03 fundamentals

7/27/2019 03 Fundamentals

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2

Discussion Points

• Basic Terminology

• Rod (Pin) Load

• Rod (Pin) Reversal



3

TERMINOLOGY (Jargon)

Gas Compressor Industry Language

Compression = The act of pressing or compacting

into a smaller space.



4

Terminology

R/Rc = ratio of compressionPs/P1 = suction pressure

Pd/P2 = discharge pressure

Ts/T1 = suction temperature

Td/T2 = discharge temperature

Ta = ambient temperature

Hp = horse power

HE = head end

CE = crank end

VE = volumetric efficiency

K = ratio of specific heats of a

particular natural gas - a thermaldynamic value



5

Terminology

Ratio of Compression (RC)

RC = Discharge Pressure(Pd)psig + 14.7 = ??? psia

Suction Pressure (Ps)psig + 14.7 = ??? psia

Note: Elevation or Barometric pressure must be taken

into account when figuring Rc.



6

Terminology

Finding Ratio of Compression (RC)Example 1: Ps = 200 psig, Pd = 600 psig

Rc = 600 psig + 14.7 = 614.7 psia = 2.863

200 psig + 14.7 = 214.7 psia

Example 2: Ps = 20 psig, Pd = 600 psig

Rc = 600psig + 14.7 = 614.7psia = 17.7

20psig + 14.7 = 34.7psia

Note: If we had not converted to psia the ratio

would have been 30:1.



7

Terminology

Finding Approximate HP Requirement: To find the HP required for a single

stage unit (example 1):

Approximating HP Formula using

Example #1

HP = 21 x Rc x S x Q

Where:HP = Horse Power

21 = Standard (Constant)

Rc = Ratio Of Compression

S = # of Stages

Q = Quantity in MMCFD

HP = 21 x 2.86 x 1 x 2 = 120.12 or 121



8

Terminology

Finding Approximate HP Requirement: To find the HP required for a two

stage unit (example 2):

Take the square root of the ratio found earlier:

Rc = 17.71 = 4.20

HP = 21 x Rc x S x Q

HP = 21 X 4.2 X 2 X 1HP = 176.4



9

Terminology

SA = Single Acting - The act of compressing

on one end of the compressor cylinder.

DA = Double Acting - The act of compressing

on both ends of the compressor

cylinder.

Tandem = Two compressor cylinders either bolted

together or cast as one casting, using a

common piston rod with two piston

sizes.



10

Terminology

Clearance Volume = The volume remaining in the compressor

cylinder at the end of the discharge

stroke. Normally expressed as a % of

piston displacement.

Displacement = Area of piston X length of stroke X # of

strokes per minute. For DA compressors,

the displacement on the CE is less thanthe HE due to the rod area. Normally

expressed in cubic feet per minute or

CFM.



11

Terminology

Capacity = (or flow rate) Volume of gas compressed

and delivered at specified conditions of

temperature & pressure measured at the

compressor inlet. Usually expressed as

volume/unit of time - cubic feet per minute

or cubic feet per day.

Approach = Refers to the heat exchanger design…

30°F approach means the cooler will cool

the gas to 130° when ambient

temperature is 100°F.



12

Terminology

Swept Volume = The volume swept by the piston during the forward

and/or backward stroke.

= Compressor speed is not a factor.

= Normally expressed in cubic inches and calculated asfollows:

Swept Volume HE = Area of Piston X Stroke in Inches

Swept Volume CE = (Area of Piston - Area of Rod) X Stroke in Inches

Total Swept Volume = (2 X Area of Piston - Area of Rod) X Stroke In Inches



13

Terminology

Total Swept Volume Example (DA):

6” Diameter x 7” Stroke 2.5” Piston Rod Diameter

Total Swept Volume = (2 X 28.274 - 4.909) X 7

= (56.548 - 4.909) X 7= 51.639 X 7

= 361.473 cu. In.



14

Terminology

Units of Measure:

PSI = pounds per square inch

PSIG = pounds per square inch gauge

PSIA = pounds per square inch absolute

= gauge + atmospheric pressure

MMCFD = million cubic feet per day

MMSCFD = million cubic feet per day @ thestandard conditions of 14.65psia & 60°F



15

Terminology

In-Hg = inches of mercury pressure

= can be a manometer or mercury filledgauge, used where pressures are low

& extreme accuracy is desired

= 1” Hg = .491 PSI

In-H2O = inches of water pressure

= usually a manometer filled with water

= used for measuring very low pressure

= 1/13.6 as heavy as mercury

13.6” of H2O = 1” of Hg = .491 PSI



16

Terminology

Temperature Scales:

Temperature =

A measure of molecular energy… the higher thetemperature the more molecular energy.

