Normas Texaco GEMS P-G-2 - Guide for Selection of Pumps

MAR 96 GUIDE FOR SELECTION OF PUMPS GEMS P-G-2

PAGE 1 OF 32©TEXACO GENERAL ENGINEERING DEPARTMENT

TABLE OF CONTENTSPAGE

1. SCOPE .............................................................. 2

2. REFERENCES......................................................... 2

2.1 Purchaser Specifications ..................................... 22.2 Purchaser Drawings ........................................... 22.3 Industry Codes and Standards ................................. 2

3. DEFINITIONS ........................................................ 3

4. CLASSIFICATION OF PUMPS ............................................ 4

4.1 Centrifugal Pumps ............................................ 44.2 Positive Displacement Pumps .................................. 8

5. SELECTION OF PUMPS ................................................. 10

6. SELECTION OF PUMP DRIVERS .......................................... 10

7. GEARS .............................................................. 10

8. MECHANICAL SEALS ................................................... 10

9. COUPLINGS .......................................................... 11

TABLES

1 Selection Criteria for Centrifugal, Reciprocating, and Rotary Pumps2 Comparison of Metering Pumps3 Driver Selection Criteria4 Gear Selection Criteria

FIGURES

1 Centrifugal or Positive Displacement Pump Selection2 Centrifugal Pump Selection3 API Centrifugal Pump Selection4 ASME Pump Selection5 Positive Displacement Pump Selection6 Horizontal (Overhung) Centrifugal Pumps7 Vertical In-Line Centrifugal Pumps8 Between Bearings Centrifugal Pumps9 Vertically Suspended Centrifugal Pumps10 Vertical Turbine Centrifugal Pump11 Canned Motor Centrifugal Pump12 Magnetic Drive Pump13 Submersible and Horizontal Self Priming Centrifugal Pumps14 Piston and Packed Plunger Positive Displacement Pump15 Diaphragm Positive Displacement Pump16 Rotary Positive Displacement Pumps (Gear, Lobe, and Vane)17 Rotary Positive Displacement Pumps (Screw, Progressive Cavity, and

Peristaltic)



1. SCOPE

This guide shall be used to determine the pump normally recommended fortypical applications.

2. REFERENCES

2.1 Purchaser Specifications

This specification contains references to the following Purchaserspecifications:

1. GEMS L-2M, “Induction Motors 200 HP and Smaller”.

2. GEMS L-3M, “Form Wound Motors 250 HP to 1500 HP”.

3. GEMS L-5M, “Large Special Purpose Induction Motors”.

4. GEMS P-2M, “Heavy Duty Centrifugal Pumps (API 610)”.

5. GEMS P-6M, “General Purpose Steam Turbines”.

6. GEMS P-7M, “Special Purpose Steam Turbines”.

7. GEMS P-17M, “Special Purpose Gear Units for Refinery Services”.

2.2 Purchaser Drawings

This specification contains references to the following Purchaserdrawings:

None.

2.3 Industry Codes and Standards

This specification contains references to the following industry codesand standards:

2. 3 .1 American Petroleum Institute (API)

1. 610, “Centrifugal Pumps for Petroleum, Heavy DutyChemical, and Gas Industry Services”.

2. 674, “Positive Displacement Pumps - Reciprocating”.

3. 675, “Positive Displacement Pumps - Controlled Volume”.

4. 677. “General Purpose Gear Units for Refinery Service”.

5. 682, “Shaft Sealing Systems for Centrifugal and RotaryPumps”.

2. 3 .2 American Society of Mechanical Engineers (ASME)

1. B73.1M, “Horizontal End Suction Centrifugal Pumps forChemical Process”.

2. B73.2M, “Vertical In-Line Centrifugal Pumps for ChemicalProcess”.

2. 3 .3 Process Industry Practices (PIP)

1. REPAP001, “Recommended Practice for Application ofCentrifugal Pumps”.

2. RESP73H, “Specification for Horizontal End SuctionCentrifugal Pumps”.



3. RESP73V, “Specification for Vertical Centrifugal Pumps”.

3. DEFINITIONS

1. Casing, Axially Split - Pump case split parallel to pump shaft.

2. Casing, Radially Split - Pump case split transverse to pump shaftaxis.

3. Diffuser - Pump design in which the impeller is surrounded bydiffuser vanes where the gradually enlarging passages change liquidvelocity head into pressure head.

