REEP001

September 1995

Process Industry PracticesMachinery

REEP001Seal Flush and Lubrication Guidelines for

Centrifugal Pumps

PURPOSE AND USE OF PROCESS INDUSTRY PRACTICES

In an effort to minimize the cost of process industry facilities, this Practice hasbeen prepared from the technical requirements in the existing standards of majorindustrial users, contractors, or standards organizations. By harmonizing these technicalrequirements into a single set of Practices, administrative, application, and engineeringcosts to both the purchaser and the manufacturer should be reduced. While this Practiceis expected to incorporate the majority of requirements of most users, individualapplications may involve requirements that will be appended to and take precedence overthis Practice. Determinations concerning fitness for purpose and particular matters orapplication of the Practice to particular project or engineering situations should not bemade solely on information contained in these materials. The use of trade names fromtime to time should not be viewed as an expression of preference but rather recognizedas normal usage in the trade. Other brands having the same specifications are equallycorrect and may be substituted for those named. All practices or guidelines are intendedto be consistent with applicable laws and regulations including OSHA requirements. Tothe extent these practices or guidelines should conflict with OSHA or other applicablelaws or regulations, such laws or regulations must be followed. Consult an appropriateprofessional before applying or acting on any material contained in or suggested by thePractice.

©Process Industry Practices (PIP), Construction Industry Institute, TheUniversity of Texas at Austin, 3208 Red River Street, Suite 300, Austin,Texas 78705. PIP member companies may copy this practice for their internaluse.

3pr96 Minor format changes.

2pr96 Minor format changes.

Not printed with state funds.

September 1995

Process Industry Practices Page 1 of 15

Process Industry PracticesMachinery

REEP001Seal Flush and Lubrication Guidelines for

Centrifugal Pumps

Table of Contents

1. Introduction ..................................21.1 Purpose .............................................21.2 Scope ................................................2

2. References....................................22.1 Industry Codes and Standards ...........2

3. Seal Flush Plans...........................23.1 General..............................................23.2 API Plan 1 .........................................33.3 API Plan 2 .........................................33.4 API Plan 11........................................33.5 API Plan 12........................................43.6 API Plan 13........................................43.7 API Plan 21........................................53.8 API Plan 22........................................53.9 API Plan 23........................................53.10 API Plan 31.......................................53.11 API Plan 32.......................................63.12 API Plan 41.......................................63.13 API Plan 51.......................................73.14 API Plan 52.......................................7

3.14.1 General ..................................73.14.2 Seal Pot .................................73.14.3 Auxiliary Piping/Tubing...........8

3.14.4 Seal Pot Pressure Switch....... 83.14.5 Seal Pot Level Switches......... 93.14.6 Buffer Fluid ............................ 9

3.15API Plan 53 ....................................... 93.15.1 General.................................. 93.15.2 Seal Pot Low Level Switch... 103.15.3 Seal Pot Low Pressure

Switch.................................. 103.16 API Plan 54 .................................... 103.17 API Plan 61 .................................... 103.18 API Plan 62 .................................... 11

4. Lubrication Methods forBearings......................................114.1 General ........................................... 114.2 Product Lubricated Bearings............ 114.3 Lubrication of Antifriction Bearings .. 11

4.3.1 General .................................. 114.3.2 Grease Method....................... 114.3.3 Wet Sump Method.................. 124.3.4 Dry Sump Method................... 14

4.4 Pressure Fed Lubrication................. 144.5 Lubricant Contamination

Considerations................................. 15

PIP REEP001Seal Flush and Lubrication Guidelines for Centrifugal Pumps September 1995

Page 2 of 15 Process Industry Practices

1. Introduction

1.1 Purpose

The purpose of this Practice is to provide designers with seal flush and lubricationguidelines for centrifugal pumps for chemical plant and refinery applications.

1.2 Scope

This Practice covers guidelines for application of seal flush plans and lubricationconsiderations for centrifugal pumps.

