Large Water Pumps

GBH Enterprises, Ltd.

Engineering Design Guide:
GBHE-EDG-MAC-1507

Large Water Pumps

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Engineering Design Guide:

Large Water Pumps

CONTENTS

1

SCOPE
SECTION ONE: INTEGRATION OF PUMPS INTO THE PROCESS

2

PROPERTIES OF FLUID
2.1
2.2
2.3
2.4
2.5

Cooling Water
Brine
Estuary Water
Harbor Water
Oil-field water

3

CALCULATION OF DUTY

4

CHOICE OF TYPE AND NUMBER OF PUMPS
4.1
4.2
4.3

5

RECOMMENDED LINE DIAGRAM
5.1

6

Type of Pump
Points to Consider
Number of Pumps

Check List for Each Pump

RECOMMENDED LAYOUT


SECTION TWO: CONSTRUCTION FEATURES

7

HORIZONTAL, AXIALLY SPLIT CASING PUMPS
7.1
7.2
7.3
7.4
7.5
7.6
7.7
7.8
7.9
7.10
7.11
7.12
7.13
7.14

8

Pressure Casing
Bolting
Flanges and Connections
Rotating Elements
Wear Rings
Running Clearances
Mechanical Seals
Packed Glands
Bearings and Bearing Housings
Lubrication
Couplings
Guards
Baseplates
Flywheels

VERTICAL PUMPS
8.1
8.2
8.3
8.4
8.5
8.6
8.7
8.8
8.9
8.10
8.11
8.12

General
Pressure Casing
Bolting
Rotating Element
Packed Glands
Pump Head
Column Pipes
Line Shaft and Couplings
Reverse Rotation
Gearboxes


9

MATERIALS
9.1
9.2
9.3
9.4
9.5
9.6

10

DRIVERS
10.1

11

Castings
Casings
Impellers
Shafts
Shaft Sleeves
Bolts and Nuts

Electric Motor Drives

BIBLIOGRAPHY

APPENDICES:
A
B
C
D
E
F
G
H
I
J
K

COOLING WATER - EUROPEAN SITE
TIDAL RIVER ESTUARY
FLYWHEEL INERTIA FOR PRESSURE SURGE ABATEMENT
RESIN COATING OF CASINGS FOR WATER PUMPS
AREA RATIO METHOD
NOTES ON PUMP IMPELLERS CASTINGS
LIMIT ON SHAFT DIAMETER FOR HORIZONTAL PUMPS HAVING
ONE DOUBLE-ENTRY IMPELLER SUPPORTED BETWEEN BEARINGS
FORCES AND BENDING MOMENTS ON RISING MAIN ASSEMBLY
POWER COSTS
PUTATIVE COST COMPARISON SHEET
TECHNICAL COMPARISON SHEETS


FIGURES
2.1
2.2
3.1
3.2
3.3
3.5
4.1
4.2
5.1
6
7
8.1
8.2
8.3
8.4
9
10
11

VAPOR TEMPERATURE CURVES
DENSITY TEMPERATURE CURVES
TYPICAL HEAD OF PUMPS
TOTAL HEAD OF VERTICAL IMMERSED PUMP
TYPICAL TIDAL RIVER ESTUARY LEVELS
SUBMERGENCE LIMITS
TYPES OF PUMP
GUIDE TO PUMP TYPE AND SPEED
TYPICAL LINE DIAGRAM
GUIDE TO SUCTION PIPEWORK DESIGN
CASING AND IMPELLER DETAILS
DRY WELL AND WET WELL PUMP INSTALLATIONS
BELLMOUTH DIMENSIONS FOR VERTICAL INTAKES
MAXIMUM SPACING BETWEEN SHAFT GUIDE BUSHING
LINE SHAFT COUPLING
TYPICAL VOLUTE CASING
TYPICAL CASE WEAR RINGS
SEAL AREA

TABLES
1
2
3
4
5
6
7
8

LIQUID PROPERTIES SODIUM CHLORIDE (25% W/W)
LIQUID PROPERTIES SODIUM CHLORIDE (16.25% W/W)
RECOMMENDED CAST MATERIALS FOR USE IN THE PUMP
INDUSTRY

GRAPHS
1
2

GUIDE TO ROTOR INERTIA
LIMITS BETWEEN BEARINGS

DOCUMENTS REFERRED TO IN THIS ENGINEERING DEPARTMENT
DESIGN GUIDE

1

SCOPE

This Process Engineering Design Guide covers the following pumps and allied
systems, typical of petrochemical plants:
(a)

Cooling water circulating pumps

(b)

Brine transfer pumps

(c)

Sea and river water extraction pumps

(d)

Fire-fighting water pumps (excluding pumps on fire tenders)

Section One: covers the integration of pumps into the process and should be
read in conjunction with GBHE-EDG-MAC-1014.
Section Two: covers the construction features of large water pumps..

SECTION ONE – INTEGRATION OF PUMPS INTO THE PROCESS

2

PROPERTIES OF FLUID

2.1

Cooling Water
Cooling water will vary from plant to plant affected by the quality of water
treatment, process fluid ingress and local atmospheric conditions. See
typical analyses, Appendix A.

2.2

Brine
In general brine used will be saturated sodium chloride (NaCI) –for sample
analysis of fully saturated brine see Appendix B. Freezing point for fully
saturated brine is -21°C. (Reference Perry's Chemical Engineering
Handbook 4th Edition).

