【优质】01DefinitionAndUsesOfCompressionPacking

1、Defin iti on And Uses Of Comp ressi on P ack ingCon trol of fluid loss is esse ntial to the successful op erati on of mecha ni cal equ ipment used in fluid han dli ng. Various methods are utilized to con trol leakage at shafts, rods, or valve stems and other fun cti onal p arts or equ ipment requiri

2、 ng containment of liquids or gases.The oldest and still most com mon of these seali ng devices is comp ressi on p ack ing.so called because of the manner in which it p erforms the seali ng fun cti on. Made from relatively soft, p lia nt materials, comp ressi on or jam p ack ings con sist of a n umb

3、er of rings which are in serted into the ann ular sp ace (stuffi ng box) betwee n the rotat ing member, and the body of the pump or valve. By tighte ning a gla nd follower aga inst the top ring, pr essure is tra nsmitted to the p ack ing set, expanding the rings radially aga inst the side of the stu

4、ffi ng box and rotati ng member, effect ing a seal.Typ ical stuffi ng box, cross secti onA. p ack ingB. throatC. stuffi ng box areaD. gla nd stud-bolts and n utsF. later n ring (seal cage)Comp ressi on p ack ing finds its major use in the p rocess in dustries such as p etro-chemical, paper and steel

5、 mills, and in the service in dustries like utilities, mari ne, water, sewage, food and n uclear. They seal all types of fluids in clud ing water, steam, acids, caustics, solve nts, gases, oil, gasoli ne, and other chemicals over a broad range of temp erature and p ressure con diti ons. They are use

6、d in cen trifugal, rotary, and recip rocati ng pumps, valves, expansion join ts, soot blowers, and many other types of mecha ni cal equi pment.Comp ressi on p ack ing is relatively easy to in stall and mai ntain. With proper atte nti on, a high degree of successful op erati on can be an tic ip ated.

7、Successful sealing with compression packing is a function of several important related factors:1) Careful selection of packing material to meet the specific application requirements.2) Complete consideration of surface speeds, pressures, temperatures, and medium handled.3) Proper attention to good i

8、nstallation and break-in procedures.4) High standards of equipment maintenance.How CompressionPacking WorksCompression packing used in pumps, whether in rotating or reciprocating service, normally depends on a fluid film between the surface of the moving member of the equipment, and the packing, for

9、 lubrication. sources of this fluid film are built-in lubricants (liquid, solid, or in combination), leakage of the medium handled, or an external lubricant supply.On equipment start-up, lubricants may be released from the packing by gland pressure to provide initial lubrication and sealing. During

10、the break-in period, these lubricants bridge the period between dry operation and the introduction of the normal lubricating system.Gradually, by adjustment of the gland pressure, the pumped medium, or the external lubricating source, takes over the lubricating function by providing a continuous sou

11、rce of fluid film. Gland pressure is regulated to provide optimum lubrication to seal and prevent overheating and consequent damage to the shaft or rod. Built-in lubricants that are lost gradually during the operation of the equipment are compensated for by further gland adjustment. When the volume

12、loss of lubricated packing approximates the original amount of built-in lubricant, the effectiveness of the packing is lost, and replacement is required. Built-in lubricants may also serve the important function of controlling the passage of fluids being pumped, thus preventing excessive leakage.Com

13、pression packing used in valved where there is slow or infrequent motion, or in static operations, is required to seal without leakage. Various impregnants may be used to assist in this function. Some packing is designed with non-migrating stable lubricants for operation under extreme pressure and t

14、emperature.三凶 11IT I kZ_JTyp ical stuffi ng box with pump sucti on pr essure above atmos pheric p ressure, cross secti onA. po sitive fluid p ressure above atmos pheric pr essureB. atmos pheric p ressureC. leakageAXressure above atmos phericleakage into pump小Typ ical stuffi ng box with pump sucti on

15、 pr essure, cross secti onA. pump sucti on un der vacuum,B. fluid inlet conn ected to pump dischargeC. atmos pheric p ressureD. leakage,leakage into pumpexter nal sourceTyp ical stuffi ng box with pump pumping slurries, cross secti onA. pump sucti on un der vacuumB. fluid inlet conn ected toC. atmos

16、 pheric p ressureD. leakageAno ther typ ical stuffi ng box withpump pumping slurries, cross secti onleakage into pumpexter nal sourceA. pump sucti on un der vacuum,B. fluid inlet conn ected toC. atmos pheric p ressureD. leakageTypes of Con structi onComp ressi on p ack ing is made in a variety of sh

17、a pes, sizes and con structi ons, from various materials. The followi ng is a descri pti on of basic con structi ons which are com monly used, and the virtues of each:Cen terlock?Yar ns, rov in gs, ribb ons, and other forms of various material, either alone or in comb in ati on, are p rocessed on eq