2. References

The following references contain additional information that may be useful to the designer:

2.1 Industry Codes and Standards

• American Petroleum Institute (API)

– Std. 610 - Centrifugal Pumps for Refinery Service

– Std. 682 - Shaft Sealing Systems for Centrifugal and Rotary Pumps

• American Society for Mechanical Engineers (ASME)

– Boiler and Pressure Vessel CodeSection II - MaterialsSection VIII, Division 1 - Pressure Vessels

In this Practice the ASME Boiler and Pressure Vessel Code is referred to as theASME Code for convenience.

– B73.1 M - Specification for Horizontal End Suction Centrifugal Pumps forChemical Process

– B73.2 M - Specification for Vertical In-Line Centrifugal Pumps for ChemicalProcess

3. Seal Flush Plans

3.1 General

Shaft sealing systems are discussed in API Std. 682 in general terms. Additionalinformation on shaft sealing systems is available in Appendix D of API Std. 610.

Seal life can be extended by designing systems that provide cool and clean fluids to theseal cavity and by using bearings and a shaft stiffness that minimize motion of theseals.

PIP REEP001September 1995 Seal Flush and Lubrication Guidelines for Centrifugal Pumps


Seal flush guidelines in Sections 3.2 through 3.18 of this Practice are provided toassist in the selection of standardized seal flush plans as defined in Appendix D of APIStd. 610 and in Figure A2 of ASME B73.1M and ASME B73.2M.

Selection of an appropriate seal flush plan must take into consideration normal andtransient operating conditions, including standby condition in which pumps withrecirculating flush system have no flow through the seal chamber. Seal materials mustbe suitable for expected temperatures and pressures during standby and warm-up (orcool-down). A continuous flush from an external source may be required if sealcomponents cannot tolerate anticipated conditions in the seal chamber when the pumpis idle.

3.2 API Plan 1

API Plan 1 (ASME Plan 7301) takes fluid from the pump discharge, reduces thepressure as it passes through an orifice, and injects the fluid into the seal cavity (sealface) area through an internal passageway. The fluid then flows from the seal cavity tothe back side of the impeller and then back into the process stream.

The purpose of API Plan 1 is to keep fluid from stagnating in the seal cavity.Stagnation may result in excessive seal cavity temperature rise and buildup ofcontaminants from normal wear.

API Plan 1 should not be used with dirty fluids.

3.3 API Plan 2

API Plan 2 (ASME Plan 7302) has a dead-end seal chamber with no circulation offlushing fluid, but it has plugged connections in the seal chamber for possible futurecirculating fluid. A water-cooled stuffing box jacket may be specified to providecooling.

API Plan 2 can be used with clean fluids with high specific heats, such as water, inrelatively low speed pumps.

Extreme caution should be used if API Plan 2 is used in light hydrocarbon serviceswith low specific heats because of excessive seal cavity temperature rise that cancause vaporization of the fluid.


3.4 API Plan 11

API Plan 11 (ASME Plan 7311) takes fluid from the pump discharge, reduces itspressure as it passes through an orifice, and injects it into the seal cavity (seal face)area through external piping or tubing. Fluid then flows from the seal cavity to theback side of the impeller and then back into the process stream.

The purpose of API Plan 11 is to provide cooling by keeping fluid from stagnating inthe seal cavity. Stagnation may result in excessive seal cavity temperature rise andbuildup of contaminants from normal wear.




3.5 API Plan 12

API Plan 12 (ASME Plan 7312) is identical to API Plan 11 except for an additionalY-strainer upstream of the orifice and the seal cavity.

Comments on API Plan 12 are the same as those on API Plan 11 with the additionalcomment that the coarse filtration provided by a Y-strainer may be of little or no valuefor protecting the seal, other than keeping the orifice from plugging.

Note: API Plan 12 has been deleted in API Standard 610, 8th edition.

3.6 API Plan 13

API Plan 13 (ASME Plan 7313) provides circulation from the seal cavity through anorifice back to the pump suction. The most commonly used function of API Plan 13 isto reduce pressure in the seal cavity on pumps that generate high seal cavity pressures,such as a vertical turbine pumps that have discharge pressure on the throat bushingdirectly under the seal cavity.

In order to get flow through the seal cavity, it is imperative to bleed off the seal cavitypressure through an orifice back to the pump suction.