2.3

Estuary Water
Estuary water will vary mainly dependent upon the location, which in
general, is in a tidal river estuary. Typical analysis – see Appendix C


No account is taken of foreign bodies always present at river mouths or
the ever changing conditions which in the limit can vary from sea water to
river water. Freezing point varies from river water at QOC to sea water at 2.5°C (Reference Kemps Engineer's Year Book 1977).
2.4

Harbor Water
Do not assume that pump construction and materials suitable for sea
water are also suitable for harbor water. The latter may contain more
debris and be contaminated. Look for reference installations for each
individual case.

2.5

Oil-field Water
Brines from oil-fields may be contaminated by hydrogen sulfide and
therefore markedly more corrosive than sea water. High pressure injection
water is deaerated to inhibit bacterial growth and reduce corrosion (down
to the limit of measurement of about 25 ppb of oxygen). Such service is
beyond the scope of this Design Guide.

3

CALCULATION OF DUTY
Calculate the duty in accordance with GBHE-EDG-MAC-1014.
Brine pumps usually draw from a reservoir which has varying levels. The
differential head should be calculated on the maximum draw down level. A
minimum start level is required for vertical pumps to cover first stage
impeller - Fig 3.2.
Estuary water pumps situated in tidal river estuaries will be subjected to
density changes - use maximum density in the calculations. The lowest
spring tide level should be used in establishing the total differential head.
Fig 3.3.
Section A8 of GBHE-EDG-MAC-1014 is not sufficiently accurate when
applied to large capacity pump installations. Use the dimensions given in
Fig 3.5 to check the proposed layout. These values are based on M J
Prosser's The Hydraulic Design of Pump Sumps and Intakes, July 1977,
which is considered to supersede the Hydraulic Institute Standards, 1975,
pages 108 to 115, with an added margin drawn from existing proven
installations on several European plants.


If reduced submergence is required then model testing is essential.
For vertical bell mouths the intake should be more closely matched to the
normal flow lines to cater for the flow coming from behind the bellmouth.
Systems subject to pressure surge effects may be alleviated by fitting a
flywheel to increase the inertia/rundown time see; Appendix D. Special
motor starting arrangements will be required.

4

CHOICE OF TYPE AND NUMBER OF PUMPS

4. 1

Type of Pump
Section B of GBHE-EDG-MAC-1014 is supplemented by the table and
chart as a 'Guide to Pump Type and Speed'.
(a)

For line booster pumps for duties less than 100 l/s choose BS 4082
inline pump within the limits of GBHE-EDG-MAC-1014.

(b)

Choose a double-entry impeller, horizontal split casing pump up to
flows of 550 l/s. larger flows up to 4000 l/s can be achieved at the
expense of greater submergence and NPSH, necessitating a pit.


FIG 2.1

VAPOR TEMPERATURE CURVES


FIGURE 2.2

- DENSITY TEMPERATURE CURVE


SOOIUM CHLORIDE ( 25 % W/W )

SODIUM CHLORIDE ( 20 % W/W )

SODIUM CHLORIDE (16.25 % W/W)

SODIUM CHLORIDE ( 15 % W/W )

SODIUM CHLORIOE (10 % W/W)

SODIUM CHLORIDE (5 % W/W)

FIGURE 3.1

TYPICAL HEAD OF PUMP


FIGURE 3.2 TOTAL HEAD OF VERTICAL IMMERSED PUMP


FIGURE 3.3

TYPICAL TIDAL RIVER ESTUARY LEVELS


FIGURE 3.5

SUBMERGENCE LIMITS


(c)
(d)
(e)
(f)

(g)

4.2

Use single entry impeller, volute casing pump, vertical mounted
in dry wells for flows of 4000 to 6000 l/s.
Vertical column pump, wet sump line shaft may be chosen for flows up to
l5, 000 l/s.
Vertical pumps with a concrete volute become economical for flows above
6000 l/s.
Jet eductors are used in conjunction with a centrifugal pump to provide
suction lift to the centrifugal pump by diverting circa 50% of the pumped
rate around through an eductor located at the low water level. This in turn
induces 50% additional flow with the energy to lift and provide the
centrifugal pump with sufficient NPSH. The circuit requires a foot valve
and an initial priming system. The peak efficiency of the combination is
roughly that of the eductor. Standard commercial units are limited to low
flows (8 l/s), though pumps with 72 inch discharge nozzles have been
used in the USA (Reference Stepanoff - Centrifugal and Axial Flow
Pumps, 2nd Edition).
Two-stage pumps covered by Zone Y will more commonly be used in fire
fighting services where higher heads are required.

Points to Consider

When choosing the pump type the following points should be considered:
(a)
(b)

(c)
(d)

(e)

Vertical immersed pumps should be used on essential or auto start duties.
Pump wells/pits may be used for horizontal pump installations where
economically justifiable and should be provided with a reliable drainage
system with non-return facilities. To eliminate the possibility of flooding,
avoid using a well/pit, or at least, arrange any equipment liable to water
damage to be l50 mm above the finished ground level. Pits of 1 m depth
and greater are not permitted on plants handling flammable or toxic gas as
the area is liable to become the subject of a Chemical Works Regulation 7
entry certificate; also the Area Classification will be Zone 2 if not Zone l.
Pumps operating in series from the main cooling water main to boost
pressure for localized high pressure systems.
Power recovery from high pressure source let down to cooling water
return line pressure. This would take the form of a centrifugal pump
operating as a hydraulic turbine in accordance with GBHE-EDG-MAC1014, providing power via a double ended motor to the cooling water
pump.
Jet educt or/centrifugal pump combination should be used when the
suction lift is too great for an ordinary horizontal centrifugal pump or a selfpriming unit.


