Document QJZgMM8vb2qkRLo7N9zVN6zy8

cient, some dissolved, oxygen usually remain* and scavengers such as sodium sulphite, iron compounds and certain organic substances must be used to re move the last traces. If not removed, the inhibitors--nitrate, chromates, etc-- may be used to prevent corrosion. Carbon DJoxido. As with dissolved oxygen, free carbon dioxide can be picked up from air. In addition, waters containing carbonates and bicarbonatrs may break down when heated and give oft this gas. Well waters normally con tain more than surface waters. Solu bility of carbon dioxide is greatly influ enced by pH of the solution, the solu bility decreasing with temperature in crease and increasing as pressure goes up. The same method, namely deaera tion, is used for its removal. Because >f its greater solubility, carbon dioxide is more difficult to remove than dis solved oxygen. In feedwater systems and boilers, preventing corrosion from free carbon dioxide, carbonates and bicarbonates is simple. Adding an alkali or a complex phosphate is quite effective. But break down of carbonates and bicarbonates in the boiler liberates fcarbon dioxide, which renders the steam and condensate corrosive. Introducing a volatile al kali' to the boiler or atesm eliminates such corrosion. The amines have been used, and recently organic ammonia compounds were found practical. Ammonia, Encountered rarely un less water is contaminated with sewage, ammonia is very soluble and cannot be removed by ordinary deaeration; In fact, -multiple or fractional distillation is required to get rid of it. Corrosion from ammonia is confined to aon-f^Q rous metals. Fortunately, ammonia'it^i self does not usually cause the difficulty,^* (In this respect there is considerable^' controversy regarding the role of iriJ.J monis in corrosion.) It Is the high p$?( resulting from ammonia presence tlujT* causes corrosion. Consequently, enough is present to raise the pH toO corrosive value, usually over 8.5, tcid^j treatment can be resorted to or emmenii 1 can be removed with a deammonf*i$ Hydrogen Sulphide. This gas rarely!' cause* trouble. As with emmonio it ij? commonly found in sewage-contsoiigj oted waters, although some well wtten/ contain appreciable amounts. Deam$ lion will usually remove most of it. Asi( alkali to neutralize the acidic hydrogel sulphide may also be added under soiwr,- conditions. [ How to Spot Troubles Trouble-ehooting hints from George Holman tell how to in terpret warning signs before a failure causes a shutdown Failures in refrigerating equipment normally warn of impending danger if you know how to read the signs. (These pointers on compressor behavior give distress signals In italics and Hat causes alphabetically.) 1. Uneven vibration fats /leer end piper. Compressor bearing begins to seise shsfl or pin. Do not Stop machine, but slow it down at once. Keep it turning slowly s few minutes, if possible. If bearing is ex posed, spray with oil. 2. Uneven pulsations of compressor. A: If compressor is double-aeitng, valves at one end of cylinder ere out of order. B: Worn or loose bearing, crank, crankpin, etc. 3. Pistons pound as compressor starts. SPOTTING UNUSUAL NOISES in o machine ond Identifying their cause before dom occurs Is one qualification of o good operator. Airy one eon stop a wrecked rnoe*`S A: Oil pump his lost its prime. Bearings ere uncuihioncd by oiL Prime by pres sure adjustment, or by pouring oil into pump. 8: Oil filter Is stepped up. Clean it thoroughly. C: Wriatpins, crankpins, bearings, etc are out of order. ' 4. Quick snapping sound undtr head of enclosed crankcase of tingle-acting com pressor when starting at Jew compression ratio. A: Poppet-typo suction valve strikes safely head. Clean valves and oil system. B: Weak`or broken closing spring^ poppet-type suction vetve. Inspect sod fr place with stronger ipring. $ Ct'Worn stem and dampening pi,0Vj poppet-type euctfen valv^. Replace vffi precise-raachined suction-nlro* cage. D: Suction-valve cage does not getfi Inspect, clean and repair oil system. ) 8. Rapid rat-a-tat-tat of popped valves in compressor. <! A: Evaporator floods and liquid ***] over into compressor. Stop machine^ once. Close expansion valve. Cloa *. (Continued on page 138) I Ob 1402) POWER . Aoll 'y ELECTRONICS FOR THE POWER ENGINEER By F A ANNfTT, Aimfyfs fdfor 5--Photoelectric Tubes Last month we learned how elec trons in tubes are freed by heating the cathode, a process known as thermionic emission. Here we will study how light or photoelectric emission releases elec trons from a metal surface. Tubes for this purpose are popularly known as elcctrio oyea, photocoils, photo tubes and photoelectric tubes. The latter is the name by which these tubes are most commonly known, and will be used in this article. These tubes are applied widely for smoke- and flame-indicating, opening and closing doors, liquid-level control, counting, weighing, and many other purposes. They have an anode and a light-sensitive cathode in a high-vacuum or gas-filled bulb. Their cathode Is usually aemicylindrical, Pig. 2, costed with a light-sensitive material soch as oxides of cesium, bar ium. sodium or potassium. Their anode is usually a straight vertical wire, sup ported in the tube's base. It is partly surrounded by the cathode and made as small as permitted mechanically so as to cast the least possibla shadow on the cathode. A light beam is focused on the cathode, as in Fig. 3, which causes electron* to flow to the anode, when a potential is applied across the two. t-hjhf-Sanritlve Metoli.At this point we wijj consider why some metals are light-sensitive. They are for the`tame tesson that certain metals are good con* Lt May 1948 Power,- p 105, *e learned that the atoms of the best conductors, copper ond silver, have each a single electron In their outer , > located well away from the nu cleus. The single electron of each atom is esiuined to be held loosely and is infenced by ed/aceat atoms. In this ***! l* free to move about at random ^nt! bought under the influence of v tage, when it drifts slowly from the Ike positive 'terminal of ,he circuit riaAl*mit ong the most light-sensitive mate- te the alkali metals, lithium, Light-Sensitive Atoms /'XN '-------ytvtievt' \ Lithium \ / /" 'Oc\ \ \ \ V-'V ' /\ gf i s, _______ \ s-- ^ . X ____\ / ^ 'V'^yv,*we,u y ^\ \V <-:>>// V'vVv^.'V//1 Among the most light-sensitive materials ore the olkali metals---lithium, so dium, potassium, rubidium and cesium. Light sensitivity increases in order named sodium, potassium, rubidium and . cesium oxide over which is an exceed cesium. Electron arrangement of each ingly thin deposit of cesium. Such a is shown in Fig. 1. As would be ex construction improves the light sensi pected, lithium is the least light-sensi tivity of the cathode. tive, the single electron in its outer or Photoelectric lubes with such a cath bit being the closest to the nucleus of ode are particularly suitable for uN all five elements. On the other hand, with incandescent lamps, os they are 10 cesium, which has the' single electron to 100 times more )ight'.*ensitivo than in its outer orbit farthest from the those with other practical cathodes. nucleus, is the most light-sensitive. Such tubes are sensitive to the seme Unless there is some reason for doing light as the human eye and are used in otherwise, cesium and its oxide* are color matching. They are also used in. most generally used for the cathode most industrial relays that operate on coating of photoelectric tubes. Such a the interruption, diffusion, deflection, cathode may have a silver-plated cop reflection or refraction of a light beam. per base covered by s thin layer of Alkaline earths--barium, strontium, POw* *1 Auguit 1948 (493) 107