On vertical turbine pumps, API Plans 1, 11, 12, 21, 22, 31, or 41 must be used inconjunction with API Plan 13. Caution must be taken when using API Plan 13 not toreduce the seal cavity pressure below the process fluid vapor pressure.

API Plan 13 is also useful in high-head pumps in which the use of an API Plan 11requires a small orifice [less than 3 mm (1/8-inch)] that can be easily plugged orproduces an excessive flush flow rate.

In pumps that have discharge heads greater than 300 meters (1,000 feet), the use ofmultiple orifice breakdown that increases orifice sizes, may be desirable. The use ofmultiple orifice breakdown also reduces noise and provides less orifice wear than thesmaller single orifice.

API Plan 13 should not be used on pumps in which specific impeller designs causeseal chamber pressure to approach or fall below the suction pressure of the pump.Typical of this design is the reverse vane impeller. Under these conditions there may beinadequate differential pressure to cause flow sufficient to cool the seal assembly,resulting in mechanical damage to the seal faces.

When pumping light hydrocarbons or steam condensate at low flow rates, much of thedriver power heats the process fluid due to pump inefficiency. Heating of the processfluid can cause vapor formation and possible vapor locking of the pump.

A modified version of API Plan 13 (referred to as API Plan 14 in the 8th edition ofAPI Std 610) that takes seal cavity fluid through an orifice back to the vapor portionof the suction vessel provides even better protection for the seal. The seal cavitybypass provides a greater flow rate, and this improves the potential for vapor removal.API Plan 14 is also often used successfully for highly volatile fluids in systems withmarginal net positive suction head available (NPSHA) which will otherwise notoperate due to cavitation. If it is not possible to install a line back to the suction vessel,injecting into suction piping at least 5 meters (15 feet) upstream of the inlet flange at a



point above the seal cavity elevation may be an acceptable alternative. This alternativemay allow time for the vapor to condense.

3.7 API Plan 21

API Plan 21 (ASME Plan 7321) takes fluid from the pump discharge through anorifice and heat exchanger and then injects the fluid into the seal cavity. This isbasically an API Plan 11 with the addition of the heat exchanger.

The purpose of API Plan 21 is to provide a cooled flush to the seal. The need for acooled seal flush can vary greatly depending on the process fluid, type of seal used,and materials of construction for the seal. Pump and seal manufacturers should beconsulted for specific recommendations.

When pumping hot water at sea level, a cooled seal flush is recommended for pumpingtemperatures above 66ºC (150ºF). This temperature should be adjusted for higherelevations to maintain the temperature in the seal chamber approximately 39°C (70°F)below the atmospheric boiling temperature of water.

The heat exchanger may use water as a cooling medium or an air fin convective/airfin-fan if water is scarce. Alternatively, the exchanger may use a suitable process fluidas the cooling medium.

3.8 API Plan 22

API Plan 22 (ASME Plan 7322) is identical to API Plan 21 except for an additionalY-strainer upstream of the orifice.

Comments to API Plan 22 are the same as those on API Plan 21, with the additionalcomment that the coarse filtration provided by a Y-strainer may be of little or no valuefor protecting the seal other than keeping the orifice from plugging.


3.9 API Plan 23

API Plan 23 (ASME Plan 7323) incorporates a pumping ring on the seal that providesrecirculation of the process fluid from the seal cavity through a heat exchanger andback to the seal.

API Plan 23 has an advantage over API Plan 21 because slightly less power isconsumed, but more importantly, the cooled seal flush fluid does not go back into theprocess stream. Another advantage over API Plan 21 is that less cooling water isrequired because the cooler removes only seal face generated heat, plus heat conductedfrom the pump casing by the shaft and seal chamber.

3.10 API Plan 31

API Plan 31 (ASME Plan 7331) takes dirty process fluid from the pump dischargeinto an inertial separator. Clean fluid comes off the top of the inertial separator,through the orifice, to the seal cavity, to the back side of the impeller, and then backinto the process stream. Dirty fluid comes off the bottom of the inertial separator intothe pump suction.



If the process stream is very dirty or is a slurry, API Plan 31 typically is inadequateand is not recommended. (See Section 3.11 of this Practice.) Also, some solids with adensity less than twice that of the process fluid do not centrifuge out of suspensioneffectively, thus making the inertial separator ineffective.