FIGURE 4.1

TYPES OF PUMP


Dry Well

4.3

Number of Pumps
(a) The reliability classification will in general be Class 4 as per GBHE-EDGMAC-1014, Appendix A. An analysis carried out on cooling water pumps
gave:


Consequently the first choice is one 100% duty main pump plus one
identical 100% standby.
(b) Main cooling water pumps are normally high powered; consequently the
power supply of the electric motors may have a step change in cost
corresponding to 415 Volts, 660 Volts, 3.3 kV and II kV steps in electricity
supply voltage.
(c)

Account should be taken of existing pumps in use on the same Works/Site
with the view of using common spares.


TABLE 7:


Note that the inlet NPSH often determines pump speed. The chart should then
be re-entered after converting the duty into the equivalent duty at the speed
given in the table, see GBHE-EDG-MAC-1014, Fig. B.2.3.2.


FIGURE 4.2:



5

RECOMMENDED LINE DIAGRAM (FIG 5.1)

5.1

Check List for Each Pump:

(a)

Permanent inlet strainer made from perforated plate BS 1669 Class A
12.5 mm. dia. holes: 3 mm. thick plate: the fine 20 mesh used for start up
on pumps with less than 6" inlets will be removed as soon as possible.

(b)

Suction isolation valve for horizontal pumps with flooded suction: the valve
should be anchored.

(c)

Pump casing drain valve if pump is not self-draining through pipework

(d)

Pump casing vent: this should be automatic on vertical pumps or pumps
on auto standby

(e)

Discharge pressure gauge

(f)

Non-return valve should be damped action with a short stroke, slam free
(i.e. Mannesmann, Demag or similar): the valve should be anchored to
withstand transient pressure load

(g)

Bypass for control or proving

(h)

Discharge isolation valve

(j)

Suction lines generally of 20" diameter or greater should be provided with
two Viking Johnson couplings for flexibility

(k)

initial coarse straining of sea/river water and open sumps require double
suction screens made from galvanized mild steel floor grating or mesh to
BS 4483, 049.

(l)

Sea and river estuaries water require a full width band screen or rotary
drum screen.

(m)

Any baffles in the sump should be made of stainless steel plate.


6

RECOMMENDED LAYOUT

For the rights and wrongs of suction pipework for horizontal pumps see Fig 6.


FIGURE 5.1

TYPICAL LINE DIAGRAM


FIGURE 6

GUIDE TO SUCTION PIPEWORK DESIGN


SECTION TWO: CONSTRUCTION FEATURES
7

HORIZONTAL, AXIALLY SPLIT CASING PUMPS

7.1

Pressure Casing
The casing should have the inlet and discharge nozzles in the lower half to
ensure maintenance can be carried out without disturbing the pipework.
The casing joint should only be allowed to overlap on the casing half
opposite to the direction of flow, see Fig 7.la.
Mis-matching of the two halves of the casing and failure to remove excess
metal from the slit joint can result in "spreading" of the volute and loss of
efficiency.
The casing joint should be metal to metal sealed with a jointing compound.
To reduce recirculation and axial hydraulic shuffling the casing walls
should be close to 25 mm and follow the line of the impeller shroud, see
Fig 7.lb.
When jacking screws are used to part joints one of the faces should be
relieved to prevent marring.
The casing surface finish should be in accordance with Appendix E.

7.2

Bolting
Tapped holes in the pressure parts are permitted providing that sufficient
metal in addition to the metal allowance for corrosion is left around and
below the bottom of the tapped holes to enable hole to be redrilled and
tapped to the next larger standard size.
Fastenings materials should have low galling and seizing tendency with
the mating material.


7.3

All flanges should be to BS 1560. Cast iron flanges should be flat faced for
full face gaskets. Flange sealing surfaces should be machined by a tool
rotating about the axis of the branch, the final cut being in the form of a
single spiral groove.

Surface texture is defined in relation to roughness comparison specimens
in accordance with BS 2634 Part 1.
Flanges should be spot faced on the back and should be designed for
through bolting.
All pumps should be provided with a vent connection. Pumps on auto start
should be fitted with an automatic air release valve.
Drain connections to completely empty the pump should be provided
unless the pump is self draining through the inlet or discharge piping.
Pressure gauge connections are not required on the pump casing.
7.4

Rotating Elements
The impeller diameter fitted for the rated duty should be capable of being
changed to give a 5% increase or a 20% reduction in head.
Impellers should be single piece castings.
Impellers should be positively located on the shaft. Keyed to prevent
circumferential movement. Lateral movement will be checked by a
shoulder on the shaft or lock nuts threaded to tighten by the
liquid drag on the impeller and mechanically locked.
If a double volute casing is used then there should be an odd number of
vanes on the impeller.


For large capacity, double entry impellers, the vanes should preferably be
on a staggered pitch on opposite sides of the centre line.
Check the Area Ratio see Appendix F.
Dimension checks on the impellers can be carried out in accordance with
Appendix G.
Reducing the generated head is permitted by machining impeller outside
diameter of Centrifugal/Francis Vane impellers, Fig 7.4a.
Mixed flow shrouded impellers head reduction is achieved by reducing the
average diameter of the outer and inner shrouds, cutting both diameters in
the same ratio. See Fig 7.4b.
Mixed flow open impellers/propellers head can be reduced by cutting the
trailing edge of the vane only, tapering from zero at the hub to maximum
at the outside diameter. The calculated reduction in head is based on the
reduction of tip lengths ratio not diameters. See Fig 7.4c.
Axial flow impellers generated head can be reduced by cutting down the
outside diameter but is rarely done in practice as it requires a new casing
on a liner. Varying the speed is the better solution.
Adjustment of the Q/H curve shape of a Centrifugal/Francis Vane impeller
is permitted by:
(a)

Underfiling the trailing edge of the vane. This can give a 3%
increase in head at BEP, the higher the speed the more
pronounced the effect. Fig 7.4d.

