t will be recalled that the speed of a rotary pump decreases slowly as the intake pressure is lowered, then falls off rapidly toward zero in the vicinity of the ultimate, or blank*ff pressure. The throughput, however, decreases steadily and markedly over the entire useful range of the pump. Since: Q = P.V/T
and
S
= V/T,
it is evident that Q will decrease linearly with P over the range where S is spproximately constant, and will fall more rapidly where S begins to drop off toward zero. The blank-@ puwssure observed in any system is det,ermined by the point where
feature
the rate of release of gas into the system equals the throughput of the pump. If the rate of release of gas into the system is large, due to leaks, gas-producing reactions, etc., then low pressures can only be obtained by t h e use of pumps with corre~pandinglylarge throughputs. Hence, in a static system (no leaks, no continual gas release) pressures as low as the ultimate pressure of the pomp can be obtained with pumps of any speed, if one can afford to wait long enough. That is, the minimum pressure attainable is determined only by the ultimate pressure of the pump, and is independent of the speed. In a dynamic system, however, the minimum pressure is determined by the throughput of the pump, and therefore by its speed. In laboratory work involving the spectral properties of gases, electron tube construction and properties, ionization phenomena, etc., pressures lower than 1 micron Hg are usually needed s t some s t w e of the work. Diffusion pumps hacked by mechanical roughing pumps are generally employed. In such applications, it is important to recognim that the roughing pump must he matched to the diffusion pump. That is, its throughput most be a t least equal to that of the diffusion pump a t the pressure a t which the latter has its m ~ x i m u mspeed, so that the roughing pump will be able to maintain the proper fore-pressure for the diffusion pump. In vacuum-drying work, whether a t elevated temperatures (vacuum ovens) or reduced temperatures (freez~driew), the requirement is for a. pump capable of maintaining pressures of the order of 0.1 mm Hg (vapor pressure of ice a t O0C = 4.6 mm Hg), with a large throughput, and suhjest to the passage of considerable amounts of water vapor through the pumping chamber. Large capacity, vented (i.e., gas ballast) rotary pumps are the instruments of choice for this type of application. Certain types of work call for the production of pressures in the sub-millimicron Hg range of pressures, and the multistage fractionating oil diffusion pumps are most convenient and appropriate here. In some cases, s. "booster" diffusion or ejection pump must be used between the diffu~ionand the roughing pump in order to make possible the matching of througbputs a t the different intake pressures suitable for these latter two units. In some applications, a11 traces of pump vapors must be kept out of the system being pumped, and in these instances the malecular drag or evaporated metal typw of pumps find their special utility. The following sections describe the depign features of the various commercial (Continued on page A434)
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Chemical Instrumentation pumps currently available. The discussion is limited to those instruments that have proved to be especially useful in laboratory-scale work. Wherever ultimate or blak-off pressures are cited in the following paragraphs, these data are being quoted from manufacturer's literature. I t must he recognized that these pressures are meaaured under the most favorable conditions possible. The system being evacuated is small and has been outgassed, the pump is new, and the oil is clean and free of volatile oontaminants. Furthermore, such pressures are almost always measured with a McLeod gage, which gives only the partial pressure of the non-condensible gases in the system, and does not respond to the partial pressure of pump oil or other condensible vapors. Also, if a cold-trap is used between pump and gage, the ultimate pressures obsewed will he several orders of magnitude lower than in an untrapped system. I t is extremely unlikely that a mecbanicd pump will produced a totol pressure of less than a few microns in an untrapped system if it has been in use for some time. For pressures lower than 1 micron, it is generdly necessary to employ a diffusion pump backed by a mechanical pump, or a twa-stage mechanical pump with a well designed cold-trap between the pump and t.he system. The reader should also be cautioned against confusing the units of aped given for different types of pumps. I t is rommon to cite the speeds of mechanical pumps in liters/minute, whereas the speeds of vapor pumps are generally specified in liters/second. It will be noted that the speeds of diffusion pumps appear to be extremely large compared to mechanical pumps. However, the former refer to exhaust pressures of the order of tenths of a millimeter Hg, whereas the latter refer to atmospheric pressure. On the other hand, the throughputs of diffusion pumps at their operating pressures tend, in many eases, to be smaller than those of rotary pumps in tbeir appropriate operating ranges.