4. Double Acting - Liquid is discharged during both forward and returnstrokes of the piston.

5. Duplex - Pump with two plungers or pistons.

6. Head, Acceleration - Pressure change due to changes in velocity inthe piping system.

7. General Purpose Equipment - Equipment that is spared or which isnot critical to the operation of a critical unit.

8. Impeller - Bladed member of rotating assembly of a centrifugal pumpwhich imparts force to liquid.

9. Net Positive Suction Head (NPSH) - Total suction head in meters(feet) of liquid absolute determined at suction nozzle and referredto datum elevation, minus the vapor pressure of liquid in meters(feet) absolute. The datum elevation is the shaft centerline forhorizontal pumps, the suction nozzle centerline for vertical in-line pumps, and the top of the foundation for other vertical pumps.

10. Net Positive Suction Head Available (NPSHA) - NPSH in meters (feet)of liquid determined by the Purchaser for the pumping system withthe liquid at rated flow and normal pumping temperature.

11. Net Positive Suction Head Required (NPSHR) - NPSH in meters (feet)determined by Supplier testing, usually with water. NPSHR ismeasured at the suction flange and corrected to the datumelevation. NPSHR is the minimum NPSH at rated capacity required toprevent a head drop of more than 3% (first stage head in multistagepumps) due to cavitation within pump.

12. Recirculation - Controlling the quantity of flow through a pump bybypassing discharge liquid back to suction.

13. Shut-off - Point on pump curve at which flow is zero, usually pointof highest total dynamic head.

14. Simplex - Pump with one plunger or piston.

15. Special Purpose Equipment - Equipment that is unspared andextremely critical to the operation of a critical unit.

16. Single Acting - Liquid is discharged only during forward stroke ofthe piston.

17. Static Pressure - Gage pressure resulting from static liquidlevels.

18. Suction, Double - Liquid enters on both sides of impeller.

19. Suction, Single - Liquid enters on one side of impeller.

20. Throttling - Controlling flow rate by reducing cross-sectional flowarea, usually by partially closing a valve in the discharge piping.



21. Total Differential Head (TDH) - Pressure required in meters (feet)of head that the pump must produce. The head at the discharge pumpflange minus the head at suction flange.

22. Triplex - Pump with three plungers or pistons.

23. Variable Pressure Drop (Friction Losses) - Total pressure drop dueto frictional losses, excluding the control valve.

4. CLASSIFICATION OF PUMPS

4.1 Centrifugal Pumps

4. 1 .1 Brief Description

1. A centrifugal pump is one which generally uses an impellerwith fixed blades housed in a casing. The impeller ismounted on a rotating shaft and enclosed in a stationarycasing. Centrifugal force and subsequent increase inmomentum applied to liquid is used to transfer liquid fromthe inlet side to the outlet side of the pump. The headdeveloped by the pump is proportional to the square of theangular velocity of liquid at the tip of the impeller. Thehead is expressed in meters (feet) of liquid being pumped.

2. The impeller design and the shape of the casing determinehow liquid is accelerated though the pump. A truecentrifugal pump uses an impeller consisting of a seriesof blades set between two discs, giving a radial velocityof flow through the space between the discs. Otherimpeller designs may direct flow in both an axial and aradial direction or in an axial direction only. Pumps withthese impellers are known as mixed flow and axial flowpumps, respectively.

3. Axial flow pumps can realize very high efficiencies whenhandling large capacities at low heads, thus permittingselection of a much smaller and less expensive pump thanwould be required in the case of other centrifugal pumps.

4. Pump flow control usually is obtained by throttling thedischarge. The use of variable speed drive motors forcontrolling centrifugal pumps is increasing in thechemical industry. The advantage of this means of controlis that the control valve can usually be eliminated, thusreducing system pressure drop and power consumption.

