Seal damage


After the seal failure has occurred you will analyze the failed components. You are going to be looking for several things:

  • Evidence of corrosion.
  • Wear patterns on those parts that should be rubbing.
  • Evidence of rubbing or wear on those components that should not be in contact.
  • Discoloration of any of the seal components, especially the metal parts.
  • Parts that are missing. Springs, set screws and drive lugs as an example.
  • Loose hardware. Either a seal component or a foreign object.
  • Product attaching to a rotating component. Carefully inspect the impeller and rotating part of the seal.

In the following paragraphs we will be inspecting the individual components and looking for evidence of the above. But before we get into that subject there are a couple of important points that you must keep in mind as you trouble shoot individual components:

Are you looking at a seal that has been rebuilt? Were the components cleaned before you looked at them? Troubleshooting a rebuilt seal is a frustrating experience. A trained troubleshooter is looking for evidence of rubbing, damage and corrosion. If those previous rubbing marks have not been removed from the rebuilt seal you can be led down a false path.

  • A good rebuilding house would :
    • Clean and polish the seal casing to remove any rub marks. If this was not done you may be trying to analyze a rub mark indication that happened several applications ago, in a different pump.
    • Install a new carbon/ graphite molded face. Machined faces are not acceptable because they do not have the proper density. If the used face had only been relapped, the length of the carbon nosepiece will not be an indication of anticipated life in this application.
    • Replace all the springs. Springs are made from corrosion resistant, austenitic materials that work harden over a period of time. Being a small cross section material that is under high stress, they are also sensitive to chemical attack.
    • Replace the setscrews. They are made from austenitic metal also and should never be re-used.
    • Replace all rubber parts (O-rings, rubber boots, etc.)
    • Solid hard faces can be relapped if there are no significant chips or visible cracks. Plated hard faces should never be relapped.
  • Be sure to identify the seal materials. It is impossible to troubleshoot mystery materials.
    • If the metal is stainless steel, which grade is it? All stainless steels are not the same. There is a difference between Hastelloy C and Hastelloy B. Some people call Alloy 20 stainless steel, but it is a different product.
    • There are a hundred different grades of carbon graphite used in mechanical seals. Which grade are you looking at? Is it filled or unfilled?
    • Viton® is a trade name for E.I.Dupont. There are many grades of this product available. Some work in water, others do not. Which do you have?
    • What is the spring material? It should be Hastelloy C, but is that what you have?


Chipping on the outside diameter of the carbon. Indicating vibration of some type.

  • “Slipstick” can occur if you are pumping a fluid with poor lubricating qualities.
  • Mishandling is a common problem. Look for evidence of drive lug wear to eliminate this as a possibility. Chipping without drive lug wear is a good indication of mishandling.
  • Vaporization of the liquid between the lapped faces causing the faces to rapidly open and then close as the leaking vapor cools the faces.
  • A discharge recirculation line is aimed at the carbon seal face. Each pass of an impeller vane puts a pulse into the recirculation line.
  • The pump is cavitating. Remember there are five types of cavitation.
  • Water hammer is an another possibility.
  • Running at, or passing through a critical speed will cause vibration problems

Pits in the carbon face. This problem is usually associated with poor grades of carbon/ graphite.

  • Exploded carbon. Air trapped in the pores of the carbon expands and expels pieces of the carbon when the seal faces get hot. Prior to ejection polished patches will be visible, usually with small cracks visible in the center.
  • If the product solidifies between the faces it will tear out pieces of the carbon at start up. This is a common occurrence with ammonia compressor seals because petroleum oil is mixed with the ammonia and the oil can coke at the elevated face temperature.
  • Most petroleum products will “coke” because of the higher face temperature, and pull out small pieces of the carbon as the faces rotate. You will see evidence of these small pits if you inspect the carbon face under a magnifying glass. This is one of the main reasons that carbon/ graphite seal faces have trouble passing fugitive emission standards in hot petroleum applications.

