Turbomachinery specifications

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Below is a part of a paper, "Turbomachinery Specifications", presented by John Housman, chief engineer in equipment planning and engineering department of the American Oil Company, at the first ever Turbomachinery Symposium in 1972 in Houston.

Housman talks about basic questions that a purchaser has to answer so that he or she can specify a compressor-driver system. It seems these questions are still the starting point today.

(An Elliott turbomachinery compressor)

Purchaser decisions

Regardless of the amount of detail  contained  in  general specifications, API or otherwise, many  decisions must be made by the purchaser for each specific job. Some of these can be made in advance  and  included in the General specifications whereas others are strictly job oriented. Table 1 presents a  listing of the usual purchaser decision items that should be resolved to finalize a specific job specification.

Table 1

Purchaser decisions


  • Layout

Grade or mezzanine mounted ; nozzle orientation; oil system (s) location; accessibility requirements.

  • Arrangement

Single or parallel units; direct connected or geared; allowable number of connected casings; baseplate or soleplate mounting; maintenance handling.

  • Environment

Indoor, shelter, or outdoor; degree of dust, rain, etc.; winterization requirements ; temperature range.

  • Type of Compressor

Centrifugal, axial, rotary or reciprocating; speed limitations if any; uncooled or intercooled.

  • Type of Driver

Steam turbine, gas turbine, or electric motor; geared or direct connected.


  • Operating

Normal and rated conditions; operational variations ; projected run length; gas composition (s); corrosiveness of gas.

  • Casing

Horizontally or vertically split; steel, ductile iron, cast iron or other material; cast, forged, or fabricated ; vent and drain requirements.

  • Impellers

Semi-open or closed; material; welded, riveted, or milled; hardness limitation.

  • Seals

Labyrinth, contact, or liquid film (bushing), separate seal oil system or common with lube systems; type of labyrinth seal auxiliary system.

  • Couplings

Dry membrane type or lubricated gear type ; grease packed or continuous lube ; close coupled or spacer.

  • Lube Oil System

Single or multiple systems ; pump and driver types and arrangement; number of filters and degree of filtration; type and extent of instrumentation and control; single or twin coolers; supply water specifications and allowable temperature rise.

  • Seal Oil System

Integral with or separate  from lube oil system; overhead seal oil tanks or differential pressure controller ; float operated drainers or collecting pots with control valves; plus same items as for lube oil system.

  • Basic Control Scheme

Pressure or flow control; control by speed, suction throttling, or bypass integral inlet guide vanes or external throttle valve.

  • Instrumentation

Hydraulic, pneumatic or electronic control; panel or local mounted instruments; coverage and quality of instrumentation; vibration monitoring equipment requirements.

  • Testing

API basic test requirements only or additional testing; closed loop performance, driver, and/or auxiliary equipment test requirements.

  • Drawing and data requirements

For record only or for approval; number of copies or timing requirements.

  • Steam Turbine Drivers

General or Special purpose; steam conditions including variations; operating horsepower and speed range requirements; single or multivalve construction; carbon ring or labyrinth packing; integral or built-up rotors; type and degree of instrumentation.

  • Gas Turbine Drivers

Type of starting and/or helper unit; starting torque requirements; single or two shaft unit; manual semiautomatic, or automatic start-up; type and quality of inlet filter and silencer; exhaust gas recovery facilities; type and degree of instrumentation.

  • Electric Motor Driver

Electrical characteristics; type of motor enclosure required; starting torque characteristi cs and requirements; instrumentation requirements.

  • Gear Units

Hardness, noise level, and service factor limitations; instrumentation requirements.