5. Centrifugal pump sizes are designated using the followingformat:

(Discharge Dia. X Suction Dia. X Nominal Impeller Dia.)

Thus, a 3 X 6 X 9 centrifugal pump has a 76 mm (3 inch)diameter discharge, a 152 mm (6 inch) diameter suction,and a 230 mm (9 inch) nominal impeller. (The samedesignation is used in the SI or ISO and the U.S. systemof units.)

4. 1 .2 Advantages (See Table 1)

1. Supplies nearly constant head (depending on pump curve andflow rate).

2. No pulsation in flow.



3. Variable capacity with or without variable-speed drive.

4. Most will handle liquids containing some solids.

5. Good reliability.

6. Relatively low installed cost.

7. Can be operated at shutoff for short periods of timewithout damaging equipment.

8. Output can be throttled for control without damage andwith acceptable loss of efficiency.

4. 1 .3 Disadvantages (See Table 1)

1. Not suited for high viscosity liquids, maximum of 65centistokes [CS] (300 SSU).

2. Head developed is limited.

3. Limited ability to pump fluids containing vapors.

4. Most are not self-priming.

As pumped fluids increase in viscosity, centrifugal pumps loseefficiency. For fluids with viscosities greater than 20 CS (100SSU), a positive displacement pump should be investigated.Pumped fluids with viscosities of 45 CS (200 SSU) cause severeinefficiencies in centrifugal pumps. Fluids at or above 65 CS(300 SSU) shall require positive displacement pumps.

4. 1 .4 Types

1. General

Centrifugal pumps can be divided into six categories:

a. Overhung pumps.

b. Between bearings pumps.

c. Vertically suspended pumps.

d. Sealless pumps.

e. Submersible pumps.

f. Horizontal self-priming pumps.

2. Overhung Pumps

A pump with the impeller(s) cantilevered from its bearingassemblies is classified as an overhung pump. Impellersmay be cantilevered in the horizontal or vertical plane. While more than one impeller may be cantilevered, mostspecifications restrict horizontal pump designs to asingle cantilevered impeller and single suction. They maybe flexibly coupled or rigidly coupled. Horizontal pumpscan be foot mounted or centerline mounted. Vertical pumpsare in-line design, with or without integral high-speedgearboxes. Standard horizontal ASME B73.1M pumps andstandard vertical ASME B73.2M pumps are overhung pumps.

a. Foot Mounted - Pump is supported from underside ofits casing. Standard ASME pumps are foot mounteddesign. (See Figure 6.) These pumps are described indetail in ASME B73.1M, PIP RESP73H, and PIP REPAP001.



b. Centerline Mounted - Pump is supported along itshorizontal centerline. This arrangement allows pumpcasing to expand upward and downward from shaftcenterline as it is heated by pumped fluid. Thesepumps are used primarily in services above 150 °C(300 °F). (See Figure 6.) These pumps are described indetail in API 610 and GEMS P-2M.

c. Vertical In-Line - Pump shaft axis is in verticalplane and the suction and discharge nozzles have acommon centerline. Pump driver is generally mounteddirectly on the pump. There are four styles ofvertical in-line pumps (See Figure 7):

(1) Vertical coupled design with driver and pumpshafts connected by a solid coupling.

(2) Vertical motor shaft design with impellermounted on driver shaft.

(3) Vertical bearing housing design with separateupper pump bearing. The pump does not rely onthe motor bearing for radial support of pumpshaft.

(4) High speed (integral gear) design which usesintegral gearbox to increase speed of the pump.

These pumps are described in detail in ASME B73.2M,PIP RESP73V, PIP REPAP001, and/or API 610.

3. Between Bearings Pumps

A pump with the impeller(s) located between the bearingsis classified as a between bearings pump. The pump may besingle-stage (one impeller), two-stage, or multistage. Itcan be axially (horizontally) split or radially split.(See Figure 8.) These pumps are described in detail in API610 and GEMS P-2M.

a. Axially (Horizontally) Split - Pump case joint is inhorizontal plane.

b. Radially Split - Pump case joint is in radial planeor perpendicular to shaft axis. Pumps of this type aresometimes referred to as barrel pumps.

