API Reciprocating DisplacSteve Digby Pumpeteori

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


• 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.


Reciprocating metering/dosing pumps deliver a

controlled & accurate flow to predetermined points of a

process independent of pressure.


API 675 Metering Pump With

Diaphragm Pumphead

API 674 Reciprocating Triplex

Pump With Diaphragm

Pumpheads


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.


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


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


Installation Considerations & How to Avoid Problems


Flow Pattern of various Pumps Types

Simplex Pump

Duplex Pump

Triplex Pump

Centrifugal Pump


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.


Many Installations Are Designed On Smooth Flow

Conditions & Ignore Factors Such as:-


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:


•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.


• 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


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)



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!


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


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


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


Plunger Sealings

Non Return Valves


• 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


Pulsation Dampeners


Pulsation Dampener Affect

0 180 360

Overall Cost of Ownership


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


Documents

API Reciprocating DisplacSteve Digby Pumpeteori