for use by evaouating it while i t
&nd, are perhaps the mwt satisfaotory ressurekiasurin de VI-. They are simple and accurate, d d o not require e s k h r i tion against a stsndsrd. To keep them readable, they should be protected by traps chosen to exelude dirt and corrTive fm?. A little care in ohoosing and installing proper tra wdl spprecrably lengthen the useful life of manometers,and wirresult in more ~ceuratereadings and worth-while savings in roplrroement casts. A w o w m age useful over the range from %bout25 mm. dawn to 1 mm. is &e float-type manometer, sometimes known ss the DuBrovin gage. Although this kind of manometer is old few chemists and chemical engineem are nequainted with it. F. 0. E. C~rmnnnandK.A.Ga~osdiacusseditsooerating principles in iN;USTRIAL A N D ~ k c l ~
15. 285 (1943). Bhoflv. this t Y D e of ma-
nometer,'one 'form of "Ghieh i; 'shown in Figure 1, consists of-B tube with one end closed. inverted in B somewhat larger tube whioh'is a little over twice i t s own length and is half full of mercury. The float IS eentered in the lerger tube by two sets of three projections, one at the top and one s t the bottom. This type of gage 1s prepared
i8 in a horizontal position and bringing it to a vertical position while evscusted. This is the zero pressure poaition of the float. When the pressup in the spaoe above the float is increased, the float sinks lower mto the mercury untd the downward pressun on the flost is Counterbalanced by the upward force of buoyancy on its submerged por. tion. The Aoat of a gage like that shown in Figure 1 moves 7 mm. for n 1 - m . change in pressure if it is made of 13-mm Pyrex tubing with a 0.4-mm. wnll. This t y of manometer har been found useful in plant operations invocing prwure down to 1 mm. It can be eagily made by a moderately skillful glssp blower, eves a oontinuous indication of the total pressure in the system, including that due to condensable vapors, and can br easily read to 0.1 mm. A commercial variety of this B e, known 84 the DuBrovin gage, can be obtained from the I $ Welch Scientific Co., Chicapo. The M O M age serves to meaSure ressurea from about 5 mm. down to a%action of a micron. hthough it is generally considered B primary standard for the meagurement of low pressures in the laboratory, it suffers from disadvantages whici mske i t inconvenient for plant use. One of these is that th$ readings are not continuous; to obtain readings, the mereur) must he raised to compress the gas in the bulb into the enpillary then lowered to allow pressure equilibrium between gage and s s tern to be established neein. Another is that oondensegl; vapors and gases which dgviste from the gas law are not. oor. rectly measured. However, when its faihngs are known nm tsken into account, it is often quite useful. A convenient com. act form of M c W gage is made and sold oommercially b) J. Stokes Machine Co., Philadelphia. This gage is ohtsinabb in three ranges, 0 to 5W0,O to 700. snd 0 to 70 microns. The Pirsui type vacuum age messures as pressures by de termining the thermal loss B heated l!lment. Since thi: thermal loss is E function of the pressure of the g84 around th< filment. it oan be wed to indicate eas mesure. The us&
give a oontinuous indication or even record add con&l D N ~ Y U in~B~svstem.
box hy a-S-foat cable. The portsble eontrol box contains twt meters. one to indicate bridse v o l t m and thk other eelibrated in pr&ure un;t in two ranges, 0 to 20 microns snd 0 t. 0.75 mm. Additions1 pairs of mstchei
tubes can be supplied so that the pressm mn be read at more than one point o! the vacuum system. The range of th instrument can be varied to include PM mres as high as 3 to 4 mm., provided adjustments are made in the type c tube used and the scale range. The Televac type MR vacuum re corder distributed hy Precision Seientifi Co. &Chicago, is arecording Pirani with a range of o to 500 microns. record is produced by 8 Lee& & Northru Mieromax strip chart reoordsr with s y l pr-ureseale. The makers stat t at the instrument is extremely stab1 under all conditions due, primaril t 8pe*ally treated filaments m the
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 37, No. 3
P-w in the range from to lo-' mm. can best be measured with an ionisation gage. The ionization gage consists of B yacuum tube with filament. arid, and plate, omvided with s tubulation for attaching i t to the-wiaum yi&& In operation, electrons o d n e from the filament to the mid. which ~ N B88B
standard Moore packless, fiexible shaft type, li uid level contmller with all wluch come in contaot with t?ne &id d e of HBSteUov .oonstruction immrts a hi& deof corrasion &tame. F i m 3 shows B mom of thee controllers. The motion of
gm,thz p i t h ion e u m n t is propoCtioml to the gas m u r e in the gage. P-w measurements with this gsge are t!ereiore made by measuring electrical currents. The Distihtion pmducts type HGZOO gage is 8 typical cammenial ioniebtion manometer. It incornorates a power supply for the ionization tube, B Gntml circuit to keep the electron current eonatant and an amplifier for measuring the ion eumnt. it cavern the complete rs to lo-* nun. The model S??elevrx distributed by Precision &entifie Co. is a premure recorder using both e. Pirsni snd sn ionisation gage. From atmospheric prpasure down to lo-' mm. the instrument records pressure 88 indicated by,the Pirani tube. At that ~ - u n t the recorder tnoa a relay that mskea it k i h l e to turn on the ioiization &ge which serves to record D-w from 4 X lo-' down to lo-'
seotion,'ae the photogmgh sho?s. Manufactwe of a device such 88 this fmm Hastelloy 18 quite a manufacturing aohievement. These controllers are also availsbie in neoprene-covered and in ruhber-eovered construotion, among other types.
Moore Products Go.. Phitadelohis. bas just Figure 3.