(b)

Overfiling the leading edge can give improved efficiency by
reducing the disturbance in the volute. Fig 7.4e.

Axial displacement greater than 2 mm and angular displacement greater
than 1° to the volute centre line will reduce pump efficiency.
Two stage pumps should have the impellers mounted back to back to give
balanced hydraulic thrust loadings.
The impellers should be dynamically balanced. The maximum total
residual out of balance should be to BS 5265 Part 1 G6.3.

Balance should be achieved firstly by reducing the vane thickness and
secondly by reducing the thickness of the shrouds. In neither case should
the thickness be reduced below the required minimum.
The shaft diameter and distance between shaft ends should be limited to
Zone B of Appendix H.
Shafts should be properly finished at the bearing surfaces and adequately
radiused at changes in diameter, corners of keyways etc. Vendor should
declare radius less than 5% of local radius of curvature.
Adequate provisions should be made for sleeve removal
Shafts should be provided with sleeves locked or clamped to the shaft.
The sleeve surface in contact with a moving seal component, or over
which such a component has to pass during assembly, should have a
surface finish of 0.2 to 0.4 µm Ra.
Shaft sleeves should be sealed at one end, and the shaft-sleeve assembly
(or nut) should extend beyond the outer face of the packing gland or the
seal end plate. Leakage between the shaft and the sleeve thus cannot be
confused with leakage through the stuffing box packing or the mechanical
seal faces.
Shafts should be machined and properly finished throughout their length
so that there is no more than 25 micron total indicated runout when
rotating element bearings are used. On the shaft sleeve assembled on the
shaft, complete with bearings, there should be no more than 51 micron
total indicated runout.
The diameter of shaft or shaft sleeve in contact with mechanical seals
should be a preferred metric diameter from the range:
24, 28, 33, 38, 43, 45, 50, 55, 60, 65, 70, 80, 90, 100, 110, 120, 130, 140,
150, 160, 180, 200.
A mechanical seal having direct contact with the shaft (i.e. no sleeve)
should be stationary relative to the shaft at the point of contact (e.g. a
bellows type seal).


Joints between impeller and shaft sleeve and impeller and nut should be
sealed by a gasket, trapped to prevent extrusion, or by lot rings to avoid
corrosion or the build-up of corrosion or decomposition products which
might complicate dismantling.
If screwed sleeves are unavoidable, the thread length should be not more
than 10 mm to reduce the chances of binding during maintenance.
Sleeve bore should be relieved for the major portion of its length but not
under the seal clamping position.
Any sleeves that directly clamp the impeller should be the same diameter
as the impeller hub at the intersection to ensure smooth entry flow.

7.5

Wear Rings

Renewable wear rings should be provided for the casing.
Tack welding is not permitted for the retention of wear rings. Locking
devices should not protrude into the wear allowance and should remain
effective when worn.
Casing wear rings which direct the leakage radially are preferred for
pumps with a suction specific speed greater than 0.4, to reduce the
unfavorable disturbance of the inlet flow into the eye of the impeller, see
Fig 7.5a.
The axial thrust balance arrangement should ensure that residual thrust
direction is unilateral over the operating capacity range. For this purpose
the nominal wear ring diameters may be different on opposite sides of a
double entry impeller.

7.6

Running Clearances

Clearances should be sufficient to assure dependable operation and
freedom from seizure. Design should be such as to avoid change of
running clearances due to uneven gasket compression.
For standard materials of rubbing pairs the clearances should not be less
than the values given in the following table.

7.7

Mechanical Seals
Select a rubber bellows type, e.g. Crane 502 and 521, Sized from the
range given in Clause 7.4. Inch sizes, type 4 and 5 are acceptable.
The use of seals with split carbon seats should be considered for large
seals where down time is critical and replacement of conventional seats
would involve a major strip down of the bearings housing and lube oil
system.
The seal face materials have traditionally been ni-resist and carbon 387A
(formerly BR171) but silicon carbide has proved successful on
contaminated water duties. For brine and seawater use 379A (formerly
BRMCM).
The seal should be backed up with a throttle bush or auxiliary packed
gland with a permanent clean water quench to prevent crystallization of
brine or seawater.
The gland plate should be designed to make metal to metal contact to
ensure accurate alignment of the seal faces.


The seal chamber should be provided with a vent (internal or external) to
permit complete venting of the chamber.

7.8

Packed Glands
Soft packed glands should be used for essential non-continuous
duties:
(a)

Fire water pumps

(b)

Storm water pumps

(c)

Sump pump-out pumps

A minimum of 3 turns of square packing will be used. Preferred sizes are
6, 8, 10, 12.5 and 15 mm square section.
Die formed rings are preferred to reduce maintenance effort.
A lantern ring with a clean water flush is preferred for brine and sea water
duties. The clean water flush pressure will be 1 bar above stuffing box
pressure.
The sleeve under the gland packing should be hard coated by fusion
welded surface deposits of nickel cobalt or nickel-boron-tungsten alloys
e.g. Stellite or Colomonoy.
Hard chromium electroplating is not acceptable.
The gland surface finish should be better than 0.4 micron Ra.
The packings should be replaceable without dismantling any other part of
the pump. The lantern ring may be the split design.