C e n h l Scientifle Co. The Cenco line of rotary pumps covers s. large number of speeds and pressures, ranging from a portable hlower and vacuum unit (No. 93971, capable of amaximum pressure of 25 psi, and a maximum vacuum of 27 inches Hg, speed 1.3 cubic feet/min., $71.50) useful in vacuum filtrations or as a source of compressed air, to an extremely high throughput, high-vacuum pump (Hypervac 100, ultimate pressure 0.1 microns Hg, speed 960 liters/min at 1 atm., $2250) capable of maintaining a hard vacuum in a large spectrograph, metal refining furnace, etc. The Pressovao 4 (No. 90510, $99.50) is a single-stage, ail-ealed rotary pump with a ~ingle,spring-loaded radial vane which rides an the ecceutricslly-mounted rotating cylinder, an illustrated in Fig. 12. If the intake line is open to the atmosphere, and the exhaust line closed, pressure can be built up in the latter to 10 pounds per square inch, so this pump can
A434 / lourno1 o f Chemicol Education
be utilized a source of moderate amounts of campremed air. When employed as a vacuum pump, this device has a speed of 35 liters/min, and cea hold a pressure as low as 15 microns Hg. This pump 18 useful far vacuum distillations, backing:of diffusion pumps, and other laboratory applications that call for a relatively inexpensive pump giving moderate vacuum. I v
Figure 12. Derign of the Cenco Presovac and Hyvoc mechanical pumps.
All the other Cenco rotary pumps are two-stage devices. The original Hyvac series contained two of the spring-loaded, single-vane eccentric-rotor stages, of the type just described, connected in series. This pump attains an ultimate pressure of 0.3 microns and has a speed of 10 liters/ min (Model Hyvac, $115). The new Hyvac 2,7 and 14 series pumps are of two-stsge, internal-vane construction, having vane8 spring-loaded in a rotor which is placed ooncentrioally on the pump shaft. The stator is offset so that rotor contact i~ a t the top through a film of oil which provides the seal between the intake and exhaust chambers of each stage. This design is similar to that shown in the illustration of Fig. 16. The Hyvac 7 (0.1 micron Hg, 70 liters/min, $285) and Hyvac 14 (140 liters/min, $375) are provided with the gas ballast feature. Using gas ballast, the lowest pressure attainable is 10 microns Hg, compared with 0.1 micron when the gas ballast valve is closed. When gas ballast is being used, the pressure in the exhaust line of the pumping chamber is higher than without bdlast, and a small amount of leakage into the intake line is responsible for the higher level of ultimate pressure In the Hypervac series of pumps, the two stages are unequal in size; the secondary, or roughing stage is small, and the primary, or finishing stage is large. The construction is suoh that the greater portion of the pump oil remains in the rouehine staee. so that eases absorbed in 11," I,? rcmovch l.ew I,cfc>?cthe bil enters the fiuirhiw ctncc. TIw Ilypcrvai. ~r mlps give p r e s ~ u r c wmpnr:ihlc ~ with the Hyvac instruments, but a t considerably greater speeds. For example, the Hypervac 4 ($195) gives 0.3 microns and (Continued a page A486)
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Chemical Instrumentation -
has a speed of 41 liters/min; Hypervaa 25 ($650) gives 0.1 microns and 264 liters/min. Cenco also produces a one-stage, steel, mercury diffusion pump (Supervac, 10 to 15 micron Hg forepressure, 10-' mm ultimate pressure, 7 liters/sec a t 10 microns, $95 with heater), and a threeatage, metal, oil-diffusion pump (Supervac OD-25, 0.1 mm Hg forepressure, 5 X 1 0 ' mm ultimate pressure, 28 litera/see s t 0.1 mm Hg, 8155 with heater).
W. M. Welch Scientific Co. The rotary pumps manufactured by the Welch company also come in a variety of sizes, and have found wide application in laboratory ~ o r k . I n the Welch pumps, the rotor has spring-loaded vanes, and is mounted so that its upper surface always touches the same place on the inner surface of the stator, this point being between the intake and exhaust ports so that the contact serves to seal t,hese ports from each other. The basic design is similar to that shown in Fig. 16. A very convenient single-stage, ventedexhaust pump for vacuum distillation applications is the Welch Dist-O-Pump ($107) which gives 15 microns H g with the vent cloaed, and has a speed of 35 liters/ min a t atmospheric pressure. A ronventional pump capable of serving as n source of both moderate pressnres and vacuums is Model 1410N ($115), d i c h can give up to 15 psi in the exhrtunt. line, and a vacuum of 20 microns working against atmospheric pressure. The speed is 21 liters/min. Another conventional singlestage pump designed for vacuum distillation work is Model 1404H (%150), which is not vented, pulls a vacuum of 20 microns Hg, and has a speed of 33.4 liters/min. All other Dumns in the Welch line art. + designed for lower pressure applications, and utilizc an unique feature called tho "DuoSed." This consists of a by-pass channel provided close to the seal hetween the rotor and the stator. As the van? sweeps gas out into the exhaust, the last increment of gas which may fail to be pushed out of thc rshanst valve escapes into this channel, where it stays until the addhion of similar increments of was in
.