4. Vertically Suspended

A pump with the impeller(s) cantilevered vertically andthe suction nozzle typically submerged is classified as avertically suspended pump. There are six styles ofvertical suspended pumps: wet pit (diffuser) [verticalturbine], wet pit (volute) [vertical centrifugal], wet pit(axial flow) [propeller pumps], line shaft cantilever[sump pump], double casing (diffuser), and double casing(volute). Line shaft cantilever, double casing (diffuser),and double casing (volute) are the most common types ofpumps used for process fluids. (See Figure 9.) The pumpsare commonly used in low NPSH conditions where horizontalcentrifugal pumps will not function. These pumps aredescribed in detail in API 610 and GEMS P-2M.

a. Wet Pit (Diffuser) [Vertical Turbine] - Pumps usediffuser vanes in pump bowls. Typically used in wells



and below-grade collection services. Suction is frombelow grade pit or well. Flow of fluid follows axis ofpump shaft. (See Figure 10.)

b. Wet Pit (Volute) [Vertical Centrifugal] - Pumps usevolute casing design in pump bowls. Used in wells andbelow grade collection services. Suction is from belowgrade pit or well. Flow of fluid follows axis of pumpshaft.

c. Wet Pit (Axial Flow) [Propeller Pumps] - Pumps usepropeller-like impellers without bowls to pump fluidaxially up casing. Discharge follows axis of pumpshaft.

d. Line Shaft Cantilever [Sump Pump] - Pump typicallyuses a single impeller. Suction is from below gradepit. Discharge follows separate flow path fromimpeller.

e. Double Casing (Diffuser) or Double Casing (Volute) -Pump suction and discharge flanges are at grade.Basically, wet pit (diffuser or volute) pumps are putinside a can or casing to take suction on a processline located above grade.

5. Sealless Pumps

Sealless pumps are special pumps which do not requireshaft seals. There are two styles of sealless pumps:canned motor and magnetic drive. Sealless pumps are oftenused in services in which pumped fluid is extremelyhazardous and no leakage can be tolerated.

a. Canned Motor - Canned motor pumps are those in whichthe motor driver and the impeller are enclosedtogether as a unit. Since the design of these pumpsdoes not allow leakage of pumped fluid, they are onestyle of sealless pump. (See Figure 11.)

b. Magnetic Drive (Mag Drive) - Magnetic drive pumps arethose in which the pump impeller is driven by thedriver via a magnetic field. Since pumped fluid isconfined within a containment shell and no shaftpenetrates shell, no shaft seals are required. (SeeFigure 12.)

6. Submersible Pumps

Submersible pumps are designed for the pump and driver tobe completely surrounded by the pumped fluid. (See Figure13.)

7. Horizontal Self-Priming Pumps

Horizontal self-priming pumps are designed to create avacuum at the pump inlet. This enables the pump to “suck”fluid into its casing. The suction nozzle of the pump cantherefore be located above the level of liquid beingpumped. (See Figure 13.)



4.2 Positive Displacement Pumps

4. 2 .1 Description

1. Positive displacement pumps move a fixed volume of fluidduring each stroke/cycle by forcibly displacing liquidfrom the suction to the discharge. The pump capacity isdetermined by the effective volume of fluid displaced percycle multiplied by the number of cycles per unit of time.

2. Pump flow control is achieved by changing pump speed,adjusting the stroke length, or recirculating a variableportion of the flow from the pump discharge to the pumpsuction. Discharge is never throttled.