7.9

Bearings and lubrication should follow GBHE-EDS-MAC-1806 within its
limits, typically 500 kW. Outside these limits, bearings and lubrication
should follow the intent of GBHE-EDS-MAC-1806 simple, robust, self
contained design with an LID life in excess of 40,000 hrs (ISO R 281, Part
1).


Bearing housings should be axially split for the ease of maintenance and
equipped with a labyrinth type end seal/deflector where the shaft passes
through the housing. On oil lubricated bearing systems, lip seals may be
used for shaft sizes less than 60 mm.
Cooper Split bearings should not be used.
Bearing housings and components should be designed to minimize
contamination by moisture, dust and other foreign matter during running
and standby periods.
If water cooling is required it should be designed to cool the oil not the
bearing housing. The cooling system should be self draining to protect
against frost damage.

7.10

Lubrication
Lubrication shall be in accordance with GBHE-EDS-MAC-1806. If a
separate lube oil system is required it shall be in accordance with GBHEEDS-MAC-1806

7.11

Couplings
Couplings should be in accordance with GBHE-EDG-MAC-1101
"Engineering of Shaft Couplings".
A spacer of sufficient length will be provided to allow replacement of all
seal parts, sleeves and bearings without disturbing the pump or driver.
The pump coupling hub should be designed to be removed in situ.

7 .12 Guards
Should conform to BS S304 and withstand a force of 1000 N without
deforming to within 12 mm of moving parts.
Provisions for adequate ventilation to cool is required but split expanded
metal mesh should not be used.


The guard should be bolted in position and should be removable without
dismantling of other parts.
7.13

Baseplates
The baseplate should extend under the pump and driver.
All mounting pads should be fully machined flat and parallel to receive the
equipment. Corresponding surfaces should be in the same plane within
0.17 mm per meter of distance between pads, as machined to allow for
installation of shims 1.5 mm minimum thickness under the driver train.
When the pump vendor provides the driver, a set of stainless steel shim
packs 3.0 mm minimum thickness should be included. When the pump
vendor does not mount the driver, the pads for the driver should be
machined but not drilled, and shim packs should not be provided. All
shims should straddle hold-down bolts.
Baseplate and pump supports should be constructed and the pumping unit
mounted to minimize misalignment. The underside of fabricated
baseplates beneath the pump and driver supports should be welded in
order to reinforce cross-members and should have members shaped to
lock positively into the grout to resist upward movement of the baseplate.
All baseplates should be provided with at least one grouting opening
having a clear area of no less than 0.01 square meter and no dimension
less than 75 mm in each bulkhead section. These holes should be located
to permit filling the entire cavity under the baseplate without creating air
pockets. Vent holes 12.5 mm minimum size should be provided for each
bulkhead compartment. For dropped centre-trough baseplates, the holes
should be in the high section adjacent to the trough. Where practical,
holes should be accessible for grouting with the pump and driver installed.
Grout holes in the drip-pan area should have 12.5 mm raised-lip edges,
and if located in an area where liquids could impinge metallic grout hole
covers (16 gauge minimum thickness) should be provided.
Baseplates should be sufficiently stiff to maintain alignment without the
use of grout. Baseplates intended to be bolted down may be designed to
be adequate in the bolted down condition if their adequacy has been
demonstrated.


For electric motors over 75 kilowatts, alignment positioning screws should
be provided for each drive element to facilitate longitudinal and transverse
horizontal adjustments. The lugs holding these positioning screws should
be attached to the baseplate so that they do not interfere with the
installation or removal of the drive element.
Vertical leveling screwing spaced for stability should be provided on the
outside perimeter of the baseplate. These should be numerous enough to
carry the weight of the baseplate, pump, and driver without excessive
deflection, but in no case should fewer than six screws be provided.
Position as close as possible to HD bolts.
The height of the pump shaft centerline above the baseplate should be
minimized. Adequate clearance should be provided between the case
drain connection and the baseplate for installation of drain piping the same
size as the connection.
All pumps and drivers should be fully assembled and aligned within 50
micron total indicator reading in accordance with the cold alignment
diagram on their baseplate at the vendor's works. The baseplate should
be left free standing for this. Motor dowelling may be left until site
installation.
Support areas should be parallel within 0.05 mm when the base-plate is in
an unbolted condition.

7.14

Flywheels
From Appendix D it can be determined if a flywheel may be required to
prevent down surge. Checks should be made against the actual inertia of
the pump set before ordering.


8

VERTICAL PUMPS

8.1

General
Additional features required for vertical pumps are covered in the following
clauses.
Vertical shaft centrifugal pumps are either:(a)

(b)

8.2

Wet sump: suspended column type where the impeller and pump
bowl is immersed in the water and any major overhaul requires the
whole unit to be withdrawn, see Fig 8.la.
Dry sump: where all the parts of the pump are accessible in a dry
chamber, which allows maintenance to be carried out or impellers
changed to alter the duty. They can either be the suspended
column type see Fig 8.lb or the volute casing mixed flow, driven by
a remote driver, Fig 8.lc.

Pressure Casing
The bell mouth intakes should closely match the normal flow lines.
Elliptical cross-sectional dimensions are shown in Fig 8.2.
Concrete volute casing patterns are to be supplied by the pump vendor.

