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TeknaOffshore Pumps 2007
Pump Theory -API Reciprocating
Displacement Pumps.
Steve Digby
SPX Process Equipment Limited
Bran+Luebbe Operation U.K.
SPX Process Equipment
WCB-Flow Products
2003 2002
GD GD GD GD EngineeringEngineeringEngineeringEngineering
OFMOFMOFMOFMOilfield Fabricating & Machine
After Market & Field Services
2005 Plan
Employees 2585
Pump Theory API Reciprocating Displacement Pumps
Topics
• Reciprocating versus Rotary Pumps
• Basic Operation of Reciprocating Pumps
• API Specifications 674 & 675
• Suction Side Installation Considerations
• Overall Cost of Ownership
Pump Theory API Reciprocating Displacement Pumps
• API stands for American Petroleum Institute
• API 674 and 675 are widely used as an industrial standard for reciprocating displacement pumps.
• Mainly used in Petroleum, Chemical Processing, and Oil&Gas Industry.
• Describes and specifies constructional design, qualification criteria, and how pumps and documentation shall be executed.
Pump Theory API Reciprocating Displacement Pumps
Reciprocating metering/dosing pumps deliver a
controlled & accurate flow to predetermined points of a
process independent of pressure.
Pump Theory API Reciprocating Displacement Pumps
API 675 Metering Pump With
Diaphragm Pumphead
API 674 Reciprocating Triplex
Pump With Diaphragm
Pumpheads
Pump Theory API Reciprocating Displacement Pumps
Metering Pump Equation
V=A.h.n
V = theoretical Volumetric flow of the metering pump
A = plunger square area
h = stroke length
n = stroking speed (stroke frequency)
Positive Displacement PumpsReciprocating
Definition (in accordance with API Standard 674)
There is no actual definition in the standard other than
highlighting the difference between a Power Pump & Direct
Acting Pump.
Essentially these pumps transmit a predetermined mass
flow at medium to high pressure.
Pumps are normally configured in Triplex, Quintuplex and
Septuplex designs.
Positive Displacement PumpsControlled Volume
Definition (in accordance with API Standard 675)
“A controlled volume pump is a reciprocating pump in which precise volume control is provided by varying
effective stroke length”.
• Such pumps are also known as metering, proportioning,
chemical injection, dosing, or controlled volume pump.• These pumps deliver a controlled & accurate flow to
predetermined points of a process independent of pressure.
Pump Theory API Reciprocating Displacement Pumps
API Listing
1.5 Equipment offered is referring to German and European standards i.e. DIN, EN, IEC, ISO,....
2.2.5.1 Details of threading conform to ISO.
2.12.3 Unless proposed differently visual indication of capacity setting is shown as actual stroke
length.2.13.1.13 Bolts are calculated and selected in accordance with German pressure vessel code
(AD-Merkblätter).
3.1.7 Motors are flanged directly to the pump. Consequently, there is no need for jackscrews.
3.3 Metering pumps are suitable for mounting directly onto prepared concrete. Base plates are
therefore optional and can be quoted at additional cost.3.3.9 If not stated differently base plates will not be furnished with jackscrews.
3.4.3.2 If not stated differently single point terminal box for instrumentation is not included.
3.4.4.3 The gauges used for local diaphragm rupture indication have dials either 63 mm or 100
mm, depending on size of pumphead.
3.4.5 Electrical systems are not included unless expressly required and specifically quoted.
Typical Deviations to API 675
Pump Theory API Reciprocating Displacement Pumps
1
2 For: No. of motors required 1
3 Site Serial no. TBA
4 Remarks
5 Notes: O indicates information to be completed by Purchaser. � indicates information to be completed by manufacturer.
6 API standard 674 governs unless otherwise noted
7
OPERATING CONDITIONS (to be completed by purchaser)
8 Liquid (HC) Condensate Capacity @ PT (m³/h):
9 Pumping temperature (°C) PT: Maximum Note 2 Minimum Note 3Rated 5,3
10 Minimum -9 Discharge pressure (bar g):
11 Density @ PT (kg/m³): 569,8 Maximum Minimum Rated Note 4
12 Vapor pressure @ PT (bar): Suction pressure ( bar g):
13 Viscosity @ PT (cP): 0,16 Maximum Minimum Rated 17,8
14 Acceleration head (m) Note 1 Differential pressure (bar g):
15 NPSH available (m): 14,7 Maximum 19,2 Minimum Rated 16,2
Normal 19 Maximum 58
API Data Sheet – Purchaser Information
Pump Theory API Reciprocating Displacement Pumps
Installation Considerations & How to Avoid Problems
Pump Theory API Reciprocating Displacement Pumps
Flow Pattern of various Pumps Types
Simplex Pump
Duplex Pump
Triplex Pump
Centrifugal Pump
Pump Theory API Reciprocating Displacement Pumps
Suction Side• Insufficent NPSHA
• Pump Starvation
• Cavitation
What we are Trying to Avoid
Discharge Side• Insufficent Flow
• Over Pressure
• Pipe Hammer
In almost all cases of insufficient flow rate or frequent service
calls the pump will be blamed, not the system
General Poor Pump Operation
Only Recognised as Problems During Commissioning or
Initial Operation.
• Reciprocating Pumps Generate a Pulsating Flow
• ~3x Equivalent Smooth Flow.
• Line Losses Can be High.
• Crucial on Critical Applications i.e. Liquid Gases, High Temperature, Volatile Liquids.
