Presentation on theme: "POWER EQUIPMENT INSTRUCTOR: ROBERT A. MCLAUGHLIN ZAILI THEO ZHAO"— Presentation transcript:
1POWER EQUIPMENT INSTRUCTOR: ROBERT A. MCLAUGHLIN ZAILI THEO ZHAO 10:06POWER EQUIPMENT INSTRUCTOR: ROBERT A. MCLAUGHLIN ZAILI THEO ZHAOSHAFT SEALS, MECHANICAL SEALS & COMPRESSION PACKING
2Learning Objectives10:06The various types of material used in compression type packing.The proper shaft sealing and how to measure and correctly cut packing.The proper method of removal and installing compression packing in a pump.What a mechanical seal consists of and how it differs from compression packing.A single mechanical seal and a double mechanical seal.The advantages of the use of mechanical seals over compression packing in a pump.The difference between the component seal and the cartridge seal assembly.Labyrinth seals in steam turbine.
3Compression Packing10:06 Packing is used to seal shafts, rods, or valve stem seals.Packing materials will vary with the substance being sealed, likeSteamAcidsCausticsSolventsPetroleum productsThe difference between valve stem and shaft packing.Shaft seal has leakage and valve stem notShaft is rotating at high speed and valve stem not.
4Compression Packing10:06A packing gland is used to press against the top ring which in turn transmits the pressure to through out the packing set, and causing the packing to expand against the stuffing box and the rotating shaft or a stationary valve stem.
5Compression Packing10:06Packing is made from relatively soft, pliant materials which are compressed into an annular space called the stuffing box between a rotation or reciprocating member and the body of the pump or valve.
6Packing maintain Packing is easy to maintain. 10:06Packing is easy to maintain.Important considerations when installing to insure long packing life:Use the correct packing for the application.Use the correct materialUse the correct sizeTo determine correct packing size, measure stuffing box diameter and shaft diameter.Subtract shaft diameter from stuffing box diameter, then divide that by 2, that equals packing size.
7Packing maintain Know environment such as 10:06Know environment such asSurface speed of shaftsThe softer the packing the greater the shaft speed it can take.Fluid pressureFluid temperaturesMaterial that is being sealed, such as acids or causticsThe table shows the permissible surface speed and RPM for various sealing materials and shaft diameters, in the case of non-pressure conditions.
8Packing maintain10:06Proper equipment maintenance such as insuring shaft sleeve is in good condition.Proper installation of packing and lantern rings.
9Packing maintain Allow for packing break in. 10:06Allow for packing break in.Packing used against a turning shaft must have a slight leakage for lubrication and cooling.The packing need to ride of a fluid film, and if it is tightened to quickly, the packing will ride on the shaft sleeve, leading to burning of the packing and abnormal wearing of packing sleeve.For break in period, tighten gland bolts hand tight only.Tighten up on the gland nuts ½ turn at a time, over a long period of time.Packing used in a valve is required to seal without leakage.
10Lantern ring (3-L-2)10:06Because of the speed of the shaft, most pump packing applications need to an external source of lubrication.This is accomplished by introducing high pressure fluid to a lantern ring or seal cage.The lubrication provides a flush seal and lubricating film.Successful sealing reduces friction, flushes abrasion, and cools.
11Packing size The following sizes of braided packing are available: 10:06The following sizes of braided packing are available:Inch sizes1/8", 3/16", 1/4", 5/16", 3/8", 7/16", 1/2",9/16", 5/8", 3/4", 7/8", 1", 1 1/8", 1 1/4", 1 1/2“Metric sizes3.2mm, 4.8mm, 6.4mm, 7.9mm, 9.5mm, 11.1mm,12.7mm, 14.3mm, 15.9mm, 17.5mm, 19.0mm, 20.6mm,22.2mm, 23.8mm, 25.4mm, 28.5mm, 31.7mm, 38.1mmShaft and packing size5/8″ to 1 1/8″ shaft 5/16 ″ packing width1 1/8 ″ to 1 7/8 ″ 3/8 ″ packing1 7/8 ″ to 3 ″ ½ ″ Packing3 ″ to 4 ¾ ″ 5/8 ″ packing4 ¾ ″ to 12 ″ ¾ ″ Packing
12Packing cuts and installation 10:06Butt cut – ends are squareSkive – ends are cut at 45o angleInstallationTwo rings – stagger ends 180o apartThree rings – stagger ends 120o apartFour rings – stagger ends 90o apartNOTE: USCG says that regardless of the number of rings of packing, then should be 180o apart.
13TYPES OF CONSTRUCTION Braided – braided square braid 10:06Braided – braided square braidThe individual strands pass over and under each other to form a squareBraid – over – braidSame as above but results in a round packingBraid – over – coreBraided pattern with a center coreCore is often material added for strength.Thick nylon stringSome have metal coresInterbraid – the packing material strands crisscross diagonally across the depth of the packing.Interbraid packing offers exceptional strength – each strand is solidly interlocked to the others which prevent the packing from easily unraveling.
