Editing Dynamometer (section)

===Water brake-type absorber===
[[File:Tech-Talk_Animation_on_How_Water-Brakes_Work.webm|thumb|A  4-minute ‘how-it-works video’ tutorial explaining how engine-dynamometer water-brake absorbers work.]]

The hydraulic dynamometer (also referred to as the [[water brake]] absorber)<ref>{{Cite web |date=2017-12-24 |title=Hydraulic Dynamometers - Froude |url=https://froudedyno.com/products/dynamometers/standard-hydraulic-dynamometers-f-type |access-date=2023-09-01 |website=Froude {{!}} Dynamometer Manufacturer |language=en-gb}}</ref> was invented by British engineer [[William Froude]] in 1877 in response to a request by the [[British Admiralty|Admiralty]] to produce a machine capable of absorbing and measuring the power of large naval engines.<ref>{{cite web |title=History {{!}} About Us |url=https://froudedyno.com/about-us/history |url-status= |archive-url= |archive-date= |access-date=1 September 2023 |publisher=Froude Hoffmann}}</ref> Water brake absorbers are relatively common today. They are noted for their high power capability, small size, light weight, and relatively low manufacturing costs as compared to other, quicker reacting, "power absorber" types.

Their drawbacks are that they can take a relatively long period of time to "stabilize" their load amount, and that they require a constant supply of water to the "water brake housing" for cooling. Environmental regulations may prohibit "flow through" water, in which case large water tanks are installed to prevent contaminated water from entering the environment.

The schematic shows the most common type of water brake, known as the "variable level" type. Water is added until the engine is held at a steady RPM against the load, with the water then kept at that level and replaced by constant draining and refilling (which is needed to carry away the heat created by absorbing the horsepower). The housing attempts to rotate in response to the torque produced, but is restrained by the scale or torque metering cell that measures the torque.

[[Image:Dyno schematic.svg|frame|center|This schematic shows a water brake, which is actually a fluid coupling with a housing restrained from rotating&mdash;similar to a water pump with no outlet.]]