Some pump manufacturers offer an optional internal inertial separator with internalpassageways that eliminates costly external piping/tubing, and can be used in lieu ofAPI Plan 11 (ASME 7311). An external separator may be the best choice ifcontaminants are excessive or extremely abrasive, resulting in the need for periodiccleaning or replacement of the separator. Below is typical internal inertial separatorparticle removal performance:

PARTICLE SIZE PERCENT REMOVED

2.5 micron 875.0 micron 948.5 micron 96-99

3.11 API Plan 32

API Plan 32 (ASME Plan 7332) is used to inject an external source of clean and/orcooled fluid into the seal cavity. This seal flush fluid goes from the seal cavity to theback side of the impeller and then into the process stream.

Requirements/conditions under which API Plan 32 should be used are as follows:

• Requirement for a clean flush to the seal if the process fluid is extremely dirty or isa slurry that prohibits the use of API Plan 31.

• Requirement for a cooled flush to the seal if the process fluid is too hot or if coolingwater is not available for an API Plan 21.

• Requirement for a non-corrosive seal flush to provide a buffer zone in the sealcavity to prevent corrosive process fluid from damaging the seal. An example is anisobutane flush into a hydrofluoric acid pump.

• Requirement for reduction of flashing or air intrusion (in vacuum service) acrossseal faces by providing a flush that has a lower vapor pressure or that raises theseal chamber pressure to an acceptable level.

Caution: The seal flush pressure must be greater than the seal cavity pressure. Thepump manufacturer should be consulted for recommendations. Also, the fluid flushmust be compatible with the process fluid because it will leak into the process fluid.

3.12 API Plan 41

API Plan 41 (ASME Plan 7341) is the same as API Plan 31 except that a heatexchanger is used to cool the flush going to the seal cavity. If cooling water is notavailable, an air cooled heat exchanger may be used. Occasionally, a cool processstream is used as the cooling fluid.

Caution: Proper selection of heat exchanger materials, pressure ratings, andtemperature ratings is required.



3.13 API Plan 51

API Plan 51 (ASME 7351) is most effectively applied to vertical pumps. API Plan 51provides for a non-pressurized, dead-end blanket of buffer fluid on the outboard sideof the mechanical seal.

Some type of auxiliary sealing device is necessary to keep the buffer fluid from leakingto the atmosphere or on the ground. API Plan 51 is typically used with single seals.

API Plan 51 is used to:

• Prevent formation of ice on the outboard side of the mechanical seal that can causeproblems with the seal faces. This is required for cryogenic and many lighthydrocarbon services at start-up below 0ºC (32ºF). Methanol is frequently used asa buffer fluid. Special attention is needed when using methanol or ethanol becausethey evaporate through any vent to the atmosphere or to a low pressure area.

• Prevent formation of crystals on atmospheric or outboard side of the mechanicalseal. With certain fluids, such as caustic, crystals form on the atmospheric side of aseal when normal seal leakage comes into contact with air. By providing a blanketof buffer fluid such as glycol, air is prevented from reaching the outside of the seal,thus preventing crystal formation.


3.14 API Plan 52

3.14.1 General

API Plan 52 (ASME Plan 7352) is typically used with a tandem sealarrangement and allows a buffer fluid to provide lubrication and cooling tothe secondary (outboard) seal.

3.14.2 Seal Pot

A non-pressurized seal pot with a capacity of 8 to 20 liters (2 to 5 gallons) isconnected to the seal housing with supply and return piping or tubing. Thepiping/tubing should be arranged to allow the buffer fluid to thermosiphonand the tandem seal design should provide pumping action (centrifugal oraxial flow pumping ring) to cause forced circulation of the buffer fluid inorder to remove heat generated by the seals.

Certain applications may require a heat exchanger either in the supply line oras cooling coils in the seal pot to cool the buffer fluid and enhancethermosiphoning.

The seal pot should be high enough to provide a minimum level of bufferfluid of 30 cm (1 foot) above the seal. However, the recommended level is 1meter (3 feet). Additionally, the supply and return piping/tubing from theseal pot to the seal should be adequately sized and arranged to minimizehead losses. Piping/tubing must also be arranged to avoid a vapor trap in thereturn line from the seal to the seal pot.



