Can I have a multi-stage reciprocating compressor?

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Discussion Overview

The discussion revolves around the design and functionality of a multi-stage reciprocating air compressor, specifically focusing on the arrangement of pistons and the implications for air compression at each stage. Participants explore theoretical aspects, practical considerations, and efficiency related to the compressor's design.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant describes a hypothetical arrangement of six piston-cylinder pairs, questioning whether this setup would yield more compressed air at each successive stage.
  • Another participant notes that common two-stage compressors typically have one piston larger than the other, suggesting that size differences are crucial for effective compression.
  • A participant argues that to increase compression in each stage, the volume must decrease with each step, proposing that the second stage should be smaller than the first.
  • One participant mentions that multiple cylinders could act as the first stage, reducing down to a single cylinder for the second stage, emphasizing the importance of reducing volumetric flow rate as pressure rises.
  • A participant highlights the efficiency of compound compressors, suggesting that using an inter-cooler and multiple bore sizes can enhance performance and pressure management.
  • Another participant references triple expansion steam engines as a parallel example, indicating a similar staged process in reverse.

Areas of Agreement / Disagreement

Participants express differing views on the design and efficiency of multi-stage compressors, with some agreeing on the necessity of reducing volume at each stage while others propose alternative configurations. The discussion remains unresolved regarding the optimal design for achieving increased compression.

Contextual Notes

Participants acknowledge the need for further exploration of gas laws and the specific reductions required for effective compression, indicating that assumptions about design and efficiency are not fully settled.

royp
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TL;DR
This is an enquiry about a multi-stage, reciprocating air compressor.
Hello,

This is an enquiry about a multi-stage, reciprocating air compressor. Imagine, there are 6 piston-cylinder-pair combination (numbered (P1, C1)...to (P6, C6) from the left); adjacent to each other. The arrangement is very similar to a 6-Cylinder internal combustion engine. Now, the pistons are moving in such a way that every alternate pistons are in sync. (and every adjacent pair of pistons are having a phase difference.) For instance, when piston P1 is pushing in, piston P2 is pulling out as they are out of phase and the compressed air from P1 will enter into P2 - (through the valve door) and so on.

My question is : with this arrangement, are we getting more compressed air at each successive stages in cylinders C1, C2, ..., C6?

Thanks in advance for your clarifications.
 
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The way you've described it, it won't increase compression in each subsequent stage. You need to be reducing volume with each step, so as AverageSupernova said, you'd need the second stage to be smaller than the first. Another option would be to have multiple cylinders acting as the first stage reducing down to a single cylinder for the second stage. Regardless though, the important factor is that the volumetric flow rate is reduced from each stage to the next as the pressure rises.
 
Averagesupernova, Cjl: Thank you both very much. So, with my improved understanding: If I want to achieve more compression, I need to make each successive stage smaller (in volume) than the previous one. The actual quantity (reduction) will be determined by gas laws etc. Am I correct?
 
The highest efficiency compound steam piston engines employed triple pressure reduction. Using compound compressors is also more efficient. One benefit is that an inter-cooler can be used. Another benefit is that the maximum pressure is not limited by the compression ratio of a single cylinder.

I expect you should consider a three phase pump so as to generate a continuous flow. For a compound pump that would require 6 cylinders with two different bore sizes. Only one medium pressure inter-cooler would be needed in the flow from the low pressure to the high pressure cylinder bank.
 
Thanks, Baluncore.
 
To see the process in reverse, look on the net for a triple expansion steam engine. For such a machine, the same steam is expanded through three stageds.
 
Many thanks for indicating a clever idea, Dr. D. Excellent brainstorming!
 

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