POWER EQUIPMENT INSTRUCTOR: ROBERT A. MCLAUGHLIN ZAILI THEO ZHAO 10:06 POWER EQUIPMENT INSTRUCTOR: ROBERT A. MCLAUGHLIN ZAILI THEO ZHAO SHAFT SEALS, MECHANICAL SEALS & COMPRESSION PACKING

Learning Objectives 10:06 The 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.

Compression Packing 10:06  Packing is used to seal shafts, rods, or valve stem seals. Packing materials will vary with the substance being sealed, like Steam Acids Caustics Solvents Petroleum products The difference between valve stem and shaft packing. Shaft seal has leakage and valve stem not Shaft is rotating at high speed and valve stem not.

Compression Packing 10:06 A 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.

Compression Packing 10:06 Packing 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.

Packing maintain Packing is easy to maintain. 10:06 Packing is easy to maintain. Important considerations when installing to insure long packing life: Use the correct packing for the application. Use the correct material Use the correct size To 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.

Packing maintain Know environment such as 10:06 Know environment such as Surface speed of shafts The softer the packing the greater the shaft speed it can take. Fluid pressure Fluid temperatures Material that is being sealed, such as acids or caustics The table shows the permissible surface speed and RPM for various sealing materials and shaft diameters, in the case of non-pressure conditions.

Packing maintain 10:06 Proper equipment maintenance such as insuring shaft sleeve is in good condition. Proper installation of packing and lantern rings.

Packing maintain Allow for packing break in. 10:06 Allow 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.

Lantern ring (3-L-2) 10:06 Because 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.

Packing size The following sizes of braided packing are available: 10:06 The following sizes of braided packing are available: Inch sizes 1/8", 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 sizes 3.2mm, 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, 38.1mm Shaft and packing size 5/8″ to 1 1/8″ shaft 5/16 ″ packing width 1 1/8 ″ to 1 7/8 ″ 3/8 ″ packing 1 7/8 ″ to 3 ″ ½ ″ Packing 3 ″ to 4 ¾ ″ 5/8 ″ packing 4 ¾ ″ to 12 ″ ¾ ″ Packing

Packing cuts and installation 10:06 Butt cut – ends are square Skive – ends are cut at 45o angle Installation Two rings – stagger ends 180o apart Three rings – stagger ends 120o apart Four rings – stagger ends 90o apart NOTE: USCG says that regardless of the number of rings of packing, then should be 180o apart.

TYPES OF CONSTRUCTION Braided – braided square braid 10:06 Braided – braided square braid The individual strands pass over and under each other to form a square Braid – over – braid Same as above but results in a round packing Braid – over – core Braided pattern with a center core Core is often material added for strength. Thick nylon string Some have metal cores Interbraid – 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.

Common packing material 10:06 Natural fibers Asbestos – health hazard Good for high temperature applications Will sometimes have wire inserted into the packing for strength. Man – made fibers Acrylic fibers – fiber glass like material that is spun into strands – then interbraided into packing. Good chemical resistance Glass Fibers woven into packing. Excellent for high temperature applications PTFE – Teflon base Excellent chemical Limited temperature application. Aramid Fibers – know for its high strength, suitable for high pressure, and temperatures up the 500oF

Common packing Lubricants 10:06 Packing 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 lubricants Graphite Teflon

FITTING 10:06 Remove 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

FITTING 10:06 Measure 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.

FITTING 10:06 Slight 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.

FITTING 10:06 If 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.

Keystone effect 10:06 When 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.

Mechanical Seals 10:06 One 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").

Mechanical Seals 10:06 One 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 = .000011″

1) Rotating seal ring, 2) stationary seal ring 10:06 1) Rotating seal ring, 2) stationary seal ring 3a) Rotating secondary seal, 3b) Stationary secondary seal, 4) Spring, 5a) Upper drive pin, 5b) Lower drive pin

REASONS FOR USING MECHANICAL SEALS 10:06 No leakage Reduced power consumption Reduced labor costs Less down time Positive sealing for toxic products Dollar savings with no product loss

TYPES OF SEAL-INSIDE SEAL 10:06 Mounted inside the stuffing box of the pump. This is the most popular location for pump seals Advantages Easy 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

TYPES OF SEAL-OUTSIDE SEALS 10:06 Located outside the stuffing box. Easy to install The 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.

MECHANICAL SEALS - TYPES OF SEAL 10:06 Beyond inside or outside, seals are also classed as: Single seals Double Seals Tandem seals

COMPONENT SEALS 10:06 Older 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 clean The spring tension must be set according to the manufactures recommendations.

CARTRIDGE SEALS Newer seals are they are: Easy to install 10:06 Newer seals are preassembled as a unit. already adjusted for you. they are: Easy to install Less chance of face contamination.

Mechanical Seals – “O” Rings 10:06 The 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.

Mechanical Seals 10:06 Seal materials will vary with the operating pressures, temperature, and the type of material being pumped.

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Mechanical Seals 10:06 The 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.

LABYRINTH SEALS – HOW DOES IT WORK 10:06 A seal with no direct contact Seals that do not touch the shaft Three factors that determine the effectiveness Number of teeth in seal – more is good. Condition of teeth – sharp is good. Length of teeth – longer is good.

Labyrinth seals - used on centrifugal compressor 10:06 Non contacting isolated air and oil seals ; life long operation and 100% oil free air

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