Document 8R80yz6bn8DO1DyRMGBxbvvOe

NEW LOOK continued of iho two typos o( sir systems for a plant using 1000 c(m at 100 psi. On a typical job. this oir is needed in four areas: 300 cfm in assembly room, 300 cfm in sandblast and point, 200 cfm in testing, 100 cfm in shipping--snd 100 cfm for day maintenance work. Looking over the table you see that the typical unit system has lower initial cost. And there ore other advantages --detailed below. less Pressure Drop. Load centers use small wires, high voltage for power transmiasion to substations. Since core* pressora in the unit system are ctose to the load, small pipea with short runa transmit sir with low pressure loss. Presaure drop in air lines is a func tion of pipe length, diameter, sir quan tity handled, inlet pressure, and pipe restrictions like bends, valves a^d other fillings. Short runs with few bends and fittings have low pressure loss. Feeding air outlets radially from a compressor in the department aren per mits sizing pipe for oir quantity needed at the outlets. Pipe con bo run and compressor located so there's minimum pressure loss. Tools ond other oiroperated equipment perforin better with Jess power waste, pressure drop being power loss. Less Engineering. With load-center equipment, foctory^ngineered packages serve as substations. All that Is needed Is e flat mounting surface, ond leads to and from substation. Likewise, in unit system for air dis 3 CENTRAL-DISTRIBUTION system hos one or more big oir compressors to supply air through a loop moln ihor runs to oil deportments. Main is largo, Hos long run tribution, most compressor builders can now supply uoits from fractional to 150 hp. Relatively little engineering and planning aro needed for installation. Among tho items not needed for unit systems ore specially built compressor rooms with Inlet ducts and filters, costly foundations to bedrock to cut vibra tion, eitonsive electrical systems, special water pumps and coolers. Solsctlon. To pick a packaged unit all yop need do is figure compressor ca pacity required and then find s suitable unit in the manufacturer's catalog. When It arrives compressor is grouted and bolted tn present plant floor. When motor, receiver and other equip ment are on hand, only the bare cuntpressor is purchased. If no equipment is on hand the complete Installation including motor starter, aflercooler and moisture separator may be purchased. Package Includes all necessary parts, hooked up and mounted on o common base ond ready to be connected to oir and eieciric lines, Fig. I. Maintenance crew cosily installs unit, saving money. If, ot o later date, you over want to niovo packaged compressors, this is cosy, Fig. 2. Lift trucks or other meleriols-handling equipment transport compressor. Purchasing Pacts. With distributors throughout the world handling packaged Electrical-Distribution Systems Closely Resemble Those (or Compressed Air 5 OLD-TYPE electrical distribution system -has b slnglo C NEW-TVPB electrical distribution system uses load-center substation with tong secondary feeders. The cost is high packaged transformers, hos short run lengths, low costs 70 ENGIMEEtINO AND MANAGEMENT SECTION POWEI An excellent oxample of this occurred during World War il. Starting with only a bank ol machine tools and ona 105-cfm compressor early In tho war, nn alrerafl-psris manufacturer saw his load grow to where he needed seven teen 105-cfm compressors. After tho war when business slacked off he shut down lections of his plant in the samo way he had increased their capacity. When his business was almost complete ly gone, and while looking tor other items to produce, he sold most of his machine tools and compressors. TOo latter sold quickly because moving them to another plant was extremely easy. Had tbia manufacturer tried to install a single compressor at the start to lake care of his maximum needs, he might not hove been able to finance U. Also, he'd have a white elephant on his hands when business slacked. This is not on isolated case; oilier manufacturers use the some plan. Think of unit compressors as "build units, you can quickly and easily obtain units from fractional through 150 hp. Where you must increase compressor capacity in a hurry, you can find one of these units fn a matter of hours, In stead of months needed for custom-built jobs. And.the price quoted is what you pay, etcept for (he small additional coal of grout and piping. Financing. Load centers for electrical distribution grow.with the plant, more units being added as demand increases. Ths same is true of unit system for air distribution. Many older plants outgrow their orig ins! compressor installation. To ex pand: (1) A larger centrally located compressor may bo ordered. (2) Other lorge-capacity units may be installed with existing units. (3) Or package units may be scattered in areas needing mure air. Moat plants now choose method 3 for reasons we've alresdy given. Another important reoson for using pocknge units is that it.is easier to sell plant management on small expendi tures for pockoge compressors than on complete replacement or capacity suf ficient to handlo unknown future growth. It's more sensible, from a man agement standpoint to odd needed eapocity in small segments thon to add targe 'capacity for some future dream. ing blocks" added to plant ss air needs increase. This avoids investment (or compressors larger than needed at the moment. Salvage Value. Electrical-equipment manufacturers rcalixed the importance of equipment that could be used over again when introducing load-center sys tems. High salvago value is important where plant expansion or contraction is easily affected by war, business cycles, market changes, inflation, etc. ' Unit system of air distribution has same high salvage value. This is both outside the plant, as with the aircraftparts manufacturer, and within the plant where demands may change. Inside a plant you can easily shift a compressor from one department to another at low cost. Frequently, portable compressors Compartson ol Unit and Central Distribution Systems may be used to supplement Installed capacity during peak loads. .. -- i Unit System - Compmiari1 Tvs 313-ctm stationery Ons 210-cfm stationery Om 103-cfm itoHesary Oss 103-cfm portable founrfel/oni Total for all stationery units listed ebevs Erection Total for oil stationary anils listed above tying LI*, meins end 1 -In foeders $12,476 3,840 24 3470 100 240 600 , Centro! System-- Compressor' One 1061-cfm stationery $10,672 Founds (ion 15 cu yd @ $65.00 per yd oscaroled, formed, poured 975 fraction 10 days* srork for four men @ $30 per day per man 1,200 fta'np 6- and 4-ie. moins with l-ln. feeders 6,000 Portable* have become en important part of unit systems in many plants. They prevent maintenance crews from "robbing" air from production tines while doing work during the day. Port able close to job eliminates costly pip ing or hose runs, doesn't affect shop-fino or maintenance-tool pressure. Htesc compressors have soved many engineers e costly shutdown. In some plants, banks of portables have been rented to keep a shop going while repairs wero made to a large central-system compres sor. Portables are now available as sellpropelled (tractor-compressor) units Total $23,15$ Total $27,047 that provide maintenance department 'iaclodss compressor, motor, oflercoolsr, moithire teporotor, traps, air receiver, motor with an air compressor snd tractor. A ttortsr and eir.roceiver fittings for cocb installation. few of the devices you can hook to trac 'Includes comprottor, synchronous motor, eicitcr, motor-generotor for teller, motor startnr, tor include snowplows, winches, booms, oftcrcooler, molitoro separator, trap, oir receiver ond fittings. (Continued on page 210) fANUAlT Mi EHOINEEEINO AND MANAGEMENT SECTION 77