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2007 General Electric Company. All rights reserved.

Rod Drop

ReciprocatingCompressorsCondition Monitoring &Diagnostics

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Presentation Contents

Fundamentals

Instrument ettings

!etermining "rigger Angle

#ro$e Cali$ration

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Fundamentals

&ver time' so(t rider $ands)ear a)ay * especially innon+lu$ricated cylinders.

I( the e,cessive )ear is notdetected early enough' thepiston can contact thecylinder liner' causinge,pensive damage.

Cylinder Liner

Piston

Rider BandR

ing

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Piston DamageFundamentals

cung/ear

cung/ear

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Contact Sensors (Historic)Fundamentals

Fuse 1etal #lugpressuri3ed cham$er4

5oller 6alvepressuri3ed cham$er4

Contact sensors are installed asclose to the piston as possi$letypically on the pressurepacing gland4. "hey aremounted $elo) the piston rodand are activated ONLY)henthe rod contacts them )ithade8uate (orce.

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dd! Current Sensors(Modern)Fundamentals

Eddy current sensors are alsoinstalled as close to the pistonas possi$le typically on thepressure pacing gland4. "heycan $e mounted either a$ove or$elo) the piston rod' and cantae measurements at "NYtime.

Eddy Current#ro,imity #ro$e

(above or below rod)

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Rod Drop rend 'ampleFundamentals

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Measurement eometr!Fundamentals

P R O B E P O S I T I O N

C L

L 1 L 2

B 1

B 2

P I S T O N

M I D P O I N T

N E W

W O R N

A C T U A L R I D E R

B A N D W E A R

P I S T O N R O D L E N G T H

P R O B E

V I E W

P L A N E

( )

2

21

1

1

B

LL

B

L +=

( )

1

1212

L

BLLB

+=

#er the ;similartriangles

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"ssumptionsFundamentals

>. "he distance measurement made at the pressurepacing case changes in direct proportion to thechange in rider $and )ear assumes the similartriangles relationship is valid4.

2. Gravity is the predominant vertical (orce acting onthe piston and rod assem$ly.

%. 5od e, is negligi$le compared to the amount o( rider

$and )ear $eing measured.

-. &perating temperature o( the piston is relativelyconstant.

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deal Piston Rod #e*a$iorFundamentals

"his animation illustrates anideali3ed rod drop monitoringsituation.

"he rod drop measurementvaries as a gentle sine )aveshape over an entirerevolution o( the cransha(t.

5od+!rop+Ideal.gi(

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"ctual Piston Rod #e*a$iorFundamentals

"he animation sho)s rodposition test data collected(rom a highly+instrumentedcompressor.

animation4

#ro$e pair at piston rod pacing gland

% pro$e pairs installed (or testing
http://recipsim-stage1.exe/

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nstrument Settings

Installation dimensions => ?=24

&nce+per turn re(erencesignal

"rigger angle i( collectingone instantaneous sampleper cransha(t rotation4

"ransducer scale (actor

P R O B E P O S I T I O N

C L

L 1 L 2

B 1B 2

P I S T O N

M I D P O I N T

N E W

W O R N

A C T U A L R I D E R

B A N D W E A R

P I S T O N R O D L E N G T H

P R O B E

V I E W

P L A N E

Compressor1onitoring

Instruments

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Re+uired Measurementsnstrument Settings

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Signal Processingnstrument Settings

Average 6alue

1onitor processes thepro,imity transducer signalto create a single averagevalue over a complete stroeone (ull cransha(t rotation4.

!oes not re8uire cran angle

re(erence signal.

1ay $e ade8uate (or generaltrending o( rod drop values.

Instantaneous 6alue

1onitor collects a singlesample at a speciDed value o(cran angle ;trigger angle

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Determining rigger "ngle

election Guidelines

elect a value o( cran angle )here* the piston rod is in tension.

* the piston rod displacement is consistent atdierent compressor loads.

* the piston is close to the pro$e minimi3escorrection (actor4

ote "he ;de(ault< monitor setting (or"rigger Angle may not $e appropriate (oryour application.

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Rod Load $s, Cran- "ngleDetermining rigger "ngle

Full =oad Conditions #art =oad Conditions

240 240

"he piston rod is under compression at the de(ault trigger anglesetting 2-04.

tension

tensio

n

compression

compression

40 120 40 120

Ho)ever' it is under tension (or $oth (ull ? part loads $et)een-0 and >20.

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Rod Displacement $s, Cran-"ngle Determining rigger "ngle

40 120 40 120


#iston rod displacement is -9 mil (or $oth Full ? #art loads at 90cran angle.

60 60

tension

tension

tension

tension

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Rod Displacement(Oscilloscope)Determining rigger "ngle


360 360 360 360

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Pro.e Cali.ration

6eri(y pro$e cali$ration to the actual piston rodsur(ace to reduce errors caused $y the (ollo)ing(actors

* peciDc composition o( the piston rod alloy* ur(ace treatments' coatings' or contamination

* 5oundness o( the cylindrical piston rod sur(ace

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Piston Rod Material /ectsPro.e Cali.ration

Transduer!ut"ut#ignal($%C)

&tual Probe 'a" (ils)

24

22

20

1

16

14

12

10

6

4

2

0

0 10 20 30 40 *0 60 +0 0 ,0 100 110 120 130 140

->-0 teel"ungstenAluminum

Copper

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Micrometer 0itPro.e Cali.ration

1icrometer itaccommodates creating apro$e cali$ration curve (orthe actual piston rod.

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