8.3

Bolting
To facilitate dismantling, internal bolting for vertical pumps should be of a
material fully resistant to corrosive attack by the fluid.

8.4

The pumps will have a vent connection fitted with an automatic air release
valve which will also act as a vacuum breaker.

8.5

Rotating Element
Collet fitting of the impellers to the shaft should not be used.


8.6

Packed Glands
Soft packing is preferred to mechanical seals.

8.7

The pump should have its own thrust bearing designed for an LIO life
greater than 40,000 hrs with a self-contain lubrication system. This
precludes the use of NEMA hollow shaft motors.
The design should permit replacement of the thrust bearing in situ without
moving the driver.
The line shaft bearings should be stainless steel shelled nitrite lined
(cutless rubber) lubricated by the pumped liquid, supported by spigoted
spiders, clamped between the flanges of the column pipes. The maximum
spacing between bearings is given in graph Fig 8.7.
Axial positioning of the shaft/impeller should be adjustable local to the
pump thrust bearing.

8.8

Pump Head
The pump will have a separate base mounting flange (sole plate) and this
should be grouted with epoxy grout.
A minimum of four alignment positioning screws should be provided to
align each element horizontally.
The head gear/support frame is to be designed to ensure that the pump
set is free from harmful torsional or lateral free or forced, steady or
transient vibrations. The natural frequency should be greater than 125% of
the motor speed.

8.9

Column Pipes
The column pipes should have cast integral flanges or fabricated with
machined faces and spigots to accurately align/position the bearing
spider.


Reversed bending moments due to the disturbing force at the impeller
should be taken into account, see Appendix J.

8.10

Line Shaft and Couplings
Cone couplings should be used and sealed against liquid ingress, see Fig
8.10a.

8.11

Reverse Rotation
If the system cannot be provided with a non return valve in the discharge
then a reverse rotation clutch should be used: Borg Warner, Morse,
Stuber Cluteh type RS/BF.
A time delay should be built into the motor started circuit to ensure that the
pump is not started against reverse flow.

8.12

Gearboxes
For concrete volute pumps where the speed is generally less than 8 rps
epicyclic gearbox in accordance with GBHE-EDS-MAC-1806 should be
used.


9

MATERIALS

9.1

Castings
Castings material should be in accordance with Table 1, taken from BS
DD 38.

9.2

Casings
Cooling water pump casings should be grey cast iron. Casings with 6"
branch sizes and greater should be coated in accordance with Appendix
E.
The objective of the coating is to avoid the reduction in pump performance
caused by corrosion roughening the volute surface.
Such corrosion occurs faster in stationary or standby pumps. The falloff in
efficiency is more marked for pumps where the rated flow is small and the
stage specific speed is low.
For a pump where Q = 450 l/s and Ns = 0.08 the long-term efficiency
reduction was 8%. For the same pump the hydraulic effect of applying the
coating was to raise the new pump efficiency by 2% over the untreated
casing. The same improvement was measured on Project A.2S68 Harland 6"/S" Uniglide Q = 104 l/s, Ns = 0.063. The on-site tests carried
out on a European Olefins Plant, cooling water pumps indicated a 1%
increase after coating. These are SPP pumps type BR24A with a flow of
IS60 l/s, Ns = 0.076.
These rises reflect the effect both of the treatment of the cast surfaces in
preparation for the coating and the smoothness of the coating itself.
For small pumps in essential but intermittent duty applications exemplified
by fire-fighting water supplies, the pump casing should be specified in an
inherently corrosion resistant material.
The coating technique is restricted to pumps with access to every wetted
surface.
Brine and sea water casings should be flake graphite austenitic cast iron
(ni-resist) or 'grey cast iron, coated in accordance with Appendix E.


Fire fighting water pumps should have casings of leaded gun metal.
If branch size greater than 6" then grey cast iron, coated in accordance
with Appendix E can be used.

9.3

Impellers
Cooling water impellers should be grey cast iron for acid free systems with
a suction specific speed of less than 0.4 and austenitic corrosion resisting
steel above this limit or if there is a possibility of acid contamination.
Brine and sea water impellers should have flake graphite austenitic cast
iron impellers for suction specific speeds of less than 0.4 and austenitic
corrosion resisting steel for greater suction specific speeds.
Fire fighting pump impellers should be leaded gun metal.

9.4

Shafts
Shafts for cooling water pumps should be to BS 970 - Part I, 080 M 40 or
better.
Brine and sea water pump shafts should be to BS 970 - Part 4, 416 S21 or
Monel.
The limit of a maximum of 1.5% chromium in steel shafts should not be
exceeded for pumps with white metal bearings with journal peripheral
speed 11 m/s.

9.5

Shaft Sleeves
Shaft sleeves material should be FV 520B stainless steel or BS 970
Part 4, 415 S21.

9.6

Bolts and Nuts
Brine and sea water pumps should have stainless steel studs/bolts to BS
970 Part 4 304 SIS or 321 S12 used with free machinery nuts material 303
S21 or 325 S21 with the alternative of bronze.


NB Aluminium bronze will not be used for any pump components.

10

DRIVERS

10.1

Electric Motor Drives
The pump should be direct driven.
The motor should be sized to cover end of curve conditions for pump sets
operating in parallel.
If the pump has a pressurized lube oil system then the motor bearings
should be supplied from the same system.
If the motor does not have its own thrust bearing then a limited end float
coupling should be used.
When a flywheel is provided the motor should be designed to cater for the
higher starting torque.
To achieve balance of the motor rotor, facilities should be provided at both
the drive and non drive ends.