Chipping at the inside diameter of the carbon

  • Solids or a foreign object of some type from outside of the pump is getting under the gland and is being thrown into the seal faces. This can occur if the seal leaked at some time and the product solidified on the outboard side of the seal. It can also occur if liquid containing solids is used in the quench connection of an API (American Petroleum Institute) type gland.
  • If the seal was installed outside of the stuffing box, as is the case with non-metallic seals, solid particles in the fluid can be centrifuged into the rotating carbon face.
  • If the stationary face is manufactured from carbon it can be chipped if it comes into contact with the rotating shaft. This is a common problem at pump start up, or if the pump is operating off of its best efficiency point (BEP)
  • Vertical pumps experience this problem when solids fall between the seal and the shaft.

Phonograph finish on the carbon face.

  • A solid product was blown across the seal face. Since one of the faces is rotating the solid particle follows a circular path until it is expelled out of the inside diameter of the lapped faces. This happens frequently in boiler feed water applications.

Chemical attack of the carbon.

  • You are using the wrong grade of carbon/ graphite. Something in the product or the flush is attacking the carbon filler. Switch to an unfilled carbon such as Pure grade 658 RC or C.T.I. grade CNFJ.
  • You are trying to seal an oxidizing agent. Oxidizers attack all forms of carbon including the unfilled type. The carbon combines with the oxygen to form either carbon monoxide or carbon dioxide.
  • You are trying to seal a halogen like chlorine, fluorine , bromine, astintine or iodine.
  • Some forms of de-ionized water will pit and corrode carbon faces

Cracked or damaged carbon face.

  • The product is solidifying between the faces. Carbons are strong in compression but weak in tension or shear. This problem is common with intermittent service or standby pumps each time they start up.
  • Excessive vibration can bang the carbon against a metal drive lug.
  • A cryogenic fluid is freezing a lubricant that was put on the face.
  • The elastomer is swelling up under a carbon face.
  • The shaft is hitting the stationary face or the rotating seal face is hitting a stationary object.
  • Mishandling.
  • Poor packaging. The lapped seal faces should be able to survive a 39″ (one meter) drop.
  • The fluid, containing solids, is underneath the carbon face. Centrifugal force is throwing solids or abrasive material into the soft carbon. You see this problem in dual, back to back, rotating seals and outside mounted non-metallic seals.

A coating or layer of product is forming on the carbon face:

  • Look for a change in temperature in the stuffing box. Many products solidify at temperature extremes, but some solidify or build a film with a minor change in temperature.
  • The product is taking a pressure drop across the seal faces and solidifying as it passes through the lapped faces.
  • The fluid you are pumping has been demineralized or deionized. Selective leaching is picking up one or more missing elements from the piping system and depositing them on the seal face. This accounts for the copper plating you sometimes see on the carbon face in boiler feed pump applications.
  • The stuffing box is running under a vacuum because the impeller was adjusted backwards and the impeller “pump out vanes” are pumping out the stuffing box.
  • Corrosion resistant materials form a protective oxide coating. This protective oxide is depositing at the faces. In cast iron pipe hot water systems we experience this problem with magnetite (Fe3O4) until the system stabilizes.

Coking. The forming of a hard black layer on the seal face. It is difficult to see on carbon, but you might notice that the carbon nosepiece is getting longer.

  • Coking is a problem with all oils, and petroleum products in particular.
  • Coking is caused by the combination of high temperature and time. Contrary to popular belief the presence of air or oxygen is not necessary.

Shiny spots, cracks and raised portions of carbon.

  • The carbon does not have enough density, causing the expanding gases trapped beneath the surface of the carbon to bubble at the face.

Excessive carbon wear in a short period of time. Evidence of excessive heat is usually present.

