Document evOJ8n9DG27ryJLGv08BGXeEE

PLANT PROBLEMS the other guy cure his headaches , TYLER HICKS, Associate Editor What Causes Tail-Pipe Water Hammer? HERE ARE T1IE FACTS? We iniUllad o stenm-jet refrigeration system with baromeirie condenser, filled with secondary ejector and Inler-eondonser, and a third-stage dry ejector. After (tart-up, there wn a diiliatt, loud water hammer In tall pipe near 90-deg bate ell. It wasn't heard when condenser vacuum was leas than 27.6 in. lie. nor when steam ejectors were turned olT and condensing water flowed through' tall pipe alone. Exeept for this water hammer, system operation woi fine. We need 29.75 In. Hg to get chilled-water' outlet temperature of 40 F. We eouldn't get it without accepting the hammer, changing steam jet to get higher compression,ratio, moving installation ao tall pipe Is vertical, or changing the 90-deg ells to form a slight angled flow at hotwell bottom. All solutions seem too expensive exeept the water-hommer acceptance. Test vent, to draw air out of tall pipe, didn't work. Increasing toil-plpa vent from 2 to 6 In. did no good.--EM, dag Power to** m&i Here Are the Answers. S/eam mitt. Condensing-mottr Mu -- * t!Corns LIMIT velocity of hot water in the tail pipe to 5-8 ft per sec. This reduces the possibility of water hammer. Facts EM gives indicate that high fluid velocity causes the hammering because condensing-water flow increases as condenser vacuum doc* Use the well-known -impulse-momen tum theory to analyze conditions in the tail pipe- Most hooks on mechanics out line (he procedure (o be used when solving problems of this general typo. If computed velocity whin vacuum is TWO CAUSES of hammer that EM should investigate ore (!) air leaks in the leg or tail pipe (2) tail pipe too short lor the vacuum in the system. Carefully check tail pipe for leaks at fittings, joints, and in the pipe itself. Small leaks are difficult to track down but can eausa severe water hammer. Pin holes in the pipe may be especially 29.75 in. Hg exceeds 10 ft per sec, in crease pipe and fitting size to reduce velocity to a range of 5-8 ft per sec. Use gradual pipe-size reductions and avoid sudden changes in the direction of fluid flow. Sketch shows how 45-deg elbows can be substituted for 90-deg- H B Wayne Brooklyn, N. Y. HOT WATER contacting cold . metal, steam mixing with cold water or eon* tooting cold metal cause E/IP* trouble. If water slugs from the inter-condenser or the condenser alternately floods and runs dry, water hammer will be set UP- Try drilling a hole-in the elbow into which e plug baffle can be screwed. Hole should be or % in. diameter with provision for adjusting baffle set ting. Set baffle at different angtea and listen for water hammer. H hammer etope, fasten baffle permanently In the condenaer tail pipe. C C Howartrr E. Peoria* HI, troublesome on jobs of this type. Cheek the distance from the bottom of the barometric condenser to the low est level of water in hotwell. In my. opinion, at least six to -eight feet of additional piping should be attached to the minimum length required for the vacuum to be carried. Fred A Doenatt, Fori Worth. Texas IN OUR PLANT we had a similar instsl-'; lation, as sketch shows. .Our first itep'-r, to cure water hammer was to replace^ the two lower 90-deg elbows with two-f. 22%-dcg elbow*' When condenim|-.? water temperature was 70 F or less, no water hammer occurred after Otltj change. During the summer, however, conden- sing-water inlet temperature rose to the i 72-75 F range. To maintain our desired ! vacuum in the condenser, 28.4 in. Hg, i condcnsing-wnler flow had to be .io-'; creased. Once again we were plagued with water hammer. Our theory on the cause of the ham mer is based on many observations ol ' this unit in operation. We believe the!