TABLE 8

RECOMMENDED CAST MATERIALS FOR USE IN
THE PUMP INDUSTRY


FIGURE 7

CASING AND IMPELLER DETAILS


FIGURE 8.I DRY WELL AND WET WELL PUMP INSTALLATION


FIGURE 8.3 MAXIMUM SPACING BETWEEN SHAFT GUIDE BUSHING


FIGURE 8.2 BELLMOUTH DIMENSIONS FOR VERTICAL INTAKES


APPENDIX A
A. 1

European Site

A.1.1 Chromate Doped Systems
These include the large open evaporative systems and some smaller open
systems.

A.1.1 Nitrite Doped Systems
These include some coolers on Sulfuric Acid Plants and coolers on some
Methanol plants.

Note:
* Present in all corrosion inhibitors.
** Only present when microbiological control of system lost and NO2
oxidized to NO3 Not desired.

A. 1.3 Undoped Systems
This includes 'once-through' and recirculating systems. The recirculating
ones are so called 'Stability Index' controlled systems. No external
chemicals are added to prevent corrosion or scaling but a 'neutral' balance
is attempted by controlling make-up and blowdown. Such systems include
some of the smaller open systems, e.g. concentrated nitric acid, and the
coolers on Sulfuric Acid Plants.



A.3

CLOSED LOOP SYSTEM
On isolated Works, Plants and even items of equipment, self contained
closed loop systems are used. They require a head tank, fin fan cooler
and circulating pumps. To prevent the system from freezing the water is
treated with antifreeze (ethylene glycol with corrosion inhibitors). Avoid
using copper and copper alloys.


APPENDIX C
FLYWHEEL INERTIA FOR PRESSURE SURGE ABATEMENT
Pressure surges in long pipe lines are usually initiated from two sources:1

Rapid closure of valve in the delivery line, as covered in GBHE-EDGMAC-1014 Clause D3.

2

Loss of power from the driver causing down surge. The effects can be
limited by introducing a flywheel into the pumpset to increase the stored
kinetic energy available to maintain pumping for a short period.

The scope of this appendix is to guide the user in deciding:a

whether a flywheel is required

b

what order of size is required

The inertia of a modern pump and motor is relatively small and causes the
pumpset to reduce speed and head, rapidly. The addition of a flywheel of
sufficient inertia will extend the rundown time beyond the pipe line period of the
first reflection, preventing void formation in the delivery line by continuing to
generate pressure. Whilst a flywheel will prevent water hammer and valve slam it
has very little effect in reducing the peak pressures.


The initial indication of the pump set inertia available can be obtained from the
graph, which covers all types of shrouded impeller pumps with CACA or TEFC
electric motor drives.
The difference between 6 and 5 gives the approximate value of the moment of
inertia of the flywheel. If the difference is less than 20% of the total then do NOT
specify a flywheel but check further at the ordering stage with a detailed
investigation, involving the selected Vendor/ Vendors.


GRAPH I

GUIDE TO ROTOR INERTIA


APPENDIX D
D.1

RESIN COATING OF CASINGS FOR WATER PUMPS

SCOPE
This Appendix covers the requirements and the method of resin coating
pump casing internal surfaces of cast iron, axially split, single stage
pumps with branch sizes 6" nb and greater.

D.2

COATING
SAKAPHEN HD 60 EXTRA T is to be used.

D.3

PREPARATION OF CASTING
The casting should be prepared before shipping to the Suppliers Works.
Casings of pumps whose rated head is less than 40 m should have all
sharp edges and internal corners ground to a minimum radius of 3 rom.
This includes all the termination points such as the split joint, wear ring,
and flange bores, etc. For pumps with greater heads the minimum radius
at the split joint and flange bore should be 5 rom. See Figures 9 to 11.
All casting defects, protuberances, inclusions, etc, are to be removed so
that deviation from the desired profile gradient does not exceed 1 : 50.
This also applies to the horizontal split joint within the volute zone. See
Figure 9.
The volute cut water point and any vane trailing edges should have a
minimum radius of 5 mm.
All surfaces to be coated should be degreased, freed from plumbago or
foundry coatings by using the method laid down in BS 5493, Clause 14.2,
or by the use of vapor degreasing equipment.
Any machined surfaces that need protecting against grit blasting should
be clearly identified to the Supplier.
The pump manufacturer should ensure that a representative of the
Supplier inspects the casing before dispatch to the Supplier's works and
any preparation work that is not satisfactory should be remedied.


D.4

PREPARATION BY THE VENDOR BEFORE COATING
All identified machined surfaces are to be effectively masked against
blasting.
All surfaces to be coated shall be abrasive (grit) blasted clean to "Second
Quality" standard as laid down in BS 4232. (Swedish Standard SIS 05 09
00 Sa 2 1/t). The surface finish shall be better than 38 µ mRa.
After blasting the surfaces shall be cleaned from dust and abrasive
residue by dry air blast or vacuum.
Any cavities or fissures that remain shall be filled after blasting with epoxy
mortar (Devcon or Resocon) providing a margin to be finally ground back
to restore the correct profile.

D.5

COATING
The coating shall be applied in a dry, clean workshop. It is mandatory that
the first coat be applied within 4 hours of blasting - if not, the preparations
detailed in Clause D.4 should be repeated.
The coating should be applied in several coats with brush or spray to give
a minimum total thickness of 350 µm.
The coating work should be scheduled so that following coats are applied
before a previous coat is fully cured. (The coating is fully cured when the
test piece is unaffected by a solvent swab -use methyl isobutyl ketone or
acetone).
If it is shown that full curing has occurred then the gloss should be
removed before applying the next coat.

