How does a Dynamometer work

[Great War truck]

I just came across a cracking picture of a dynamometer being used on a WW1 Holt 120 prime mover. My question is how does it work. Hang on, i will post the picture and then that should make it easier to explain.

 

Thanks

 

Tim (too)

[Great War truck]

Actually, I think that i might have asked this question before. So lets change it a little. What have been the most significant changes to the operation of dynamometers from WW1 to the present day, and how do they work? Discuss?

 

http://i30.photobucket.com/albums/c309/Greatwartruck/dyn.jpg[/img]

 

Tim (too)

[Richard Farrant]

Tim,

 

From the photo, I would assume they are measuring drawbar horsepower, by pulling heavy loads with a measuremnet of the pull being made from the drawbar of the tractor. It could be something like a large spring balance and relevant calculations taken from that. But.....I can just see what looks like a bike wheel behind the tractor and the guy nearest appears to have something in front of him. This would appear to be a a hydraulic type self-recording type of drawbar dyno. A hydraulic cylinder is attached to the tractor and the drawbar or chain is then attached to the test load. The cylinder is linked to the wheel and the recording unit (which I think is what the guy is holding). A large disc, similar to a modern tachograph, in the unit, records load and the rate of travel, to determine the horsepower.

 

When I was an apprentice agricultural engineer, we used a "water brake" dynamometer at Tech School, on the PTO of tractors to work out the PTO horsepower. These are something different to the above.

 

Richard

[Richard Farrant]

Actually, I think that i might have asked this question before. So lets change it a little. What have been the most significant changes to the operation of dynamometers from WW1 to the present day, and how do they work? Discuss?

 

 

 

Tim,

 

In the process of answering, you have added another posting. This type of measuring is the easiest way of checking a vehicle's pulling power. When manufacturers give what is called Brake Horse Power in their specs, it is taken from the engine's flywheel and quite often without the generator, fan or water pump being driven, in order that maximum power is measured. This, we used to do when rebuilding engines for military vehicles, on a Heenan and Froude water brake type dyno, which was used to bed in engines under variations of load before taking measurements of output, to ensure engines were up to standards.

[Degsy]

 

When I was an apprentice agricultural engineer, we used a "water brake" dynamometer at Tech School, on the PTO of tractors to work out the PTO horsepower. These are something different to the above.

 

Richard

 

 

Would this be in the days when a certain manufacturer always claimed they quoted PTO HP whilst their competitors quoted engine HP?

[Richard Farrant]

Would this be in the days when a certain manufacturer always claimed they quoted PTO HP whilst their competitors quoted engine HP?

 

 

Degsy,

 

Possibly..............?? Depends on thich manufacturues you are talking about ;-). The PTO water brake was a self contained unit that could be used to determine problems with tractors, or even bed in a rebuilt engine. Last saw one being used at the Great Dorset Steam Fair, by the tractor pulling boys.

 

Richard

[Degsy]

Richard, the memory is not what it was but I think the first mentioned was built in the Midlands (Coventry?) and others in Essex and Yorkshire.

[Richard Farrant]

Richard, the memory is not what it was but I think the first mentioned was built in the Midlands (Coventry?) and others in Essex and Yorkshire.

 

 

Ahh, well, I was with a MF distributor (Coventry built), and as far as I know, they always stated BHP from the engine, cannot speak for the lesser makes from Henry and David :whistle:

[Degsy]

The family have always had Fergie/ MF tractors (still do) the first being a Perkins engined Grey Fergie but when I was buying in the late sixties/early seventies I'm fairly sure I remember it as one of their selling points.

 

[Richard Farrant]

The family have always had Fergie/ MF tractors (still do) the first being a Perkins engined Grey Fergie but when I was buying in the late sixties/early seventies I'm fairly sure I remember it as one of their selling points.

 

 

 

Degsy,

 

Could be, but I just turned up some old Massey brochures from that period and of course, the Maximum power is BHP (taken from the engine flywheel) and that is what they were proclaiming. An example the 135 was 45.5 bhp, and 35 hp at the PTO. We always knew of it as a 45 horse tractor.

 

Sorry to Great War Truck, for deviating of his subject slightly

[Degsy]

Richard, I was just composing a message apologising to you when you posted. You are quite correct, I had been thinking about it and the claim was that they(MF) had a much higher percentage power at the pto for any given engine hp.

I am the guilty one for leading you astray and accordingly apologise to Tim, please bear with me Tim, with old age comes a wandering of the mind.

[Tony B]

Hey guys, I remember the water dynometer at college as well. As far as horsepower and tractor outputs go. The first set of comparative trials were done in Canada in Winnipeg in 1908 then in UK in 1910. But the US Nebraska trials set the standard. The vehicles are rated at Engine HP, drawbar HP and PTO horsepower. The draw bar power was apparently worked out using a trailer on firm dry ground and loaded till the vehicles could not start the trailer moving.

[Richard Farrant]

I just came across a cracking picture of a dynamometer being used on a WW1 Holt 120 prime mover. My question is how does it work. Hang on, i will post the picture and then that should make it easier to explain.

 

 

 

Tim,

 

There is another clue in the picture re. the test equipment, the building behind bears the name Herschel Mng. Co. Now, Clemens Herschel was a hydraulic engineer and was involved with dynamometers, such as being used in the picture.

 

Richard

[Great War truck]

Tim,

 

There is another clue in the picture re. the test equipment, the building behind bears the name Herschel Mng. Co. Now, Clemens Herschel was a hydraulic engineer and was involved with dynamometers, such as being used in the picture.

 

 

Thanks for all that info. Your responses have been most illuminating. I will now sit down and reread it all until it all sinks in.

 

I had noticed the name Herschel which seemed familiar but i could not think where i had seen it before, but that would make sense.

 

Thanks again

 

Tim (too)