have an ultimate pressure of 5 microns Hg; with two of these stages in series, ultimate presnures of non-condensablen as low as 0.05 to 0.1 microns Hg are possible. Examples of the single-stage pumps are Models 1406H (6150) with a speed of 33.4 liters/rnin a t 1 atm., and 1403B ($245), which pumps 100 liters/min. Two-stsgo pumps are svdltble ranginr from a speed of 21 liters/min (No. 1400B, $133) to 375 liters/min (No. 1397B, $845). Tht? two-stage models a,re $1 wailable with vented exhaust; when the vent is used, thr dtimate pressure rises t o the mder of 1 micron Hg.
Nelson Vacuum Pump Co. This company, the Fen. F. Ne1.m Vse-
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Jdurnal of Chemical Educotion
uum Pump Co., Berkeley 10, Califovtlia, manufactores a selection of inexpensive, single-stage ~.ot.arppumps for laboratory applications. Tho pumping chamber rontsins an oval rotor which rotates inside a concentric stator. Two spring-loaded braas vanes ride upon the surface of the rotor to form the gas seals, as shown schematically in Fig. 13. This arrangement has the advantage that any wear of the vanes is ai~tomstieallyeompcnsstetl for by the spring-loading. Also, any nhmsive matter t,hst is drawn into the pump through thc intakc part ie cleaned off t,he rotor by t,hc exhaust vane. A check valve at the intake port seals the vaeuum line connection so that oil cannot back up into the systom if the pump is stopped while still connected t,o the evacuated chamber. These pumps have ult,im;tte pressures of 10 to 15 microns Hg, :md speeds oi 24 to 36 lit.ers/min a t I st,m.
Figure 13. De.ign of the Nevaso rerie. of pumps (Nelson Vocuum Pump Co.1
Model 1)21 ($104) can he used as a source of pressure up to 50 p ~ i ,and vacuum down to 0.01 mm Hg; Model 027 ($109) is equivalent, hut with a built-in copper coil for the cilwlation of cooling water to maintain t,he pumping chamber coal, regardless of the ambient temperature. Models 011 ($99) and 924 ($105, watercooled) are intended for vacuum use done. Model 935 ($120) is specificdly designed for vacuum difitillation work.
Precision Scientific Co. This manufacturer hm recently entered the vacuum pump field with s two-stage, internsl-vane rotary pump capable of an ultimate pressure of 0.1 micron Hg, and a speed of 75 liters/min a t 1 atm, and of 49.2 liters/min s t 0.5 miemn Hg. The details of construction, including the oilsealed Teflon exhaust valvo, the two rotors mounted on a common shaft, and the intrakc trap chamber to remove dust and solid particles from the entering gas, arc ahown in Fig. 14. The two spring(Continued o n page A4S8) Volume 36, Number 8, August 1959
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Chemical instrumentation loaded sliding vanes in each rotor are not s h o r n in the diagram. A larger capacity pump of the same design is also available (Model 150, 0.1 micron Hg, 150 liters/ min, 5360). Langmar Corp. Another recent addition to this field is the Langdon pump, manufactured by the Langmar Corp., Chicago 39, Illinois, and designed spcoifieally for vacuum distillations. No attempt is made to achieve very low pressures by precise machining of the mechanical parts, or to protect and preserve the oil. Instead, a rotor with Teflon vanes sliding outward under the influence of centrifugal force (i.e, not, apring-loaded) rotates s t relatively high speed (1725 rpm direct-coupled to t h r
motor, as contrasted with about 300-500 rpm in most other pumps, obtained by a pulley-and-belt drive from the motor) to give an ultimato pressure about 0.02 to
Figure 14. %hernotic drvwing of the Precision Scientific Co. two-stage internal "one pvmp.