  • Heat checking of the hard face. It shows up as a cracking of the hard face. This is a problem with coated or plated hard faces. Cobalt base tungsten carbide is a typical example. These cracks will act as knife blades and shave the carbon face. You often find carbon dust underneath the carbon face.
  • The shaft is moving in an axial direction because of thrust. This can cause an over compression and heating of the seal faces. Pumps equipped with sleeve bearings are a bigger problem
  • The impeller is being adjusted towards the back plate. This is problem with seals installed in Duriron pumps or any other pump that adjusts the open impeller against the back plate.
  • A number of installation problems can cause excessive wear of the carbon face:
    • The inner face of a “back to back” double seal application is not positively locked in position. A snap ring must be installed to prevent the inboard stationary face from moving towards the rotating face when the high-pressure barrier fluid pressure is lost or overcome by system pressure.
    • The seal was installed at the wrong dimension. It has too much spring compression
    • A cartridge double seal was installed by pushing on the gland. Friction, between the shaft and the sleeve O-ring is compressing the inner seal.
    • A vertical pump was not vented.
    • You are using an unbalanced seal in a balanced seal application.
  • Solids have penetrated between the lapped faces. Here are some common causes:
    • The faces are not flat or maybe they never were flat
    • The movable face is sluggish. It has trouble following shaft run out.
    • The product is vaporizing between the faces because of either high temperature or low stuffing box pressure.
  • Non lubricants will cause rapid face wear. A non-lubricant is any fluid with a film thickness less than one micron at its operating load and operating temperature.

The carbon has a concave or convex wear pattern

  • High-pressure distortion.
  • The gland holding the stationary seal carbon face is not perpendicular to the shaft. It is causing an uneven loading on the carbon face.
  • Some companies lap a concave pattern as standard. Check with your manufacturer.
  • The shaft is deflecting because the pump is running off of its best efficiency point (BEP)

The carbon is not flat.

  • Mishandling.
  • Poor packaging. The seal should be packaged to survive a one-meter (39 inches) drop without seal component damage.
  • The seal was shipped out of flat.
  • The seal was rebuilt by a facility that cannot check flatness, or the person responsible for doing it does not know how.
  • The metal/ carbon composite has not been stress relieved and it is distorting the carbon.
  • The carbon was shrunk into a metal holder. It should have been pressed in and sheared to conform to irregularities in the holder diameter.
  • When the carbon was lapped, the lapping plate was too hot and not flat.
  • The carbon was lapped at room temperature and the seal is running at cryogenic temperatures.

Solids are imbedded in the carbon.

  • The seal faces opened, letting the solids penetrate between the lapped faces.
  • Some one used lapping powder to lap the carbon face. The carbon should have been lapped dry, on ceramic stones.


Chemical attack.

  • Caustic and other high pH fluids attack some ceramics and silicon carbides. Check to see if your seal face material contains silica. As an example: both reaction bonded silicon carbide and 85% ceramic have this high silica content.

Cracked or broken.

  • The product is solidifying between the faces. Most hard faces have poor tensile or shear strength.
  • Excessive vibration will cause cracking at the drive lug location.
  • A cryogenic fluid is freezing a lubricant that was put on the face.
  • The elastomer is swelling up under an outside seal face. This problem can also occur if the seal design allows a spring to contact the inside diameter of the hard face. You see this design problem in most dual, “back to back”, rotating seal designs
  • The shaft is hitting the stationary face or the rotating seal face is hitting a stationary object. This is a good reason for converting your pump to an oversized stuffing box.
  • Mishandling.
  • Poor packaging.

Heat check (common with coated or plated faces)

  • Heat check or cracking of the hard face is caused by a high heat differential across the face. Most hard coatings have only one-third the expansion rate of the stainless steel base material.

Hard coating coming off the face.

  • The base material not compatible with the sealed product. These coating are very porous so if the product attacks the base material the coating will come off in sheets.
  • The plating process was not applied correctly.
  • High heat can cause a problem with the differential expansion rate between the coating and the base material.

