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Compressor Loading Calculator

Rod Load, Frame Load & Operating Envelope

Compressor Loading Analysis
Calculate rod loads, frame loading percentage, volumetric efficiency, and capacity for reciprocating compressor cylinders using industry-standard methodology.

Compressor Data

lbs
Frame manufacturer rod load rating
throws
hp
rpm
inches

Cylinder Data

inches
inches
%
Total fixed clearance (both ends)

Operating Conditions

psia
psia
°F
relative to air
Cp/Cv
Natural gas: 1.24-1.34

Capacity Control

% additional
Additional clearance from fixed pockets

Loading Formulas

Parameter Formula
Head End AreaAHE = π/4 × bore²
Crank End AreaACE = π/4 × (bore² - rod²)
Compression LoadPd × AHE - Ps × ACE
Tension LoadPs × AHE - Pd × ACE
Volumetric Efficiency0.97 - 0.04 - Cl × ((Pd/Ps)1/k - 1)

Loading Notes

Rod Load Rating: Combined rod load (gas + inertia) must not exceed the frame manufacturer's rated rod load. Typical safety margin is 10-15% below rating.
Rod Reversal: Adequate rod reversal is required for crosshead pin bearing lubrication. Minimum reversal of 15% of maximum combined load is generally recommended.
Unloaders: Unloading one end changes the rod load balance and may affect rod reversal. Always verify loading after changing unloader configuration.

Frequently Asked Questions

What does a compressor loading analysis calculator determine?

It calculates rod loads, frame loading percentages, cylinder pressures, volumetric efficiency, and capacity for reciprocating compressors at specified operating conditions.

Why is rod load analysis important for reciprocating compressors?

Rod loads must stay within the frame rating to prevent structural damage. Both compression and tension rod loads must be checked, along with adequate rod reversal for bearing lubrication.

How do unloaders affect compressor loading?

Unloading the head end or crank end removes that end's contribution to compression work, reducing capacity and changing the rod load balance. This is used for capacity control and to manage loading at different operating pressures.