Hydraulic dynamometers are machines that measure the power of an engine by using a cell filled with liquid to increase its load. Dynamometers, dynos or dynometers are used extensively in automotive and recreational vehicle applications because determining torque capacity, maximum rotary speed and maximum power absorption is important and valuable information for many drivers and riders.
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Hydraulic dynamometers are stationary and take measurements without requiring removal of the engine. These machines are also called water brake dynos because they use water or oil in the load cell. They are able to create different loads on the engine as well as maintain a steady RPM rate while testing, unlike inertia or chassis dynamometers. Because of this, these dynos are often used for troubleshooting tuning problems in the engine and determining if a part is not performing. In this way they contribute to a good overall power instead of a machine with a high horsepower peak. However, hydraulic dynos are more complicated than systems that use rolling barrels because of the way the dyno is attached. Also, the data requires more effort and knowledge to decipher because most hydraulic dynamometers are analog. Despite the few difficulties, these machines are still used in automotive, aircraft, aerospace, marine and industrial processes to measure chain or belt drives, gearboxes, fluid power systems, gas or diesel systems or transmissions in vehicles and motorcycles.
Hydraulic dynamometers couple the output shaft of an engine to a fan that rotates within a concentric enclosure. When the engine runs, the housing fills with a certain amount of water or other liquid. The more water in the housing, the more resistance it provides and the more load the engine feels. These kinds of dynos are able to accurately reproduce actual conditions in order to determine the engine's capabilities and shortcomings. As the fan spins, the blades impart kinetic energy to the water, and it whips around the housing, applying a force that is tangential to the housing radius. A data acquisition system uses sensors to measure force, the RPM of the input shaft, oil pressure, fuel pressure, fuel flow rate and other variables, which are often displayed on gauges though a computer setup if possible and more convenient. Because of the time and effort required to set up a hydraulic dyno, inertia dynamometers are more popular, though both kinds have advantages and drawbacks. Both inertia and hydraulic dynamometers are types of chassis dynos because the vehicle is kept intact during the test. Engine dynos require that the engine be removed so it can be tested. This provides a more accurate reading because the system does not experience the 15% to 20% energy loss due to friction through the drivetrain. It is also useful for testing motors before they are installed in the frame.