18、u ipment where the stra nds criss-cross from the surface diago nally through the body of the p ack ing. Each stra nd is str on gly locked by other stra nds to form a solid in tegral structure that cannot easily un ravel or come ap art in service. There are no jackets to wear through, and no plaits t

19、o come lose.Cen terlock? p ack ing has a more eve n distributi on of yarn den sity throughout and has the poten tial for imp roved lubrica nt rete nti on. The fini shed p ack ing is relatively den se, but flexible. Cen terlock? p ack ing is suitable for app licati ons on both recipr ocat ing and cen

20、 trifugal pumps, agitators, valves, expansion join ts, and in grooves. Cen terlock? con structi on is also known as "Cross-Locked," "I nter-Lock," "In terlocki ng," "Lattice," "Multi-Lok," etc. Ce nterlock? con struction offers versatile and ada ptab

21、le p ack ing that delivers outsta nding p erforma nee in gen eral service formost plants.Cen terlock?P laitedAlso known as braided or square p laited braid. Yar ns, rov in gs, ribb ons, and other various materials, either alone or in comb in ati on, are p rocessed on equ ipment where stra nds p ass

22、over and un der stra nds running in the same directi on. Result ing p ack ings are usually supp lied in square cross-secti on, but recta ngular sizes can also be braided by this method. The p ack ing is usually soft and can carry a large p erce ntage of lubrica nt. Pl aited p ack ing is easy on equi

23、 pment and is gen erally used for cen trifugal or rotary service at relatively low pr essure. The p ack ing softn ess makes it usable on old or worn equi pment.P laitedBraid Over CoreThe fini shed pr oduct is pr oduced by braid ing one or more jackets of yarns, rov ings, ribb ons, or other forms of

24、various materials over a core, which may be extruded, twisted, wra pped or kni tted. This con structi on allows for a wide range of den sities.83Braid over CoreTwistedYar ns, rov in gs, ribb ons and other forms of various material are twisted together or arou nd a core to obtain the desired size. Wh

25、en metallic material is used in the p ack in g, it can be made to resist high temp eratures and p ressures to resist the pen etrati on of fluids, and to conform to the irregularities of worn equi pment.TwistedWrapp ed. RolledAnd FoldedStri ps of various material (lead, copper, alum in um, rubberized

26、 wove n fabrics, etc.) are made either sp irally wrapp ed, rolled, or folded upon themselves or arou nd a resilie nt or comp ressible core. The rubberized fabric types are stro ng, dense, resilie nt, and are resista nt to the pen etrati on of fluids. The metallic types can alsobe made to resist the

27、pen etrati on of fluids, and can conform to the irregularities ofworn equi pment.foToYoYoOlCIOIC'O IO f O I oTwisted and Cale nderedPl aited and WrappedHow To In stall Pack ingP ack ing The Pump CorrectlyThe importance of packing the pump correctly cannot be overemphasized.Many packing failures

28、are due to incorrect installation of the packing. The following steps have been devised to ensure effective installation of packing on pumps:1. REMOVE ALL THE OLD PACKING FROM THE STUFFING BOX. Clean box and shaft thoroughly and examine shaft or sleeve for wear or scoring. Replace shaft or sleeve if

29、 wear is excessive.2. USE THE CORRECT CROSS-SECTION OF PACKING OR DIE-FORMED RINGS. To determine the correct packing size, measure the diameter of the shaft (inside the stuffing box area if possible) and then measure the diameter of the stuffing box (to give the O.D. of the ring). Subtract the I.D.

30、measurement from the O.D.measure-ment and divide by two. The result is the required size.Cut.Don't Wind3. WHEN USING COIL OR SPIRAL PACKING, ALWAYS CUT THE PACKING INTOSEPARATE RINGS. Never wind a coil of packing into a stuffing box. Rings can be cut with butt (square), bias or diagonal joints,

31、depending on the con- struction. It is recommended that Centerlock? packing be cut only by butt (square) method. The following illustr- ations show these methods of preparing bulk packing. The best way to cut packing rings is to cut them on a mandrel with the same diameter as the shaft in the stuffi

32、ng box area. If there is not shaft wear, rings can be cut on the shaft outside the stuffing box.Hold the packing tightly on the mandrel, but do not stretch excessively. Cut the ring and insert it into the stuffing box, making certain it fits the packing space properly.Each additional ring can be cut

33、 in the same manner, or the first ring can be used as a master from which the balance of the rings are cut.Butt joi ntSkive joi ntIf the butt cut rings are cut on a flat surface, be certa in that the side of the master rin gs, and not the O.D. or I.D. surface, is laid on the rings to be cut. This is

34、 n ecessary so that the end of the rings can be rep roduced.When cutt ing diago nal join ts, use a maple mitre board so that each successive ring can be cut at the correct an gle.It is n ecessary that the rings be cut to the correct size. Otherwise, service life is reduced. This is where die-cut rin