On11 50 ml of ordinaryauton~otivt;lubria,ating oil i s used, and the oil ehrvge is replaced every day, or after every run. These design features are intended to eliminate the deterioration of pump performance caused by the absorption of organic vapors during vacuum distillntions. Thus, the Teflon vanes cannot, corrode and do not tend to pick up gummy material from the ail and stick in their slots; since there are no springs, thesc components cannot fail due to corrosion or fatigue. The oil is inexpensive and thp frequent changes eliminate problemsduo to contamination. This pump is designed fut. maximum useful life under adversr chemicel conditions, rather than far high pumping efficiency and law ultimate pwssure. An exploded view of the Langdon pump is shown in Fig. 15. The pump is priced at, $225.
0.05 mm Hg, and a speed of 30 litela/min.
Figure 15. Exploded v i e r of the component ports of the Langdon vacuum pump.
Leybold The German firm of E. Leybold's r a e h f o l ~ e rmanufilcturen rotary gas balIut pumps, most of which are available in the U. S. through NRC Equipment. Corp., Newton 61. Mans.. and A . S.
Figure 16. Design of the Leybold ringle-rtoge rotary vane pump. 1. Cylindrical caring; 2. Eccentric rotor; 3. Vaner 4. Gar ballast inlet; 5. Oil-immersed exhaust volve; 6. Baffle; 7. Oil dipstick; 8. Exhaust port; 9. Intake port; 10. Dirt trap; 11. Intake channel.
Lapine and Co., Chicago 29, Illinois. Thc laboratory-~calepumps are of the springloaded, rotary vane type. During thc exhaust cycle, the vane opena a v e n t to the atmosphere, letting some air enter t,he pumping chamber. The air plus gns (Continued on pnpa A440)
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Chemical Instrumentation from the system is then ejected through the exhaust valve by the continued rotation of the rotor. Some of the details of construction of Leybold singleestage gas ballast pumps are shown in Fig. 16. Model 2S (5160) is a single-stage pump with a speed of 35 liters/min, and an ultimate pressure of 2 microns HE with the gas ballast shut off, 0.6 mm Hg with gas bnllast open. Model 6S (5325) is similar, but with a speed of 190 literdmin. Examples of two-stage pumps are Model 211 (S215), 33 liters/min, 0.02 microns Hg without ballast and 10 microns with ballast, and Model 6D (5375) with 190 liters/min.
NRC Equipment Corp. A number of mercury and ail diffusion pumps is manufactured by the NRC Equipment Corp., Newton 61, Mass. The construction of s typical three-stsge, fractionating diffusion pump of their manufacture is shown in Fig. 17. Representative of these pumps are Model A2P ($165) which is a 2-inch, air-cooled pump having n maximum speed of 80 liters/seo a t 8. forepressure of 0.2 mm Hg, and Model H4P ($235), speed 340 liters/sec a t 0.25 mm Hg. One of the largest vapor pumps eommereially available is NRC's Model H32P ($32501, which has a 32-inch intake aperture, and a speed a t 30,000 liters/sec a t a farepressure of 10 microns Hg. .In example of a molecular drag pump is
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shown in Fig. 18. A light alloy disc, 31 cm in diameter, revolves a t high speed (6000 rpm) between two forged plates which have spiral grooves whose size increases with the radius. The gas intake is a t the oenter, the exhaust a t the periphery. The tolerance between disc and plates is 8 few hundredths of a millimeter.
replaceable titanium evaporation source that can be mounted in a, static system to reduce the pressure below that produced by the pump system. If m ionim-
Figure 18. Compo~ent parts d o molecular pump by Beoudouin, Paris. Motor it o t left; rototing metal disc is ot right.
Figure 17. Design of on NRC three-rtoge frodionoting metol oil diffurion pump.
The rotating disc imparts momentum to gas molecules entering from the system, and impels them toward the exhaust. This pump is manufactured by Besudouin in Paris, and is distributed in the U. S. by NRC. Blankdff pressure is mm Hg when the forepressure is 2X 2 to 4 mm Hg; speed is 60 liters/sec a t mm Hg; price is $1895 5 X This company also offers a Titanium Adsorber Pump Assembly ($215) which is designed to provide a small, oanvenient,
tion gage is mounted near the titanium cartridge, the ions it produces will markedly improve the gettering effect, and will produce vacua. in the 10" to 1 0 - k m Hg range. (An ionization gage alone, without the titanium source, will be extremely effective in gettering a small, static system. This is called "ionpumping.")