Pressurized seal pots (greater than 15 psig) with an inside diameter greaterthan 15 cm (6 inches) shall be designed and constructed in accordance withASME Code Section VIII using the material properties from ASME CodeSection II, Part D.

All seal pots require ASME Code Stamping unless exempted by a localjurisdiction or governing agency.

The buffer fluid level in the seal pot must be maintained above the returnline entry position in the seal pot to achieve and maintain the thermosiphoneffect. If the fluid falls below this level, and if circulation is dependent onlyon the thermosiphon effect, flow will stop, and cause seal damage. A meansof monitoring this low critical level must be provided in the seal pot and maybe a local sight glass or a remote low level alarm system.

If the primary (inboard) seal leaks, the process fluid leaks into the bufferfluid. A pressure switch or a high level switch in the seal pot can be used todetect this leakage.

3.14.3 Auxiliary Piping/Tubing

A flow indicator is sometimes specified in the return line to the seal pot toensure that circulation is occurring. In general, flow indicators are notrecommended because they cause extra pressure drop, thus impeding flow.

The return line to the seal pot should be noticeably warmer to the touchwhen compared to the supply line to the mechanical seal.

3.14.4 Seal Pot Pressure Switch

For process fluids with vapor pressure greater than atmospheric pressure, apressure switch is typically used to detect pressure buildup in the seal pot.

The seal pot is usually vented to a flare through an orifice that is typically 3mm (1/8-inch) in diameter. Normal seal leakage vaporizes and vents throughthis orifice, but if excessive leakage cannot vent fast enough, the pressurebuildup in the seal pot will be detected by the pressure switch.

For most light hydrocarbon applications, the pressure switch should be set100 - 200 kPa (15 - 30 psig) above the flare system pressure. The pressureswitch could be set higher, but more leakage would occur before detection.

Field adjustable pressure switches are recommended. A block valve betweenthe seal pot and the orifice allows the operator to stop leakage to the flareand to keep the pump running on the secondary seal until the pump can bescheduled for maintenance. Seal pots and seal flush tubing/piping that can beblocked from atmospheric venting should be designed for maximum pumpdischarge pressure.

A pressure gauge should be provided on the seal pot to determine the internalpressure. Seal pot pressure must be vented before depressurizing the pump,or back pressure on the primary seal can cause the primary seal faces toopen up and dump buffer fluid into the pump.



3.14.5 Seal Pot Level Switches

For process fluids with vapor pressures lower than atmospheric pressure orfor process fluids with entrained gases, (for example, carbon dioxide, amine)that vaporize with leakage across the seal, a high level switch in the seal potis typically used to detect seal leakage.

If the buffer fluid level reaches the high level switch, the operator can lowerthe level, and then determine how long it takes for the level to build back up.Build up frequency is the basis for deciding when to conduct maintenance.Because of the low vapor pressures, a pressure gauge on the seal pot maynot be necessary.

Some purchasers specify a low level switch on the seal to detect a loss ofbuffer fluid. Loss of buffer fluid typically occurs across the secondary(outboard) seal. Buffer fluid can also be lost past an o-ring in the glandplate, through a leaking piping/tubing fitting, through a leaky drain valve,etc. Loss of the buffer fluid causes failure of the secondary (outboard) seal.

3.14.6 Buffer Fluid

It is the purchaser's responsibility, not the pump vendor's, to select a bufferfluid that is compatible with the process fluid and that has lubricatingproperties for the secondary (outboard) seal. The buffer fluid should be non-corrosive to the seal pot and piping, should not be too viscous, and shouldnot freeze in cold weather.

3.15 API Plan 53

3.15.1 General

API Plan 53 (ASME Plan 7353) is typically used with double seals and issimilar to an API Plan 52 except that it is a pressurized system with aminimum blanket pressure 140 kPa (20 psi) higher than the zone between theprimary (inboard) seal and the back side of the impeller.