** vapor entrained with the cooling water. * causes bubbles In the tall pipe. When 1 these bubbles collapse, water hammer occurs. Now we intend to extend the 6-in. vent _ line down about 30 feet into the tail : pipe. We will cut slots in the vent line < 90 any vapor mixed with the condensing - water in the tail pipe will be drawn Into t the condenser. If this does not cure our hammer, we will raise the water level until it is the Mine height as the horizontal line leav ing the bottom of the condenser. With this hookup there will be no vapor spice in the tail pipe. This will prevent water hammer no matter how much condens ing water is pumped through the unit We'll keep Power readers informed on the outcome of our testa. E E Mots New York, N. Y. for this moth's two new questions from Power readers, turn to page 134 HANT OPESATtON AMD MAINTENANCE SECTION POWEI * Reducing the pressure Increase meant the flow pattern through the elbow must be changed. Steel-tube straightenere, fop sketch, might alter flow pattern to some extent. Splitter vanes in elbow would probably alter pattern more than tube at elbow entrance. Perhaps a com bination of both tubes and vanes would be best. Splitter vanes might also act as baffles to dampen shock waves pro ducing water hammer. Lower sketch shews how an air dome might be used to dampen shock wave* It might be advisable to stiffen the el bow, as shown. H J Wyman Boston, Mass. How Can We Stop Corrosion in Well? HERE ARE THE FACTS; Our cooling systems are,served by several eleepweilt. Seek well has s 44n. pipe that discharges water to our heat exchangers and condenser* Well pressure is.90 pslg with fairly steady How rale. Water temperature Is 58 F. Wbt hookup will control corrosion in both Unci from wells, In heat exchangers and condensers? Is periodic arid cleaning of hcatexehaoge units better than continuous chemical treatment? Which Is belt for a moderate-site Industrial plantT--ST, Aug Power STMT,ROW in a pipe is shut off by a valve, T'Tbe, kinetic energy ol the moving fluid Here Are the Answers.fyit> converted to pressure energy, the -amount of conversion depending on rate valve closure. If valvo closes quickly, jl^yb'ock waves that cause water hammet gj^ipiy be set up. These waves reverse !flow'several times before dying out. To oh comttetser |$'Wt pipe has no valve, and flow ' ^(through it is continuous- Shock waves r/^tbere are caused by the increase in pres- resulting from an abrupt change die fluid's velocity. Since kinetic en- &*er|y varies as the square of the velocity. il&vfrTsmall change in velocity can cause a it* JxoQsIderoble change in kinetic energy. In flow through a bent pipe the veloc- it the inside radius is about one third ir.\piat at the outside radius Normal veloe,- K*riir in the line approaching the elbow l/^jSdecreaees much more rapidly ot the In i' ,ivfPM radius than at the outer. This effect |M1is greater in a 90-deg elbow than in one V:|of 45 dag. -.y/ I think the velocity reduction at tiro l^'fijnnsr radius lends to cause a sizable I'l^.'ypreawre increase that is not quite iufy:;-/'5cient at 27.8-in.-Hg vacuum lo cause hammer. But as vacuum is fn- MOUNT A TANK, as in sketch, and feed treatment chemicals directly into the well. Have a complete analysis mode of the water before choosing treatment chemicals. If pump setup is different from that in sketch, chemicals can be injected at point X. Gr.once Gntrret Bronx, jV. Y. "yrested, water velocity in pipe rises, i&VyeD'r8y conversion increasing as ihe V'-vrQuare of the velocity change. Water , fj hsromer occurs. If my oaaumption is |^;;Mrreci, the hammering increases as vac- CONTINUOUS chemical treatment is best .^am does. - solution for SPa problem. Use a good II this reasoning has some merit, then proportioning pump to feed chemicals f ^,Wo wluiions appear possible (l) lessen- to system. (*the conversion effect (2) domping jjkfcTi hammer after it occurs. Henry Rasmussen Crystal Lake, III- WELL SPECIALIST will save ST plenty of headaches and money. See Power, Au gust 1951, for two excellent articles on wells end their care. D L Cochrans Milica, Mian. (Continued on page 132) j^SfjKOVEMK* Mg) PUNT OPERATION AN0 MAINTENANCE SECTION