CEC Rochester Division The largest and most diversified line of high vacuum vapor pumps and ultrahigh vaouum pumps currently available is manufactured by Consolidated Electro(Continued o n page A4421
Chemical Instrumentation dynamics Gwp., ICucheatar Uiviuian, Rochester, New York. Their products include gless as well as metal pumps based on mercury or on oil pump fluids, and also a unique gettering pump. The main features of construction uf CEC metal jet-type pumps are illustrated in Fig. 19. .4 non-fractionating, threestage pump is phnwn in Fig. 19 A . The I
Figure 19. A. Design of o non-fractionating lhree-stage vapor pump by CEC. B. Some pump, modifled for froctionation.
stream of vapor expands on passing through the jet openings, and the stream projects downward a t supersonic speeds. Molecules diffusing into the pump collide with thme streaming molecules and are propelled downward with them, resulting in a compression to a pressure a t which the fare-pump can remove them. The Model MB pumps are two-stage, Model MC arc
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three-stage metal devices of this type. For example, MB-I0 ($75) is a l-inch pump (i.e., the aperture a t the intake is I-inch), has a speed of 13liters/sec, and an ultimate pressure of 0.2 microns Hg. Model MC-275 ($177) is a. &inch pump, has a maximum speed of 200 liters/see, and an ultimate pressure of 5 X 10-f mm
devioos, and are impracticd where very large speeds are required. A typical glass fractionating pump is shown in Fig. 20. Model GF-20 ($225) is mch x twoo,,-Fi,,np Port
n
m.
A fraotionating-type pump is shown in Fig. 19 B. In this t,ype of instrument, the pump bailer is divided into compartments which communicate with each other through small holes. Because of the restriction these holes offer to free mixing of the pump fluid, the more volatile constituents tend to concentrate in the outermost chamber during a run, closest to the exhaust line, while the least volatile fraction of the pump oil concentrates in the central chamber, so that the lowest vapor pressure vapors issue from the jet nearest the system. An example of a pump of this kind is the Model MCF-60 ($147), which has a 2-inch intake, a speed uf 66 liters/sec, and an ultimate pressure uf 5 X 10-7 mm Hg. The smtlllest of these pumps is Model VMF-5 ($81), which has only two stages, a specd of 4.5 liter/sec, and ultimate pressure of 1 X mm Hg. There are available glass oaunterparts for the smaller models of the metal diffusion pumps. Glxss is to be preferred if the lowest possible pressures m e required, far i t is easier to outgas a glass appssatus completely than to do the same for rt metal apparatus. However, glass pumps are more fragile and expensive than the motal
Figure 20. A two-stage gloss froctionoting oil pump by CEC.
stage, water-cooled, fractionating pump: it has a speed of 26 liters/sec, and ultimatv presmre of about 1 X 10-' mm Hg. A modification of the diffusion pump ib the so-eelled ejector pump, illustrated in Fig. 21. This is the besic design of the Model KB series of instruments, which have very high speeds in the pressure range 0.3 to 0.02 mm Hg, where mechanical pumps operate a t low efficiency. Thc oil vapors undergo an expansion upou issuing from the jet, and achieve great velocities. Gas molecules diffusing into the pump are entrained by the vapor stream, which then passes into the funnelshaped diffuser, where compression ocours. Tho compressed pump vapors condense, aided by the cooled surrounding walls, (Continued on page A099)
Chemical Instrumentation
becomcs salwxted. fresh lavers me dr-
addle the compressed gas is pumped off by the mechanical roughing pump. Model KB-150 ($1075) has a maximum speed of 190 liters/sec, and an ultimate pressure of ahout 1 micron Hg.
Figure 22. Schematic diogrom of the design of the CEC Evopor-Ion titanium pump. Figure 21.
A CEC ejector-type vapor pump.
The Evapor-Ian pump (WOO), which based on the gettering principle, is shown diagrammatically in Fig. 22. Titanium re is continuously fed onto s post heated by electron bombardment from the filament. The titanium evaporates and upon striking the oooled pump wall condenses in a thin layer. Moleoules of oxygen and nitrogen entering the pump chamber comhine with the titanium and are removed. As each layer of t,itanium is
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The Hcraeus-Routs pump, which cuotains tw dumhholl-shaped rotors operating a t high speed in an oil-free chambet. (cf. Fig. 3) is hasically a blower deviet and serves best to baok :L diffusion pump. or to serve as a high-capacity booiitm between a diffusion pump and a rotary roughing pump. This type of pump comes in models with ~ p e e d sranging from 35 to 1600 litrrs/sec. Since there is no oil in the pump, and no actual contact between rotors and stator, the internal friction is (Conlinued on page A448)
Chemical instrumentation mall, and a. preanwe d~tllwti:tl ot s few millimeters Hg i~ sufficientto turn the rotors. Prices range from 53125 to $18,130.
