Put to the Test: Using a Prony Break

Doug Wise built his own Prony brake to test engine horsepower for steam engines and tractors.

| January 2008

  • Checkingfullthrottle.jpg
    This 1916 Minneapolis is carrying the mail, running at near full throttle as the Prony brake measures its horsepower.
  • checktachometer-1.jpg
    The 1916 Minneapolis belted to the Prony brake.
  • checktachometer.jpg
    Lester and Judy Wise check tachometer readings as Doug Wise (right) increases scale pressure.
  • Illinois.jpg

  • checktachometer-2.jpg
    Doug checks the small belts on the Prony. When not working on the brake, he spends time with his collection, which includes a variety of tractors and a 1913 Rumely steamer.
  • checktachometer-3.jpg
    A back view of the scale and drum. Most of the Prony brakes Doug has seen were permanent show installations, and all were home-built.

  • Checkingfullthrottle.jpg
  • checktachometer-1.jpg
  • checktachometer.jpg
  • Illinois.jpg
  • checktachometer-2.jpg
  • checktachometer-3.jpg

Ever wonder if the horsepower listed for your tractor or steamer is correct? If you had a Prony brake, you could find out in no time.

Don't try to find a Prony brake at your local farm implement store. Such devices are not produced commercially, says Doug Wise of Cedarville, Ill. But if you're mechanically inclined, you can build your own way to test engine horsepower - like he did.

Invented in 1821 by French engineer and mathematician Gaspard de Prony, the Prony brake - actually an early dynamometer - measures the torque produced by an engine. In fact, the term "brake horsepower" derives from this method of torque measurement. de Prony built the machine to test water wheels, according to Doug's mother, Judy Wise, who has delved into the history of de Prony and his invention.

With de Prony's device, measurement is made by wrapping a belt around the engine's output shaft and measuring the force transferred to the belt through friction. Friction is increased by tightening the belt until the shaft's rotation frequency is reduced. Additional engine power can be applied until the engine's limit is reached.



Various methods can be used to measure the force applied to the brake. For the belt method it is common to use a pair of spring balances and apply a pretension to the belt. When the shaft rotates, one balance will demonstrate an increased tension while the other shows reduced tension. Factor in the shaft diameter, and the difference is a measure of the torque.

In another approach, clamp a lever to the shaft and measure using a single balance. The torque is then related to the lever length, shaft diameter and measured force.



SUBSCRIBE TO FARM COLLECTOR TODAY!

Farm Collector April 16Farm Collector is a monthly magazine focusing on antique tractors and all kinds of antique farm equipment. If it's old and from the farm, we're interested in it!

Save Even More Money with our SQUARE-DEAL Plan!

Pay now with a credit card and take advantage of our SQUARE-DEAL automatic renewal savings plan. You'll get 12 issues of Farm Collector for only $24.95 (USA only).

Or, Bill Me Later and send me one year of Farm Collector for just $29.95.




Facebook Pinterest YouTube

Classifieds