Let’s analyze the wear track on the hard face. We will be looking for deep grooves or excessive wear caused by:

  • Solids imbedded in the carbon are causing the problem.
    • The seal faces opened letting the solids penetrate between the lapped faces. The carbon is softer than the hard face so the solids penetrate into the carbon.
    • Someone used lapping powder to lap the carbon face and the lapping powder is imbedded into the carbon. The carbon should have been lapped dry, on ceramic stones.

The wear track is wider than the carbon. The shaft is having run-out problems

  • Worn bearings.
  • A bent shaft.
  • An unbalanced impeller.
  • The sleeve not concentric with the shaft.
  • The seal not concentric with the sleeve.
  • You are using a pump seal in a motion seal application.
  • In a stationary seal design, the stationary carbon is often not centered to the shaft causing a wiping action.

The graphite wear track is narrower than the carbon.

  • The soft face (carbon) was distorted by pressure.
  • The hard face was over tightened against an uneven surface. It is now either concave or convex.
  • The hard face clamping forces are not “equal and opposite”. You probably have two different width gaskets on either side of a clamped hard face.
  • The face never was flat or it was damaged during shipment.

Non-concentric pattern. The wear track is not in the center of the hard face.

  • The shaft is bending because the pump is running off of its best efficiency point.
  • Poor bearing fit.
  • Pipe strain.
  • Temperature growth is distorting the stuffing box.
  • The stationary face is not centered to the shaft.
  • Misalignment between the pump and its driver.

Uneven face wear. The hard face is distorted:

  • High pressure.
  • Excessive temperature.
  • Over tightening of the stationary face against the stuffing box.
  • The clamping forces are not equal and opposite.
  • The hard face is not wide enough. It needs more mass to resist the clamping forces.
  • You are using a two-bolt gland, and the gland is too thin causing it to distort the stationay face.

The product is sticking to the seal face. The product is changing state and becoming a solid. Most products solidify for the following reasons:

  • A change in temperature.
  • A change in pressure.
  • Dilatants will solidify with agitation. As an example: cream becomes butter.
  • Some products solidify when two or more chemicals are mixed together. Like epoxy glue.

The hard face is not flat.

  • Mishandling. Parts get dropped and the worker is afraid to tell the boss. He put the part back in inventory without telling any one what happened.
  • Poor packaging.
  • The hard face has been installed backwards and you are running on a non-lapped surface.
  • It was shipped “out of flat.”


Compression set. The elastomer has changed shape. It started off round, but now the O-ring is almost square.

  • High heat is almost always the cause unless you are dealing with Kalrez® , Chemraz, or a similar Perfluroelastomer where a certain amount of compression set is normal because these materials are not true elastomers.

Shrinking, hardening or cracking.

  • High heat is the main cause of this one. First you get the compression set and then comes the hardening, cracking etc.
  • The shelf life was exceeded. This is a big problem with “buna N” that has a shelf life of only twelve months.
  • Cryogenics will freeze just about any elastomer.
  • Chemical attack normally causes swelling, but in rare cases can harden an elastomer.
  • Oxidizing liquids can attack the carbon that is used to color most elastomers black.

Torn nibbled, or extruded.

  • Mishandling.
  • Sliding over a rough surface.
  • The O-ring is being forced out of the O-ring groove by high pressure. The elastomer will then extrude into sliding components of the seal. The solution to this extrusion problem is to go to a back up ring.
  • The liquid has penetrated the elastomer, vaporized inside and blowing out pieces. This can happen with ethylene oxide.
  • Halogenated fluids can penetrate the Teflon® coating on an elastomer and cause the base material to swell up, splitting the Teflon® jacket or coating. The new perfluroelastomers have made dynamic, jacketed and coated O-rings obsolete.

Swelling, changing color, weight or size. This is almost always caused by chemical attack.

