Water Brake (Hydraulic) Dynamometers. For trucking, off-road, military and mining equipment, Taylor Dynamometer’s water brake (also known as hydraulic) dynamometer systems offer the rugged operation and accuracy you need to ensure success.
http://www.taylordyno.com/products/engine-dynamometers/water-brake/
Measuring how much power you have. If you've got an engine or motor, you can use a different kind of dynamometer to measure how much torque (turning force), power, or speed it can produce. Here, the dynamometer acts as a variable load that the engine/motor drives.
http://www.explainthatstuff.com/how-dynamometers-work.html
A dyno that is coupled directly to an engine is known as an engine dyno. A dyno that can measure torque and power delivered by the power train of a vehicle directly from the drive wheel or wheels (without removing the engine from the frame of the vehicle), is known as a chassis dyno.
https://en.wikipedia.org/wiki/Dynamometer
Early hydraulic dynamometer, with dead-weight torque measurement. A dynamometer or dyno for short, is a device for measuring force, torque, or power. For example, the power produced by an engine, motor or other rotating prime mover can be calculated by simultaneously measuring torque and rotational speed (RPM).
https://en.wikipedia.org/wiki/Dynamometer
Schematic water brake on a dynamometer. A 4-minute ‘how-it-works video’ tutorial explaining how engine-dynamometer water-brake absorbers work. A water brake is a type of fluid coupling used to absorb mechanical energy and usually consists of a turbine or propeller mounted in an enclosure filled with water. As the turbine or propeller turns, mechanical energy is transferred to the water due to turbulence and friction.
https://en.wikipedia.org/wiki/Water_brake
Dynamometer Defined, Features, and Benfits. Dynamometer Defined. A dynamometer or dyno, is a test instrument used to measure torque and speed, which is used to calculate power of a device such as an engine, electric motor, pump, transmission, or generator/alternator.
http://dynesystems.com/what-is-a-dynamometer.htm
At the start of the test, the bike is warmed up, and then the technician initiates the dyno run. In the case of the Aprilia, he ran the bike at wide open throttle in fourth and fifth gears until it hit redline in each. It's a rather quick process. The force the bike outputs on the roller is torque. To get horsepower, the dyno uses that recorded number, RPM as a measure of time, and a number of other variables in a complex calculation (read: estimation) that spits out the magic horsepower number.
https://rideapart.com/articles/how-a-dyno-measures-horsepower
Build your own brake dyno. Brake/absorber dynos works by braking the engine and measuring the force (torque) it takes to brake it over the RPM range. Just leave the engine at wide open throttle and go through the RPM range by adjusting the braking force. The main challenge is the brake itself. The setup is quite simple once you have the brake.
http://yourdyno.com/brakeabsorber-dynos/
These days we measure horsepower with an extremely complex device known as a dynamometer, most commonly known as a dyno. The first step is to strap a bike down to the dyno; in this case we're testing an Aprilia RSV4 on an industry-standard Dynojet dyno.
https://rideapart.com/articles/how-a-dyno-measures-horsepower
Ideal for a wide range of markets, this style of dynamometer churns water inside the housing and transfers energy by momentum exchange and water shear. Generally speaking, the more water flowing through the dyno, the greater the braking force exerted on the device under test.
http://www.taylordyno.com/products/engine-dynamometers/water-brake/
what is a dyno brake
 A dyno brake is a device for measuring force, torque and power. A dyno brake is a device for measuring force, torque, or power.