4. 2 .2 Advantages (See Table 1)

1. Constant flow at variable head.

2. Usually self-priming, depending on material being pumped.

3. Handles high viscosity liquids.

4. Develops high heads.

5. Handles vapor and gases in liquids.

6. Higher efficiencies than centrifugal pumps.

7. Better for handling emulsified fluids.

4. 2 .3 Disadvantages (See Table 1)

1. Requires variable speed driver or stroke adjustment tochange capacity of pump or bypass valve.

2. Usually pulsing flow.

3. Relief valves or rupture discs are normally required ondischarge.

4. Some types, such as reciprocating pumps, generally requiremore maintenance.

5. Generally require higher NPSH.

6. Generally more expensive than centrifugal pumps.

7. Generally require suction and discharge pulsationdampeners.

4. 2 .4 Types

1. General

Positive displacement pumps can be divided into threecategories: reciprocating, rotary, and metering.

2. Reciprocating Pumps

Reciprocating pumps create and displace a volume ofliquid, their “displacement volumes”, by action of areciprocating element. Liquid discharge pressure islimited only by strength of structural parts. Three formsof reciprocating elements are in use: piston, plunger, anddiaphragm. Reciprocating pumps are usually used in highhead, low flow, or metering applications. Reciprocatingpumps are specified if a high efficiency or exact flowrate conditions are required. Some typical examples ofthis type pump are gasifier charge pumps and inhibitor or



additive injection pumps. Suction and discharge flowdirections are controlled by valves. These pumps aredescribed in detail in API 674 and 675.

a. Piston Pumps

Piston pumps are used for low pressure light duty orintermittent service. They are less expensive thanplunger design but cannot handle gritty service. Theywork by a piston traveling through a cylinder whereinlet and outlet valves allow liquid in and out. Pumpsmay be single acting or double acting. (See Figure14.)

b. Packed Plunger Pumps

Plunger type pumps are used for high pressure heavyduty or continuous service. They are suitable forgritty and foreign material service. They are moreexpensive than the piston design. Plungers differ frompistons by having an external seal which limitsplungers to single acting but allows greater pressureand solids handling capability. (See Figure 14.)

c. Diaphragm Pumps

Diaphragm pumps displace liquid with flexiblediaphragm instead of a piston or plunger. (See Figure15.)

3. Rotary Pumps

Rotary pumps function with close clearances such that afixed volume of liquid is displaced with each revolutionof the internal element.

a. Gear Pump

Gear pumps consist of a driven gear and an idler gearmeshed such that liquid is squeezed out from betweenthe teeth. (See Figure 16.)

b. Lobe Pump

Lobe pumps are very similar to gear pumps except thatgears are replaced by multi-lobe impellers. Bothrotors are power driven and synchronized byinterconnection gears or a timing chain mountedexternally. (See Figure 16.)

c. Vane Pumps

Vane pumps use sliding or swinging vanes or flexibleblades on an eccentric rotor to force out liquid. (SeeFigure 16.)

d. Screw Pumps

Screw pumps use a helical-screw rotor in a casingdesigned such that the cavity created by the screwcloses at the discharge and forces liquid out at ahigher pressure. (See Figure 17.)

e. Progressive Cavity Pumps

Progressive cavity pumps use a single helical rotatingelement with a slightly eccentric motion inside aninternal double helical stator made of resilient



material. A sealed cavity is formed between the twoelements which progresses along length of statordisplacing a constant volume of liquid. (See Figure17.)

f. Peristaltic Pumps

Peristaltic pumps have a flexible tube pinched betweenthe lobes of a rotor and inside circumference of asolid housing. As the lobes rotate and pinch the tube,a cavity is formed between pinch points. The cavityprogresses from the inlet side of the pump to thedischarge side, displacing a constant volume of liquidwith each revolution. (See Figure 17.)

4. Metering Pumps

Metering pumps are generally small, with capacities in therange of 2 - 1660 l/hr (0.5 - 440 gal/hr). Since meteringand proportioning duties commonly call for differentvolumes to be delivered at different times, most meteringpumps are the variable-capacity type, usually variablestroke. Advantages and disadvantages of different types ofmetering pumps are shown in Table 2. Metering duties arenormally accomplished with special designs of piston-diaphragm pump heads where high accuracy is required.Plunger-type diaphragms may be used where higher pressuresare required. A bellows pump head may be used wheregreater capacity is required. Other positive displacementpumps are not excluded from metering service. Rotarypumps, for example, may be used for metering viscousfluids but cannot reproduce the accuracy of a truemetering pump, which is normally on the order of +1% orbetter.