  • Be careful of the lubricant used to install the elastomer. A petroleum product such as grease or oil can attack ethylene propylene rubber.
  • Solvents or cleaners used in the system may not be compatible with the elastomer.
  • Some compounds are sensitive to steam. Most grades of Viton® are a good example of this problem.
  • The elastomer is not compatible with something in the fluid you are sealing.

Torn rubber bellows.

  • The bellows did not vulcanize to the shaft because you used the wrong lubricant during installation. The proper lubricant would attack the bellows and cause it to swell up so that it would stick to the shaft.
  • If the shaft is too smooth the rubber bellows will not stick. The shaft finish should be no better than 40 rms.
  • The shelf life of the rubber material was exceeded.
  • The seal faces stuck together and the shaft spun inside the bellows.
  • The pump discharge recirculation line was aimed at the rubber bellows. Solids entrained in the high velocity liquid are abrading the bellows material.


Corrosion is the main problem. Here are some types of corrosion we find with stainless steel components. You will find details about these different corrosions in the alphabetical section of this book

  • General or overall. This is the easiest to see and predict. The metal has a “sponge like” appearance. Overall corrosion always increases with an increase in temperature.
  • Concentrated cell or crevice corrosion. Caused by a difference in concentration of ions, or oxygen in stagnant areas causing an electric current to flow. Common around gaskets, set screws, threads, and small crevices.
  • Pitting corrosion. Found in other than stagnant areas. Extremely localized. Chlorides are a common cause. Can be recognized by pits and holes in the metal.
  • Stress corrosion cracking. Threshold values are not known. A combination of chloride, tensile stress, and heat are necessary. Chloride stress corrosion is a serious problem with the 300 series of stainless steels used in industry. This is the reason you should never use stainless steel springs or stainless metal bellows in mechanical seals.
  • Inter granular corrosion. Forms at the grain boundaries. Occurs in stainless steel at 800-1600 F. (412-825 C.), unless the part has been stress relieved. A common problem with welded pieces. Stabilizers such as columbium are added to the stainless steel to prevent this. Rapid cooling of the welds, the use of 316L and stress relieving after the welding are the common solutions.
  • Galvanic corrosion. Occurs with dissimilar materials in physical contact, in a liquid and connected by an electrical current. Common in brine, caustic, and salt water applications.
  • Erosion / Corrosion. An accelerated attack caused by a combination of corrosion and mechanical wear. Vaporization, liquid turbulence, vane passing syndrome, and suction recirculation are special cases often called cavitation. Solids in the liquid and high velocity increase the problem.
  • Selective leaching. Involves the removal of one or more elements from an alloy. Common with demineralized or deionized water applications.
  • Microorganisms, that will attack the carbon in active stainless steel.

Rubbing all around the metal body.

  • A gasket or fitting is protruding into the stuffing box and rubbing against the seal.
  • The pump discharge recirculation line is aimed at the seal body.
  • The shaft is bending due to the pump operating off of its best efficiency point.
  • Pipe strain.
  • Misalignment between the pump and its driver.
  • A bolted on stuffing box has slipped and the stuffing box inside diameter is contacting the rotating seal outside diameter.
  • Thermal growth of the pump wet end.

Partial rubbing on the metal body.

  • Bent shaft.
  • An unbalanced impeller or rotating assembly.
  • Excessively worn or damaged by corrosion or solids in the product.
    • The product has attached its self to the impeller.
    • The impeller never was balanced.
    • The impeller was trimmed, and not re balanced.
  • The seal is not concentric with the shaft, and is hitting the stuffing box I.D.

Discoloration. Caused by high heat. Stainless steel changes color at various temperatures. The following graph will give you some guidelines:

700-800 Straw Yellow 370-425
900-1000 Brown 480-540
1100 Blue 600
1200 Black 650

NOTE: To tell the difference between discoloration of the metal caused by high heat, and product attaching to the metal part, try to erase the color with a common pencil eraser. Discoloration caused by high heat will not erase off.

Some of the product is sticking to the metal surfaces restricting their movement.