D.6

INSPECTION
Inspection should be carried out jointly by the pump manufacturer's
representative and the Inspection Department, or their appointed agent, at
the Supplier's workshop before dispatch.
Coating should not start until the Inspectors have approved all preparatory
work including mortar filling and a surface finish check against a
comparator tablet (for ground finish textures).


The Inspectors should witness the conductivity test carried out by the
Supplier over the whole coating using 9 Volt DC wet sponge method set to
signal when the resistance is less than 1 meg ohm This is a 'go' or 'no go'
test.
Spark test devices are forbidden.
Capacitance or similar measurement instruments, e.g. Elcometre, should
be used to obtain the thickness of the coating at random points chosen by
the Inspectors and at the edges of minimum radius.
D.7

RECTIFICATION OF FAULTS
The Supplier is responsible for the rectification of faults identified by the
Inspecting authority.
Patching of fault is permitted. The patch should extend the fault by 25 mm.
The gloss should be removed before the patch (in the same material as
originally used for the coating) is applied.
The repair should be subjected to inspection and a conductivity test.
FIGURE 9 TYPICAL VOLUTE CASING
FIGURE 10 TYPICAL CASE WEAR RINGS
FIGURE II SEAL AREA


APPENDIX E
E.1

AREA RATIO METHOD

Anderson conceived the parameter of the area ratio Y to relate the flow
conditions at the pump impeller outlet to those at the casing volute throat,
where:

Worster showed that the Q-H-E performance characteristics of a
centrifugal pump are chiefly determined by Y and not by the impeller blade
angle.
E.2

Following Thorne, the impeller outlet area is defined as:

The throat area ~ is the sum of the two corresponding areas for a double
volute or the Sum of the outlet areas between diffuser vanes defined as
for the impeller.


E.3

Intrinsic assumptions are that:
(a)

(b)

Impellers have the optimum number of vanes, given approximately
by 15. β where β' is the vane angle to the tangent, in radians.

(c)

E.4

High efficiency pumps are being sought for clean liquids of low
viscosity, so that vane incidence angles and shapes are properly
matched to the flow conditions.

Impeller inlet dimensions are not distorted to obtain the
exceptionally low NPSH capability corresponding to pump
operation at suction specific speed (Sn) values above 0.4.

Commercial and manufacturing considerations result in low specific speed
pumps having large area ratios, where

However, when pumps having a stable Q-H characteristic or a nonoverloading E-Q characteristic are required, then smaller values of Yare
needed where:

The efficiency does not vary strongly with Y but there is an advantage for
values of Y near unity.

REFERENCES
Centrifugal Pumps - An alternative theory, H H Anderson. Proc.I.Mech.E 1947
vol 157
The interaction performance of R C Worster. of impeller and volute a centrifugal
pump. BHRA Report RR.679.
Design by the Area Ratio Method in determining the 1960
E W Thorne. BPMA Sixth Tech Conf. Paper C2 1979


APPENDIX F

NOTES ON PUMP IMPELLERS CASTINGS

In order to obtain the quality of castings required the following should be agreed
with the pump vendor and drafted into the sub-order on the casting manufacturer.
(a)

Material Specification as agreed, taken from Table 8 of this Design Guide.
Typical mechanical and chemical material test certificates to DIN 50049 2.1 is the minimum requirement.

(b)

Dimensional tolerances for machining should be oversized by 2 to 4 mm
any final machining should have a surface finish better than 3.2 micron Ra
on wetted surfaces.
The width of the impeller vanes, at exist, should be within + 3% of the
design width or 3 mm whichever is the greater.
The thickness of the vane over its full length should be within + 12% of the
design thickness or 1 mm whichever is the greater.

(c)

Surfaces left as cast should have a surface finish better than 25 micron Ra
and the waviness better than 1 mm in 50 mm.

(d)

Any lumps caused by core shift should be removed and the correct inlet
angle retained. The vane tip should be rounded not knife edged, see
sketch.

(e)

The eye of the impeller should be fully machined. Any steps between the
cast and machined surfaces should be blended by grinding.


APPENDIX G
LIMIT ON SHAFT DIAMETER FOR HORIZONTAL PUMPS HAVING ONE
DOUBLE-ENTRY IMPELLER SUPPORTED BETWEEN BEARINGS
G. 1

FOREWORD
For a given Q-H duty, manufacturers offer pumps of different speed,
impeller size, shaft diameter and bearing span.
The speed is often fixed by NPSH considerations. This Appendix
considers the relation between shaft diameter and bearing span which
ensures long term reliable pumps operation when the flow varies over the
range 30-120% of the flow at the pump best efficiency point. Critical speed
phenomena are not considered.

G.2

PERTURBING FORCES
At the design point (BEP) the flows in the volute are fairly uniform and the
pressure distribution is uniform: consequently the steady-state radial load
applied to the shaft is very low.
At flows away from BEP the approximate radial load balance is disturbed,
with two effects:
(a)

The steady-state radial force increases

(b)

Low frequency cyclic radial forces become significant. Frequencies
corresponding to 10% running speed have been reported.

There are grounds for assuming that these perturbing forces relate to the
function:

All the pumps considered have had either single volutes or double-volute
casings, dependent upon size. The magnitude of the cyclic forces appears to be
roughly the same for both casing configurations, despite the reduction in steadystate force in double-volutes. This analysis does not apply to diffuser pumps.


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