Competence at work for service and innovation

Reciprocating compressors

Design, Construction and Service

CST: range of activities

  • Feasibility Studies
  • Machinery Conceptual Design
  • Design of brand-new Machines
  • Design of complete Compressor Lines
  • Optimization and Modernization of Compressor lines
  • Manufacturing of Crankcases and Cylinders
  • Support to Production and Testing of new Machines

CST: Field of expertise

  • Power range from few kW to 30.000+ kW
  • Single stage or multi-stage with or without intercooling
  • “Lubricated” and “dry-lubricated” design (as a function of the service)
  • “Low” to “moderate” speed compressors operating at 300 to 750 rpm
  • High speed compressors operating typically at 750 to 1800 rpm
  • High pressure (up to 3.500 bar) compressors for Low Density Polyethylene Plants

CST’s team of highly experienced design engineers can develop the complete process from the conceptual phase to the detail design through the most advanced and integrated computing tools such as Virtual Prototyping, Computational Fluid-Dynamics (CFD) and Multiphysics.

Virtual Prototyping

Virtual Prototyping is a software-based engineering discipline which involves modelling a system, simulating and visualizing its behavior in real-world operating conditions, and tuning its design through an iterative process. The process begins with creating 3D models, combining the geometries of parts and related assemblies with their load conditions. Models are defined by a  commercial and a proprietary software for the simulation of kinematic and thermo-fluid dynamic behavior. It ends with a functional, structural and fatigue testing using linear and multiaxial nonlinear algorithms, depending on the specific part to be analyzed.


The ability to simulate multiple design interactions in a short amount of time results in a reduced prototyping cost. The time saved can be spent on other tasks related to product development like reliability, maintainability, and design for manufacturing, minimizing the time to market.
Virtual Prototyping involves:

  • Computer-aided design (CAD)
  • Computer-aided engineering (CAE)
  • Performance Software CST “Reciperf”
  • Finite Element Analysis (stress, temperature distribution, flow etc.)
  • Linear or Multi-Axial Fatigue.
  • Added modules that perform various other tasks, such as prototype manufacturing, product life cycle management, etc.

Virtual Prototyping allows to simulate complete machines and to apply loads as in a real physical object. Key design benefits:

  • Multiple tests possibility during the development of the project, thus real optimization of the design
  • Accurate evaluation of the contribution of various loads than what can be achieved on a real physical prototype
  • "See" things that could not be seen on a real prototype (virtual prototype is a full body model “instrumented” at all points)
  • Significant cost and time savings
  • Avoid (or drastically reduce) the need for a physical prototype

Fatigue Analysis

Stress analysis is not sufficient in the design of reciprocating machines, such as compressors, pumps, and engines. In fact, the criticality of these machines comes mainly from the large fluctuation of the loads which makes them subject to fatigue. Therefore, it is mandatory to take care of the stress fluctuation induced by the load variation and determine the fatigue safety factor by means of the appropriate method. Depending on the type of load variation, material and elastic or elastic-plastic situation, CST utilizes many different fatigue criteria including:

Compressor Cylinder Fuid-Dynamic Analysis some compressor components, such as the cylinders, in addition to the mechanical/fatigue design is necessary also a fluid dynamics check to enable the best energy management. CST has developed a dedicated software for cylinder fluid-dynamic optimization (CylOpt) that helps to define the best shape of the gas passages before undergoing a 3D Computational Fluid Dynamics (CFD) analysis.

Thanks to all these professional design tools, CST has successfully developed the complete design of several new machines, from the conceptual phase to the manufacturing specifications.

Fluid Structure Interaction

In some special cases, when it is necessary to investigate at deep the interaction between a fluid and a mobile mechanical component or when in presence of a two-phase fluid, CST special Fluid Structure Interaction software faces the duty of making the investigation.
The video aside shows the FSI done by CST to study a special case of movement of the valve rings during the opening time.


Modernization & Upgrades

CST machine design know-how applies also for improvement of existing reciprocating compressors, by eliminating recurrent problems, helping users to increase the reliability of their plants, reducing operating costs.

Some Examples of the CST Design Activity
for Reciprocating Compressors:

CST Machine Design capability for Reciprocating Compressors, typical applications:

  • Compressor Frame design including Crank-mechanism, crankcase and all their components
  • Compressor Cylinder design for all main application (Process, Low temperature, High pressure LDPE, CNG, Hydrogen, etc)

Some examples of projects developed by CST


Machine design is done by CST engineers through virtual prototyping technique which allows to take into account all forces and constraints as in a physical prototype to reproduce the actual operating conditions


The crankshaft is designed through a linear elastic FEM analysis and fatigue evaluation by Dang Van fatigue criterion.


CST was requested by a customer to revamp an old reciprocating compressor. The connecting rod was reviewed to debottleneck the weak points.


The connecting rod tie bolts are designed by CST through a linear elastic FEM analysis with fatigue evaluation by the multi-axial non proportional Brown Miller criterion.


One of the most critical gas passages in the reciprocating compressors is the "valve pocket". CST designs those passages by the proprietary software Cylopt-Mono, followed in the most challenging cases by a CFD analysis


A case of a full CFD analysis done by CST for the design of the gas passages of the whole cvlinder. This study was done to fine-tune the first selection done with the proprietary software Cylopt-Mono.


Large bore cylinders face uneven pressure distribution on the piston faces when they are close to the dead centers. CST analyses these cases by a software of Fluid-Structure-Interaction.


A typical double-acting cryogenic cylinder designed and manufactured by CST utilizing special materials suitable for very low temperature.


Main threaded connections need a detailed analysis to assess the infinite fatigue life of the relevant components. For the connection of the piston rod to the crosshead CST simulates the real threads going beyond the normal solid representation of the connection.


Balancing reciprocating masses is of the utmost importance to reduce compressor vibration. CST gives particular care to the design of ballasts, counterweights, opposed cylinder line offset and foundation bolts.


The best insurance for a good operation of the bolting subject to fluctuating loads is a correct preload and an adequate elasticity of the connection. CST designs the connections and supplies the tightening system to avoid uncertainties of the preload. 


To avoid dangerous vibrations the bare compressor shall generate the minimum of excitations and to constitute a stiff connection for the piping system. CST, thanks to its multi-disciplinarity, can take care of all these aspects.

Compressor manufacturing, assembling and testing

CST and its qualified partners have the capability to manufacture all components, assemble and test compressors.
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Reconditioning and upgrade of existing compressors

CST service is not limited to the design and manufacturing of new units but covers also its customer for repairs instructions, parts reverse engineering and provision, modification, and optimization of existing compressors to meet new plant requirements, different gas condition and improve compressor performance.
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