  • Heat is the main cause. Heat will cause products to :
    • Solidify
    • Coke
    • Build a film.
    • Become very viscous
  • The product pressure has dropped. Many fluids solidify with a drop in pressure. Paint is a good example of this. The paint solidifies when the solvents evaporate.
  • Air or oxygen is getting into the system. It can enter from:
    • Valves above the water line.
    • Through the stuffing box.
    • The product was not deaerated.
    • The pump suction is not completely submerged.
    • The bypass return is too close to the pump suction.
    • The liquid is vortexing in the suction line.
    • A non O-ring elastomer is being used in the seal allowing air to enter the stuffing box when you are sealing a vacuum application.
  • The system protective oxide coating is depositing on the sliding metal components and restricting their movement. In almost all cases this passivated material is a ceramic. A good example of this ceramic coating is the Magnetite that forms on carbon steel.

A Teflon® coating is coming off some of the metal parts.

  • Be sure to remember that these coatings are very porous. They do not provide corrosion resistance. The product you are sealing will penetrate the Teflon® coating and then proceed to attack the base metal. If you want corrosion resistance you are going to have to sleeve the material with a layer of Teflon® at least 0.060 inches (1.5 mm) thick
  • A Teflon® coating is put on mechanical seal components for a couple of reasons
  • To stop solids or films from sticking to the seal component and interfering with the movement of the seal.
  • To provide a smoother surface for the dynamic elastomer (O-ring) to flex and roll.
  • To prevent an elastomer from attaching its self to the shaft during shut down periods. Without the Teflon® the elastomer can settle into the metal surface irregularities causing a high “break away torque”.


Broken parts.

  • Chemical attack is a common cause.
  • Excessive side load or high torque.
    • The seal faces are glued together because the product has solidified for some reason.
    • A cryogenic fluid is sticking the faces together.

Wear on one side of the drive lug or slot.

  • Vibration.
  • Slipstick.
  • The stationary is not perpendicular to the shaft.

The drive pins are falling out of the holder.

  • Corrosion.
  • Improper fit.
  • Bad part.
  • Excessive vibration.


Broken or cracked.

  • The stationary face is not perpendicular to the shaft causing excessive spring flexing in the metal “plastic range”. The spring material has “work hardened” and fatigued.
  • Chloride stress corrosion problems with 300 series stainless steel spring material.


  • Stressed material corrodes much faster than unstressed material. The springs are under severe stress.


  • If the product solidifies or crystallizes, it can clog springs exposed to the pumped fluid.
  • Be sure to distinguish between “cause and effect”. If the springs are located outside the liquid it means that the clogging probably happened after the seal failure.
  • Dirt or solids in the fluid can clog exposed springs. Most raw product has enough solids to do this.
  • The springs in some outside and cartridge mechanical seal designs are sometimes painted by maintenance personnel.


  • Almost always an assembly problem. The seal face drive lugs were not engaged in their anti-rotation slots. This is a problem with many seal designs. Check to see if your seals can come apart easily or if the drive lugs can change position when the seal is not compressed.

The drive lugs or slots are worn on both sides.

  • Excessive vibration.
  • The single spring, rubber bellows seal was not vulcanized to the shaft.
  • The stationary is not perpendicular to the shaft, causing excessive spring and lug movement in some designs.

Broken metal bellows.

  • Fatigue caused by over flexing of the bellows in the plastic range of the metal
  • Harmonic vibration.
  • Slipstick.
  • The discharge recirculation line is aimed at the thin bellows plates.
  • Excessive wear from solids in the stuffing box.
  • Faces sticking together as the product solidifies.
  • Chloride stress corrosion with 300 series stainless steel.


Because some of these metal bellows seals do not have a dynamic elastomer to provide vibration damping, some other means must be provided, or vibration will always be a problem.


Grooves or pits at the seal dynamic elastomer location.