Pump Theory API Reciprocating Displacement Pumps
Many Installations Are Designed On Smooth Flow
Conditions & Ignore Factors Such as:-
Pump Theory API Reciprocating Displacement Pumps
Bottom
dead
Center
100 % Capacity setting
60 % Capacity setting
Su
cti
on
Dis
ch
arg
e
Bottom
dead
Center
Top
dead
Center
Flow Pattern of a Single Head Pump
Two Major Factors That Can Adversely Affect The
Operation of Reciprocating Pumps Buy Are Often
Overlooked are:
Pump Theory API Reciprocating Displacement Pumps
•Friction LossesHigher Viscosity Applications
Pressure Required to ensure that the liquid flows continually in the
system during the maximum demanded flow volume.
Low Viscosity Application
•Mass Acceleration LossesPressure Required to cause the liquid to move at the beginning of
each plunger stroke
•Both Have a high impact on NPSHA .
•Only the higher of the two values is considered.
•On reciprocating pumps this is generally Mass Acceleration.
Pump Theory API Reciprocating Displacement Pumps
• Plunger or Piston Diameter.
• Stroke Length
• Internal Pipe Diameter & Overall Length.
• Pump Speed.
• Pump Configuration (Single or Multi Head)
Factors Affecting Mass Acceleration Pressure
Example.Single Head Pump 20mm Dia Plunger x 20 mm Stroke Length
Operating Speed 100 Strokes/Min Fitted To 8mm NB Pipe
Mass Acceleration Pressure = 0.84 m/m
Pipe Length = 10m
∆P = 8.4m or 0.84 Bar
Pump Theory API Reciprocating Displacement Pumps
Net positive suction head (NSPH) is the total inlet
pressure, stated in meters head minus the vapor
pressure of the liquid in meters
Net Positive Suction Head
What is a System ?(in terms of the issue “NPSH”)
A system is normally composed of:
• a pump
• a vessel from which the pump takes the liquid (suction vessel)
• piping between pump and suction vessel including valves, elbows, strainers, etc.
Suction vessel
Pump
p(abs)
or Habs
Hst
(Static
head)
L
(Length of suction piping)
d
(pipe inside diameter)
Pump Theory API Reciprocating Displacement Pumps
Pump Theory API Reciprocating Displacement Pumps
Mass Acceleration Forces
Simplex Pump
Duplex Pump
Triplex Pump
Centrifugal Pump
Net Positive Suction Head Available
NPSHA is a property of the system & determined
by the purchaser!
Pump Theory API Reciprocating Displacement Pumps
Net Positive Suction Head Required
NPSHR is a property of the pump and is the minimum
pressure required, measured at the suction flange, to
prevent cavitation.
For satisfactory pump operation NPSHA should always
exceed NPSHR by a minimum of *1 -2 m *(varies for different pump types and suppliers)
Head in suction vessel (above liquid level)
Head of vapor pressure Head of
friction losses
Head of mass acceleration losses
NPSHAStatic head
NPSHR
NPSH margin
Total headThe NPSH concept
Pump Theory API Reciprocating Displacement Pumps
How can NPSHA be calculated ?
NPSHA = H +Hst - Hvp - ΣΣΣΣHfr - Hma
The calculation is no more than determining the
difference between • positive heads
i.e. absolute head in suction vessel plus static head and
• negative heads (losses)i.e. head due to vapor pressure, friction and mass acceleration
Pump Theory API Reciprocating Displacement Pumps
Inadequate NPSHA Will Cause Cavitation Leading To:
• Erratic Performance
• Reduced Flow
• Erosion in The Plunger Packing Area and Non Return
Valves
• A Lot of Noise!!!
• Cost
Pump Theory API Reciprocating Displacement Pumps
Plunger Sealings
Non Return Valves
Pump Theory API Reciprocating Displacement Pumps
• Minimise the pipe length
• Maximise the bore diameter
• Minimise no of bend, tees and valves etc.
• Use of Pulsation Dampening Devices
• Increase Pressure (Booster Pump, Nitrogen
Blanket, Static Head etc).
• Use of a multi head pump.
• Adequate Pipe Supporting
Considerations to Maximise The NPSHA of the System
Pump Theory API Reciprocating Displacement Pumps
Pulsation Dampeners
Pump Theory API Reciprocating Displacement Pumps
Pulsation Dampener Affect
0 180 360
Overall Cost of Ownership
Pump Theory API Reciprocating Displacement Pumps
Process Fluid : MethanolFlowrate : 12m3/hr
298,500313,000Total costs after 3 years operation
148,50063,000Inc 1 set of plungers
Maintenance costs after 3 years operation
40,50018,000Annual maintenance costs
50 h x 150 = 7,50010 h x 150 = 1,500- labour costs
6 x 2,000 = 12,0006 x 2,000 =12,000- pump valves
None3 x 1,000 = 3,000- diaphragms
12 x 1,000 = 12,0003 x 500 = 1,500- plunger packing
6 x 3,000 = 18,000NoneAnnual Spare Use- plungers
150,000250,000Investment Cost
TriplexTriplexPump Type
Packed Plunger PumpDiaphragm Pump
Comments
Packing FrictionNecessary
Needs to be contained
~5% LowerNot Required
None
Energy costs
Lubrication of Plunger
Packing Leakage
Comparison of the investment and maintenance costs of a hydraulically
actuated diaphragm pump compared to a packed plunger pump
Process Pressure : 160 barOperating Hours : 8000/year
Thank you - Questions
Pump Theory API Reciprocating Displacement Pumps