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Horsepower, Indicated
Indicated horsepower (IHP) is the theoretical power developed by the gas inside a compressor’s cylinder or chamber during the compression process. It measures the internal work performed on the air, based purely on the pressure and volume changes that it undergoes during each cycle.
To calculate IHP, engineers use an indicator device to create a compressor indicator diagram, which plots the pressure inside the cylinder against the volume as the piston moves. The area enclosed by the loop on the diagram represents the net work done on the air during the complete compression cycle. IHP is then calculated using mean effective pressure (MEP), piston area, stroke length and revolutions per minute (RPM).
This theoretical power illustrates the thermodynamic efficiency of the compression process within the cylinder. It allows you to evaluate the effectiveness of several internal factors that impact productivity, like valve design and piston sealing. Measuring your machine’s IHP also allows you to pinpoint inefficiencies within the compression chamber.
Quincy Compressor designs and manufactures superior air compressor systems and equipment. Our engineers use IHP to ensure the internal compression process is as efficient as possible, minimizing the work needed to meet output requirements before any other mechanical losses come into play.
Here are some of the most frequently asked questions about indicated horsepower:
FAQs
IHP is mainly used as an engineering and design tool. This measurement is helpful in analyzing and optimizing the internal thermodynamic performance of air compressors. It measures the efficiency of the actual compression process and helps evaluate valve performance, assess the impact of clearance volumes and identify any inefficiencies.
IHP and BHP calculate the mechanical efficiency of an air compressor’s moving parts. IHP represents the pure thermodynamic work done to compress the air, demonstrating how efficiently the compressor is working on the air itself.
BHP is the mechanical power delivered by the compressor’s input shaft. This is the power that the engine supplies to turn the compressor mechanism. It shows how much mechanical power you need to supply to the compressor to achieve IHP, accounting for mechanical losses like friction, lubrication, pumping and other mechanical work.
A well-designed, well-maintained compressor minimizes these mechanical losses so that the higher percentage of brake horsepower translates directly into useful indicated horsepower.
IHP is commonly used for positive displacement compressors, specifically the reciprocating piston models. These machines have distinct cylinders and pistons that create clear pressure-volume cycles. IHP is a powerful tool for internal component analysis, enabling engineers to assess the overall effectiveness of the compression stroke, independent of external mechanical losses.
For rotary screw compressors, other metrics are typically used.
IHP is a fundamental parameter in compressor performance testing for reciprocating compressors. By analyzing IHP, Quincy’s engineering teams can identify internal losses, optimize valve timing and refine cylinder designs. This precision directly contributes to the development of highly efficient and reliable compressors, such as the QR-25 and QT lines, ensuring maximum internal work on the air with minimal losses.