Kinney Manufacturing Div. One of the biggest manufacturers of large-scale meohrtnical pumps is the Kinney Manufacturing Division, New York Air Brake Ca., Boston 30, Mass. The smallest of its single-stage, mechanical pumps is Model KS-13, with a speed of 370 liters/min, an ultimate pressure on the MeLwd gage of 10 microns Hg, and a price of $598. Larger pumps are available with speeds up to 22,000 liters/min (and prices to $8000). The smallest compound pump is Model KC-2, with a soeed of 57 liters/min, ultimate p-csanrr
of 0.2 microns Hg, and price of $!!B2. A11 the Kinney pumps m e provided with gas ballast. The Kinney pumps differ from other makes of mechanical pumps by having a hollow piston attached to the rotating cam. This hollow piston slides up and down in a special slide pin during rotation of the cam, and has openings cut on the inlet side to provide a large and direct opening for gases to diffuse into the pump cylinder when the inlet port is uncovered. This helps in achieving the maximum speed of the pump. A complete line of booster and vapor pumps, both fractionating and non-frartionating, as well as other vacuum instrumentation, is also offered.
W. 8 W. Manufacturing Co. A small, handaperated pump that is very useful to have in n. chemical lahora-
tory is the "Golden Thief" of W. and W. Manufacturing Co., P. 0. Box 9311, Chicago 90, Illinois. This is a pistonand-check-valve device, built on the same principle as the familiar hicyole pump. I t is intended mainly for use in the sampling or transfer of liquids. The pump end is screwed onto the neck of the container (bottle, can, etc.) that is to be filled. Air is extracted from the containel. on the upward stroke of the plunger, causing liquid to be drawn or siphoned into the container through a tube that dips into the liquid and enters the side of the hafie of thepump. Theliquid pumped does not enter the pump cylinder and henee does not contact any of the moving parts. Various model8 are available in brass, aluminum or stainlesfisteel :hi prices rnnging from $12.50 to 873.
Other Companies A number of other manufaoturers offer pumps t,hitt m e useful in laboratory work, and that embody the design features already described. A prominent manufacturer of large-scale mechanical pumps for industrial use is the F. J . Stokes Corp., Philadelphia 20, Pa. Diffusion pumps of the various types described are available from the following manufrtcturers: H. S. Martin and Co., Evamton, Illinois; Arthur F. Smith Co., Rochester 4, New York: Vacuum Instrument Co., Huntington Station, New York; Veeco Vacuum Corp., New Hyde Park, Long Island, N. Y.: and Eitel-McCullough Inc., Ssn Carlos, California. A new titanium pump, called the VacIon, is currently being produred hy Varian Associates, Pnlo .4lto, C:diforni:t. Bibliography I)CSHMAN, S., "Scientific Foundations' oc' Vacuum Technique," J. Wiley and Sons, N. Y., 1949. G ~ H R I EA,, , AND WAICERLING, R. K., "Vxuum Equipment and Techniques," McGraw-Hill Book Co., N. Y., 1949. "High Vacuum Pumps, Apparatus and Accessories," Bulletin IOG, Central Scientific Co., 1700 Irving Park Road, Chicago 13, Illinois, 1958. "High Vacuum Vapor Pumps," Bullet,in 0-1, Consolidated Electrodynamicr;, Rochester Division, Rochester 3, N. Y., 1958. SULLIVAN,H. M., "Vacuum Pumping Equipment and Systems," Reu. Sci. Instr., 19, 1-15 (1948). "Vacuum Pump Size Determination," in Bulletin P3, NRC Equipment Corp., 160 Charlemont St., Newton Highlands 61, Mass., 1956. VANAm*, C. M., "The Ilesign of High Vacuum Systems and the Application of Kinney High Vacuum Pumps," Kinney Manufacturing Division, New York Air Brake Co., Boston 30, Mase. J., "High Vacuum Technique," YARWOOD, J. Wiley and son^, N. Y., 3rd Ed., 1955. in /hi9 s m r v !rill d ~ ! ~d i r h prinnplps oj drsirp ond chornrlmLnlU~.oj' perJor?nnner oj cornrmriol luhnmlor,. T h e s r ~ srlzrle l
l h
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