Occasionally, if process pressures vary significantly, the blanket pressure isset at the relief valve setting. If process pressure exceeds 3,500 kPa (500psig), setting the blanket pressure at the relief valve setting results inunnecessary secondary seal stress and reduced reliability. A more effectiveway to minimize stress on the secondary (outboard) seal is by the applicationof a controlled differential blanket pressure at a level 140 kPa (20 psig)higher than the zone between the primary (inboard) seal and the back side ofthe impeller.

API Plan 53 provides lubrication and cooling for both the primary (inboard)and secondary (outboard) seals. Supply and return piping/tubing should bearranged to allow the buffer fluid to thermosiphon. The double seal designshould provide pumping action to cause forced circulation of the buffer fluidin order to remove heat generated by the seals. Certain applications mayrequire an exchanger in the supply line or cooling coils in the seal pot to coolthe buffer fluid and enhance thermosiphoning. A sight flow indicator in the



return line to the seal pot is not recommended. Occasionally, a separatepump is used to provide positive circulation.

3.15.2 Seal Pot Low Level Switch

A low level switch in the seal pot detects a loss of buffer fluid from leakageacross the primary and/or secondary seals, or leakage through some otherpath, such as loose fittings. A means of adding make-up buffer fluid underpressure to the seal pot while the pump is running is necessary, or the pumpmust be shutdown and depressurized, and the seal pot depressurized. Themake-up buffer fluid is then added, the seal pot repressurized, and finally thepump is repressurized and restarted.

3.15.3 Seal Pot Low Pressure Switch

A low pressure switch in the seal pot is used to detect loss of pressurizationof the buffer system. Loss of buffer fluid pressure can upset the primary(inboard) seal, thus allowing process fluid to flow into the API Plan 53system. Typically, a constant external pressure source prevents loss ofproper pressurization.

3.16 API Plan 54

API Plan 54 (ASME Plan 7354) is typically used with double seals and allows forcirculation of a clean high pressure fluid from an external system to supply lubricationand cooling for both the primary (inboard) and secondary (outboard) seals.

API Plan 54 does not have instruments for detection of seal leakage. Leakage of thesecondary (outboard) seal can be detected visually by leakage to the atmosphere. APIPlan 54 is also used occasionally with tandem seals with a low pressure clean fluidbeing used to provide lubrication and cooling of the secondary (outboard) seal.Leakage across the primary (inboard) seal is more difficult to detect than when usingan API Plan 52.

Careful consideration should be given to the reliability of the barrier fluid source. Ifthe barrier fluid source is interrupted or contaminated, expensive seal failures mayoccur.

Occasionally, if process pressures vary significantly, the seal flush pressure is set atthe relief valve setting. If process pressure exceed 3,500 kPa (500 psig), setting theseal flush pressure at relief valve setting results in unnecessary secondary seal stressand reduced reliability. A more effective way to minimize stress of the secondary(outboard) seal is by application of a differential back pressure controlled at a level140 kPa (20 psig) greater than the zone between the primary (inboard) seal and theback side of the impeller.

3.17 API Plan 61

API Plan 61 (ASME Plan 7361) provides plugged connections in the gland plate toallow for future use as an API Plan 62.



3.18 API Plan 62

API Plan 62 (ASME Plan 7362) allows an external fluid quench (steam, gas, water,etc.) between the outboard seal and the throttle bushing or auxiliary sealing device.Applications include steam quench on hot oil pumps to prevent coking, water quenchon caustic or salt pumps to prevent contact with air (thus preventing the formation ofcrystals on the outboard side of the seal), and nitrogen quench (purging) to carrycertain vapors away that may leak across seal faces.

4. Lubrication Methods for Bearings

4.1 General

Lubrication method used for centrifugal pump bearings depends on the type ofbearing, the size of the pump, and cost considerations.

4.2 Product Lubricated Bearings

Product lubricated bearings are typically used in vertical and sealless pumps that havesleeve bearings. The product is used as a hydrodynamic fluid for centering the pumpshaft within one or more sleeve bearings.

Except for sealless pumps, sleeve bearings are typically made of rubber, carbon,carbon filled PTFE, or metal, often bronze. Compatibility of the pumped fluid with thebearing material is critical to the success of product lubricated bearings. If the pumpedfluid is chemically active or contains solids, special consideration is required formaterials.