35、gs are of great adva ntage, as they give you the exact ring size for the I.D. of the shaft and the O.D. of the stuffi ng box. There is no waste due to in correctly cut rings.4. INSTALL ONE RING AT A TIME. Make sure it is clea n, and has n ot p icked up any dirt in han dli ng. If desired, lubricate t

36、he shaft in side of the stuffi ng box.Seat rings firmly (exce pt P TFE filame nt and Grap hite yarn p ack ing, which should beoap art. Eachsn ugged up very gen tly, the n tighte ned gradually after the pump is on stream).Joints of successive rings should be staggered and kept at least 90 in dividual

37、 ring should be firmly seated with a tamping tool. When en ough rings have bee n in dividually seated so that the nose of the gla nd will reach them, in dividual tamping should be supp leme nted by the gla nd.5. AFTER THE LAST RING IS INSTALLED, take up bolts fin ger tight or slightly sn ugged up. D

38、o not jam the p ack ing into pl ace by excessive gla nd load ing. Start pump, and take up bolts un til leakage is decreased to a tolerable mini mum. Make sure gla nd bolts are taken up eve nly. STOPPING LEAKAGE ENTIRELY AT THIS POINTWILL CAUSE THE P ACKING TO BURN UP.6. ALLOW PACKING TO LEAK FREELY

39、WHEN STARTING UP A NEWLY P ACKED PUMP.Excessive leakage duri ng the first hour of op erati on will result in a better p ack ing job over a lon ger p eriod of time. Take up gradually on the gla nd as the p ack ing seats, un til leakage is reduced to a tolerable level.Never Try To Stop Leakage En tire

40、ly, Un less We In dicate It Is Safe To Do So7. WHEN SP ECIFIED BY THE PUMP MANUFACTURER, P ROVIDE MEANS OFLUBRICATING THE SHAFT AND PACKING THROUGH THE LANTERN RING BYSUPP LYING WATER, OIL, GREASE OR LIQUID HANDLED IN THE PUMP. Fitti ngs for this purpose are sta ndard on many pumps.Typ ical stuffi n

41、g box with lantern ring, cross secti on8. IF THE STUFFING BOX HAS A LANTERN RING (SEE ILLUSTRATION ABOVE), make sure that the lantern ring, as in stalled, is slightly beh ind the fluid inlet so that it will move un der the in let as follower pr essure is app lied.9. REP LACE PACKING WHEN LEAKAGE CAN

42、NOT BE CONTROLLED BY FURTHERTAKE UP ON THE FOLLOWER GLAND.10. ON CENTRIFUGAL, ROTARY AND REC IP ROCATING PUMPS, about 80% of wear is on the outer two p ack ing rings n earest the gla nd. However, each additi onal ring does throttle some fluid p ressure. On most machi nes, there must be en ough rings

43、 so if one fails, ano ther does the seali ng, and the machi ne n eed not be shut dow n.prawunPRIWear / pr essure load curveThe mecha ni cal pr essure curve above shows eight p ack ing rin gs. The first five rings do the majority of the seali ng. The bottom three do little seali ng, but are n eeded t

44、o fill the available sp ace. The adva ntage of using fewer rings is less rod wear. Also, the stuffi ng box desig n is simp ler and takes less material. But, wear isn't the only pr oblem. With high temp eratures, high pr essures, corrosive chemicals, or abrasive p articles in the fluid, more ring

45、s may be the only soluti on for some services. In such cases, the bottom ring con tact ing the fluid may have the most wear from these severe service con diti ons.P ack ing Valves CorrectlyAs with pump p ack ing, the first ste p in gett ing the most out of a valve p ack ing is correct in stallati on

46、. Here is the correct way to p ack valves.1. CAREFULLY P ERFORM ALL OP ERA- TIONS LISTED UNDER PUMP P ACKING, STE PS 1-5. Rings used on valves and expansion joints are gen erally cut with a diago naljoin t (illustrated below). I n preparing diag onal cut (45o)rin gs, be sure that the firstring is cu

47、t carefully and the n tested on the stem.Skive joi nt2. BRING THE FOLLOWER DOWN ON THE PACKING TO THE POINT WHERE HEAVYRESISTANCE TO WRENCHING IS FELT. During this time, turn valve stem back and forth to determine ease of turning. Do not torque down to the point where the stem won't turn.3. AFTE

48、R THE VALVE HAS BEEN ON THE LINE A DAY OR SO, EVEN IF NO LEAKAGEEXISTS, THE FOLLOWER SHOULD BE TIGHTENED SLIGHTLY. Obviously if leakage is occurring, the follower must be tightened.Trouble-Shooting Packing FailuresPacking may fail for a variety of reasons. Beside improper installation, packing failu

49、res are often due to worn or faulty equipment, shaft misalignment, uneven take-up on the gland bolts, and other causes.If you are having trouble, carefully remove and examine the old packing set. DONOT THROW THE SET AWAY, because it often gives clues as to the condition of the equipment, and may be the means of solving the problem. The following clues and possible causes were found by examining sets of packing which failed in service.CLUEExcessive redu