14Common packing material 10:06Natural fibersAsbestos – health hazardGood for high temperature applicationsWill sometimes have wire inserted into the packing for strength.Man – made fibersAcrylic fibers – fiber glass like material that is spun into strands – then interbraided into packing.Good chemical resistanceGlass Fibers woven into packing.Excellent for high temperature applicationsPTFE – Teflon baseExcellent chemicalLimited temperature application.Aramid Fibers – know for its high strength, suitable for high pressure, and temperatures up the 500oF
15Common packing Lubricants 10:06Packing used for high speed rotating equipment will generally have some sort of lubricant to assist with the break-in periods and to increase the packing life.The entire depth of the packing will be impregnated with the lubricant.This can provides the packing with a resiliency; an ability to resist chemical attack, and the ability to resist breaking down.Lubricants can break down when subjected to high temperatures.Common lubricantsGraphiteTeflon
16FITTING10:06Remove all old turns of packing, clean the stuffing box thoroughly, avoid scratching the shaft. Check for shaft run-out and the condition of the stuffing box. Using the sleeve
17FITTING10:06Measure shaft and stuffing box, to determine the correct size of packing required.The correct size of packing is important, as square braided packings are made in such a way that distortion to another dimension distorts the sealing faces and creates the need for excessive gland pressure to prevent leaks, causing overheating, with it's attendant problems.
18FITTING10:06Slight pressure with a 'rolling pin' action is permissible, to facilitate some packing installation.Packing rings should be cut square around a shaft of the same diameter as the pump being re-packed. A square cut avoids unravelling. Wrapping the packing around the shaft two or three times, then cutting longitudinally along the shaft, will ensure rings of the correct length with neatly fitting ends.
19FITTING10:06If rings are cut while the packing is stretched out straight, the ends will meet at an angle when the ring is placed around the shaft and a gap is created. The rings on either side will then squeeze into this gap, preventing the ring from closing - a common cause of leaks.When placing rings over the shaft, it is preferable to open a ring sideways and not with a spreading action.
20Keystone effect10:06When square shaped packing is wrapped around a shaft of sleeve, the cross sectional shape has a tendency to distort into a keystone or trapezoidal shape.Some packing manufactures make packing counter act this.Also the trend of using smaller rather than larger packing means the keystone effect is not as pronounced.
21Mechanical Seals10:06One of the most effective ways of sealing rotating shafts is with mechanical seals.These consist of two plane faces arranged perpendicular to the axis of the rotating shaft (which gives rise to the alternative name, "radial face seal").
22Mechanical Seals10:06One face is fixed to the equipment casing or vessel, while the other is fixed to the shaft and so rotates with it.Frictional heat generation and wear are controlled by maintaining a very fine film of lubricant between the seal faces.The faces are within two light bands of flatness.1 light band = ″
231) Rotating seal ring, 2) stationary seal ring 10:061) Rotating seal ring, 2) stationary seal ring3a) Rotating secondary seal, 3b) Stationary secondary seal,4) Spring, 5a) Upper drive pin, b) Lower drive pin
24REASONS FOR USING MECHANICAL SEALS 10:06No leakageReduced power consumptionReduced labor costsLess down timePositive sealing for toxic productsDollar savings with no product loss
25TYPES OF SEAL-INSIDE SEAL 10:06Mounted inside the stuffing box of the pump.This is the most popular location for pump sealsAdvantagesEasy to apply cooling fluid – usually through holes in the seal gland flange.Centrifugal action as it spins keeps it clean.Not prone to major leaking
26TYPES OF SEAL-OUTSIDE SEALS 10:06Located outside the stuffing box.Easy to installThe outside of the seal can be made of readily available inexpensive materials because it is not in contact with the pumped fluid.Not easy to cool keep cool, and is more prone to failure.Cannot be used in high pressure situations.
27MECHANICAL SEALS - TYPES OF SEAL 10:06Beyond inside or outside, seals are also classed as:Single sealsDouble SealsTandem seals
28COMPONENT SEALS10:06Older and cheaper seals are what are called component seals– all off the seal parts come separate and must be assembled on the pump on site.To install a component seal:All surfaces must be cleanThe spring tension must be set according to the manufactures recommendations.
29CARTRIDGE SEALS Newer seals are they are: Easy to install 10:06Newer seals arepreassembled as a unit.already adjusted for you.they are:Easy to installLess chance of face contamination.
30Mechanical Seals – “O” Rings 10:06The rotating part of the seal will have a boot or “O” to prevent liquid under pressure from escaping along the shaft.The stationary assemble will have gaskets and/or “O” rings to prevent the liquid from escaping over the sealing faces.
31Mechanical Seals10:06Seal materials will vary with the operating pressures, temperature, and the type of material being pumped.
33Mechanical Seals10:06The seals faces operate with a very thin film of liquid which serves to lubricate and help cool the faces of the seal.Usually enough heat is generated so that the film liquid vaporizes.Cooling fluid is introduced (the fluid being pumped) around the seal faces to flush out solids in the stuffing box and to cool the seal faces.Centrifugal action usually prevents any solids from entering and migrating across seal faces.
34LABYRINTH SEALS – HOW DOES IT WORK 10:06A seal with no direct contactSeals that do not touch the shaftThree factors that determine the effectivenessNumber of teeth in seal – more is good.Condition of teeth – sharp is good.Length of teeth – longer is good.
35Labyrinth seals - used on centrifugal compressor 10:06Non contacting isolated air and oil seals ; life long operation and 100% oil free air