In some cases, an external source of clean product may be required for the lubricationof the bearings.

Product lubricated bearings may have axial or helical grooves.

4.3 Lubrication of Antifriction Bearings

4.3.1 General

Lubrication methods for antifriction bearings include grease, wet sump, anddry sump.

The reliability of antifriction bearings is heavily influenced by the bearingfit, alignment, and the temperature and cleanliness of the lubricant.Consequently, the lubricant should be maintained uncontaminated and at atemperature low enough to preclude its deterioration.

4.3.2 Grease Method

The grease lubrication method is typically limited to non-critical pumps thatoperate at relatively low speeds and temperatures, and that have a driverpower of 7.5 kW (10 hp), or less, for horizontal pumps, and 45 kW (60 hp),or less, for vertical pumps.



The grease lubrication method is used more often in vertical pumps than inhorizontal pumps.

Grease may be packed in the bearing and sealed at the factory or it may bein the bearing housing surrounding the bearing. If the grease is in the bearinghousing, whether on the pump or driver, the bearing vent plug should beremoved and the vent left open until the pump has operated at a stabletemperature. This procedure minimizes the common tendency to over greasethe bearing.

4.3.3 Wet Sump Method

4.3.3.1 General

The wet sump lubrication method is the most common incentrifugal pumps. This method is also referred to as oil flooded.

Variations of the wet sump method are the simple-wet-sumpmethod, the wet-sump-with-ring-oil method, the wet-sump-with-flinger method, and the wet-sump-with-purge-mist method.

4.3.3.2 Simple-Wet-Sump Method

In the simple-wet-sump lubrication method, the lower section ofthe bearing housing serves as a small sump. The sump oil levelshould be maintained at the centerline of the lowest rollerelement in the bearing. This is accomplished by a constant leveloiler with a typical capacity of 100 cc (4 ounces). Problemsencountered with the simple-wet-sump method are the following:

• If the oil level is high, frothing and foaming may occur.Unnecessary heat will be generated and additional power isrequired.

• Proper level is confined to a small range. If the oil level fallsbelow the lower rolling element, no further lubrication ispossible.

• With vented bearing housings, there is a tendency for watervapor to condense inside the bearing housing, particularly onstandby units. Water condensate displaces the lubricant andcauses pitting of the lower rotating elements, resulting inshortened bearing life.

The simple-wet-sump method is the standard lubrication methodon many ASME B73.1 pumps. If contamination or heat buildupis possible, other lubrication methods should be considered toimprove reliability.

4.3.3.3 Wet-Sump-With-Ring-Oil Method

In the wet-sump-with-ring-oil method, a ring rides on the top ofthe shaft and within the oil sump. The ring is not attached and



merely rests on top of the shaft. The ring typically rotates atabout 50% of the shaft speed.

The oil level must be maintained so that the bottom of the ring isimmersed in the oil sump, thus lifting and distributing the oil asthe ring turns.

One advantage of the wet-sump-with-ring-oil method, ascompared to the simple-wet-sump method, is that the oil level isbelow the lowest rolling element, thus eliminating frothing andreducing heat and energy requirements.

Maintenance of the proper oil level is critical to reliableoperation. The ring bore should be immersed in the oil 6 mm to 9mm (1/4-inch to 3/8-inch).

Problems can be encountered on startup or in cold climates if theoil in the sump is too viscous. If the oil is too viscous, the ringmay rotate at a considerably reduced speed and may be unable toprovide oil to the rolling elements.

4.3.3.4 Wet-Sump-With-Flinger Method

In the wet-sump-with-flinger method, a flinger (disc) is attachedto the pump shaft. A flinger works better than a ring when the oilis very viscous. The flinger must be immersed in the oil in thesame manner as in the ring oil method.

The wet-sump-with-flinger method is the standard lubricationmethod for most API single stage overhung pumps. This methodis generally more reliable than the simple-wet-sump method.

4.3.3.5 Wet-Sump-With-Purge-Mist Method

The wet-sump-with-purge-mist method incorporates a variety offeatures from the other wet sump methods, plus an oil mist purgethat is typically supplied from a central oil mist generatingconsole.

