Reciprocating Compressor Piston Speed

Introduction

Reciprocating Compressor Piston Speed is one of the important parameters in the selection of a Reciprocating compressor. In this article, we will see the importance of Reciprocating Compressor Piston Speed.

What is Piston Speed?

Normally Piston speed is defined as Average piston speed. Compressor manufacturers define average piston speed as the average linear speed at which the piston travels during one revolution of the crankshaft or two-stroke length.

Average piston speed is the product of reciprocating compressor stroke times operating speed, as per the below formula.

Now we will see the piston speed based on the compression cycle of the compressor, for a better understanding of piston speed.

 

As we see from the above figure, piston speed reaches a maximum value near the middle of the compression stroke and reaches zero at the end of strokes. Hence, we are using Average or Mean piston speed for reciprocating compressors.

Normally the average piston speed is 30 ~ 40% lower than the maximum piston speed.

Importance of Reciprocating Compressor Piston Speed

Piston Speed or Average piston speed is an important parameter to determine the wear and tear of the reciprocating compressor’s sliding and rubbing interfaces.

The main reason for the evaluation of piston speed by end users has based on the concept that lower piston speeds offer less wear and thus greater reliability of the compressor.

Higher piston speeds promote increased rates of wear on rider bands, piston rings, and rod packing.

During compressor selection, the EPC contractor or End User must compare the piston speed of the proposed reciprocating compressor model of various vendors.

Normally equipment manufacturer prefers higher piston speeds in order to keep the lower compressor size due to this compressor costs is reduced. During the comparison of various compressor models, ensure all the compressors have the same piston speed values.

For example, with the same capacity as the compressor, Vendor-1 proposes a higher piston speed and Vendor-2 proposes a lower piston speed compressor model than the size of Vendor-1 compressor is lower than the size of Vendor-2 compressor. Thereby the cost of Vendor-1 is much lower than that of vendor-2. But reliability point of view, Vendor-2 processed compressor is superior to vendor-1.

Although slower piston speeds result in larger cylinder sizes and increased rod loading, this disadvantage is usually overbalanced by reduced wear. Hence refer below table for recommended piston speed based on compressor speed.

 

Conclusions

The Piston speed mainly depends upon the operating speed of the reciprocating compressor.  The above table provided the piston speed range used by most compressor manufacturers.

API 618 / API 11P / ISO 13631 not clearly defined the piston speed values, it’s up to the manufacturer and end-user requirements.

To read about Reciprocating Compressor Distance Piece, Please Click Here

I hope this article is useful for you. Do you have any queries/feedback please mention them in the comment section.

Happy Learning!!