Degrees Fahrenheit (°F) =

Temperature scale where, at sea level, the freezing

point of water is 32° & the boiling point is 212°. The

distance between these two points is 180°.



17

Terminology

Temperature Scales:

Degrees Centigrade or Celsius (°C) =

A scale used worldwide which relates to the

metric system. At sea level, the freezing point of

pure water is 0° & the boiling point is 100°. The

distance between these two points is 100°.

Temperature range:

Centigrade = 100° = 5

Fahrenheit = 180° = 9



18

Terminology

Temperature Scales:

Converting from ° F to ° C expressed as follows:

° C = 5/9 X (° F - 32)

Example: Convert 100° F to ° C° C = 5/9 X (100 - 32)

= 5/9 X 68

= 37.8° C



19Separable Engine

V ConfigurationInline

Configuration

Horizontal Opposed Configuration

http://localhost/var/www/apps/conversion/tmp/Reference%20Material/Horizontal%204.ppt

http://localhost/var/www/apps/conversion/tmp/Reference%20Material/V-6.ppt

http://localhost/var/www/apps/conversion/tmp/Reference%20Material/In-Line%204.ppt



20

Separable

Compressor Frame

Click

Here

Terminology

http://localhost/var/www/apps/conversion/tmp/Reference%20Material/Compressor-Demo.mpe





21

Compressor

Engine

Coupled Separables



22

INTEGRAL ENGINE-

COMPRESSORS

Left Bank Right Bank

RH

LH

1

2

Flywheel

Sheave

3

Flywheel

2L

1L

3L

4L

5L

1R

2R

3R

4R

5R



23

Rod Load Definitions

• External Rod Load – The external rod load of a reciprocating compressor is a calculation considering

the unit in a static state. The calculation for deriving the ERL is:

– ERL = PD(HA) - PS(CA) where:

• PD = Discharge Pressure at the cylinder f lange

• PS = Suction Pressure at the cylinder flange

• HA = Head End surface area of the piston

• CA = Crank End surface area of the piston

• Internal Rod Load

– The internal rod load is often noted as the internal gas rod load of a reciprocating

compressor and the terms are synonymous. The IRL is a dynamic rod load

calculation based upon the internal gas pressures within the cylinder bore.

These gas pressures take into account the dynamic pressure drop characteristics

found across the valves and gas passages. The IRL is calculated through 360°

rotation of the crankshaft with the highest values being used.

• Net Rod Load

– The net rod load is considered a dynamic rod load rating. The NRL is the sum of

the IRL calculation and the inertia loads of the reciprocating weights. The NRL is

calculated through 360 ° rotation of the crankshaft with the highest values being

used.



24

2.5”

ERL Compression

Pd=814.7 PSIA Ps=214.7 PSIA

Area of piston in square inches times dischargepressure, minus area of piston, minus area of rodtimes suction pressure.

6”

= 28.274 x 814.7 - (28.274 - 4.909) x 214.7= 23,035 - (23.365 x 214.7)= 23.035 - 5016

= 18,019 #



25

2.5”

ERL Tension

Pd=814.7 PSIAPs=214.7 PSIA

Area of piston in square inches, minus area of rodtimes discharge pressure, minus area of the pistontimes suction pressure.

6”

= (28.274 - 4.909) x 814.7 - (28.274 x 214.7)= 23.365 x 814.7 - (28.274 x 214.7)= 19,035 - 6070

= 12,965 #



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Piston Rods Exceeding Rod Load



27Rod Reversal

Crank PinCrosshead Pin

Connecting Rod

Piston Rod

Crosshead

Oil

Oil



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• Data needed for CompressorSizing

– Operating Conditions – Gas properties

• Approximate HP per application

– Suction Pressure (PS)

– Discharge Pressure (Pd)

– Quantity of gas in MMCFD • Conditions Assumed:

– Suction Temp (TS) = 80°F

– Ambient Temp (Ta) = 100°F

– Discharge Temp (Td) required

approach = 20°F – Altitude = < 1500’

– Atmospheric Pressure = 14psi

– Specific Gravity = 0.64

– “N” value = 1.26

– Sweet Gas



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Questions?

03 fundamentals

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