The main advantage of the wet-sump-with-purge-mist method isthe elimination of atmospheric contamination. This increases themean time between failure of bearings.

The wet-sump-with-purge-mist method does not take fulladvantage of the energy savings that can be attributed to the drysump method.

Drain cups should be installed with the wet-sump-with-purge-mist method because the sump oil level increases gradually.



4.3.4 Dry Sump Method

The dry sump lubrication method (pure oil mist) uses a central oil mistgenerator that provides compressed dry air, saturated with oil mist, directlyto the bearing housing.

The main advantages of the dry sump method are as follows:

• The central oil mist generator that serves several pumps requires lessmanpower for routine maintenance servicing.

• Since the lubricating oil is once through, bearing wear particles arewashed out and not recycled. The need for oil changes is eliminated.

• Antifriction bearings tend to operate at a cooler temperature compared tosump oil systems.

• By adding a transparent collection chamber at the bottom of the drysump, oil mist condensate can be collected and examined for colorchanges or spectrometric examination. Thus, early detection of bearingdistress is possible.

• 50% less lubricating oil will be consumed compared to the wet sumpmethod, even with the once through oil.

• Less energy is consumed compared to the wet sump method.

• The positive pressure within the bearing housing precludes ingress ofatmospheric contaminants, thus reducing the potential for corrosion orwear from atmospheric contaminants.

• Reduction of bearing failures and maintenance costs.

4.4 Pressure Fed Lubrication

Pressure fed lubrication may be used for pumps with hydrodynamic radial or thrustbearings. The pressure fed lubricant acts both as a coolant and a lubricant. This typeof lubrication system is almost never used for pumps with driver power less than225 kW (300 hp).

Hydrodynamic bearings are more commonly used on horizontal between-bearing typepumps. They are seldom used on overhung type pumps. Hydrodynamic bearings aretypically lined with bearing babbitt. Babbitt materials lose strength rapidly withincreasing temperature.

The oil film in pressure fed lubrication may be as thin as 0.005 mm (0.0002-inch).Therefore, the oil should be filtered to remove particles larger than the minimum oilfilm thickness.

Because the oil also serves as a coolant, pressure fed lubrication should have oilcoolers. The coolers are typically water cooled or fin fan.

API Std.610 should be used as a guide for long life pumps in main process streamservices that use pressure fed lubrication. Large utility pumps, intermittent dutypumps, or pumps with integral speed increasing gear boxes may use a manufacturer’s



standard force fed lubrication system if it has filtration, cooling, prelube pump, andindications of pressure and temperature.

4.5 Lubricant Contamination Considerations

Pumps that are outdoors, especially standby pumps, can have problems withcontamination of the bearing lubricant.

For new facilities with many pumps, it may be economically feasible to use the wet-sump-with-purge-mist lubrication method (4.3.3.5) or the dry sump lubrication method(4.3.4) to assist in keeping the bearing lubricant uncontaminated. These lubricationmethods can be used with standard lip seals for bearing isolation.

For facilities with only a few pumps, it is probably more economical to use the simple-wet-sump lubrication method (4.3.3.2) , the wet-sump-with-ring-oil lubrication method(4.3.3.3), or the wet-sump-with-flinger lubrication method (4.3.3.4). If theselubrication methods are used, they should be used in conjunction with the followingfeatures for bearing isolation:

• Labyrinth-type bearing isolation seals that provide a positive static seal ormagnetic-type bearing isolation seals. These types of bearing isolation sealsprovide a tight seal that precludes the ingress of atmospheric contaminants. Somelabyrinth-type bearing isolation seals do not provide an atmospherically tight sealin static conditions.

• A diaphragm expansion chamber, occasionally referred to as a vent, that istypically cylinder shaped and has an internal elastomeric diaphragm that precludesthe ingress of atmospheric contaminants.

• A bullseye-type level gauge to observe bearing oil level and eliminate the constantlevel oiler. The constant level oiler does not function properly with diaphragmexpansion chamber and bearing isolation seals that provide tight sealing of thebearing housing. Internal pressures vary from slightly positive to slightly negativeas the operating temperatures vary throughout the day.

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