5. SELECTION OF PUMPS

Figures 1 through 5 provide a decision tree guide to select pumps fortypical applications.

6. SELECTION OF PUMP DRIVERS

Table 3 provides information regarding selection of pump drivers.

7. GEARS

Table 4 provides information regarding selection of gears.

8. MECHANICAL SEALS

Pumps which require seals are typically provided with mechanical sealsas specified in API 610 or API 682.



9. COUPLINGS

1. Couplings are typically selected on the basis of the followingcriteria:

a. Misalignment tolerance.

b. Kilowatt (horsepower) [torque] requirements.

c. Accessibility of pump for maintenance.

2. Elastomeric or disc-pak spacer couplings are typically used.

3. Coupling type for ASME pumps shall be selected per PIP RESP73H.

4. Coupling guidelines for API pumps shall conform to API 610.



TABLE 1

SELECTION CRITERIA FOR CENTRIFUGAL, RECIPROCATING, AND ROTARY PUMPS

SelectionCriteria

CENTRIFUGAL RECIPROCATING ROTARY

AvoidsEmulsifyingthe Fluid

POOR GOOD GOOD

Reliability GOOD POOR FAIR

Self-Priming POOR (1) GOOD GOOD

HandlesAbrasives GOOD FAIR POOR (2)

HandlesLow NPSHA GOOD POOR (3) FAIR

HandlesEntrainedGas

FAIR FAIR GOOD

PumpsViscousFluids

POOR FAIR GOOD

Pumps LowViscosityFluids

GOOD GOOD POOR

EnergyEfficiency FAIR GOOD FAIR

InstalledCost GOOD FAIR GOOD

MaintenanceCost GOOD POOR FAIR

Notes:

1. Self-priming centrifugal designs are available.2. “Progressive cavity” rotary pumps handle abrasives.3. NPSHA on reciprocating pumps shall include allowance for acceleration

head.



TABLE 2

COMPARISON OF METERING PUMPS

Pump Type Advantage(s) Disadvantage(s)

MECHANICAL-DIAPHRAGM

- Least expensive.- Can handle most fluids.- Glandless.

- Accuracy not as good as plunger & piston- diaphragm pumps.- Diaphragm subject to fatigue failure.- Limited to low pressure deliveries.

PISTON-DIAPHRAGM - High accuracy.- Good diaphragm life.- Can handle most fluids.- Glandless.- Readily rendered in double-diaphragm form for fail-safe characteristics.

- Diaphragm may be subject to wear handling fluids including particulate matter.

ELECTRO-MAGNETICDRIVEN DIAPHRAGM

- Particularly suitable for micro-metering with precise pulse operation. - Glandless.

- Limited capacity.- More complex control system, (needs digital signal input).



TABLE 3

DRIVER SELECTION CRITERIA

DRIVER TYPE kW (HP) DUTYGEMS

SPECIFICATION

ELECTRIC MOTORS 132 (200) AND BELOW GENERAL PURPOSE L-2M

160 TO 1100 GENERAL PURPOSE L-3M

(250 TO 1500) SPECIAL PURPOSE L-5M

1100 (1500) AND ABOVE GENERAL PURPOSEAND

SPECIAL PURPOSE

L-5M

STEAM TURBINES GENERAL PURPOSE P-6M

SPECIAL PURPOSE P-7M



TABLE 4

GEAR SELECTION CRITERIA

kW (HP) DUTYGEMS

SPECIFICATION

BELOW 1500 (2000) GENERAL PURPOSE API 677

SPECIAL PURPOSE P-17M

1500 (2000) AND ABOVE SPECIAL PURPOSE P-17M































FIGURE 15DIAPHRAGM POSITIVE DISPLACEMENT PUMP

(SHOWN HERE AS DOUBLE DIAPHRAGM POSITIVE DISPLACEMENT PUMP)

Diaphragms





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Normas Texaco GEMS P-G-2 - Guide for Selection of Pumps