  • Fretting.
  • Concentrated cell corrosion.
  • The rubber bellows did not vulcanize to the shaft/ sleeve.
  • The set-screws slipped on a hardened shaft or were not tightened properly. The seal faces stuck together causing the shaft to rotate inside the static elastomer.
  • Salt-water applications are particularly troublesome when a static elastomer or clamp is attached to the shaft. Pitting caused by the chlorides and the low pH of salt water are the main problems.

Rubbing at the wear ring location.

  • The pump is running off of its best efficiency point (BEP)
  • The shaft is bending.
  • Bad bearings.
  • Excessive temperature causing a thermal growth.
  • High temperature applications require a “center line pump design.
  • Sleeve is not concentric with the shaft, or the seal with the sleeve.
  • Bent shaft.
  • Unbalanced impeller or rotating assembly.
  • Pipe strain.
  • Misalignment between the pump and its driver


  • Stripped from over tightening.
  • Corroded. Check to see if you are using hardened set-screws. This type is normally supplied with most cartridge seals and can corrode easily.
  • Rounded Allen Head. Alan wrenches wear rapidly. They are an expendable tool.
  • The set screws have become loose.
    • Sleeve too hard. They are not biting in.
    • Sleeve too soft. They are vibrating loose.


Rubbing at the inside diameter of the gland

  • Partial rubbing on only one side.
    • The gland has slipped and is no longer centered over the shaft.
    • Improper installation. It was not centered over the shaft.
    • The shaft is bending.
    • Pipe strain.
    • The pump is operating off of its best efficiency point (BEP)
    • Misalignment between the pump and the driver.
  • Rubbing all around the inside diameter of the gland
    • The sleeve is not concentric with the shaft.
    • The seal is not concentric with the sleeve.
    • Bad bearings will cause the shaft to move in all sorts of directions.
    • A bent shaft.
    • Unbalanced impeller or rotating assembly.
    • Solids attached to the shaft, or trapped between the shaft and the gland.
    • Cavitation.
    • Water hammer


  • If there is evidence of rubbing the corrosion will be accelerated.


Gland passages clogged or not connected properly.

Please look at this API (American Petroleum Institute) gland. You can see some potential problems:

  • The Flush and quench connections (F&Q) can be mixed up and the lines reversed
  • The Flushing connection can be clogged or the pipefitting could be blocking the passage.
  • The Quench connection could be clogged also


Please refer to DB in the above illustration

Rubbing marks at the inside diameter of the seal gland

  • Partial rubbing at the inside diameter.
    • The API (American Petroleum Institute) gland has slipped.
    • Improper installation. The bushing was not centered to the shaft.
    • The shaft is bending because the pump is operating off its best efficiency point (BEP).
    • The gland bolt holes are often not concentric with the shaft/ sleeve.
    • Misalignment between the pump and its driver.
    • Excessive pipe strain.
  • Rubbing all around the inside diameter.
    • The shaft is not concentric with the sleeve.
    • The seal is not concentric with the sleeve.
    • Bad bearings.
    • Bent shaft.
    • Unbalanced impeller or rotating assembly
    • Cavitation.
    • Any severe vibration will cause this symptom
    • Thermal expansion of the shaft or sleeve

Erosion at the inside diameter of the stuffing box bushing

  • Dirt and solids are present in the discharge or suction recirculating fluid. The fluid accelerates through the close fitting bushing in the end of the stuffing box, increasing the rate of erosion. This can be a big problem if you are using suction re-circulation.

Rubbing on the ends of the restrictive or thermal bushing caused by the bushing rotating in the stuffing box. A snap ring, sleeve, etc did not positively retain the bushing.

  • A differential pressure across the bushing can push the bushing into the rotating portion of a mechanical seal.

  • This is similar to what happens with “back to back” dual seals when the stationary inside face is pushed into the inside rotating face.

Please notice that a “snap ring” has been installed inside the stuffing box to hold the stationary face if a pressure differential should occur.