DYNO explained?

41B-boy

Member
Location
Chehalis, WA
G'day all,
I notice there is a dyno for sale, and it reminded me that I've wanted to ask a knowledgeable person to offer a brief thumbnail sketch of how they work...
I've never seen one up close and personal like, and would appreciate a brief edumacation. Yes, I realize it's pretty obvious, but take a shot anyway.

Thanks, Bob
 
The ones I have been around used water or oil as media to force thru orifice witch useing calibrated gauge gave reading witch was translated to HP.
 
Here?s a more complicated explanation -

The M&W Gear Company?s PTO dynamometers are hydraulic devices. The PTO spins a big hydraulic pump and it pumps oil within the dynamometer through an adjustable orifice (a valve opened and closed by a hand wheel). As the valve is slowly closed, oil pressure builds, but the flow rate remains constant as long as the RPM remains constant.

The horsepower required to force a specific oil flow past an orifice at a specific pressure can be determined by the formula:

HP = Flow rate (in GPM) x Pressure (in PSI) / 1714

Example: 125 Gallons per minute x 1500 PSI /1714 = 109.4 Horsepower

The big dial on the dynamometer is simply a hydraulic pressure gauge that has several scales for various PTO RPM inputs. The scales on the dial have been calibrated from the various flow rates that result from the various PTO RPM?s. Keep in mind that for a specific constant RPM, the flow rate of the pump will be constant, regardless of what pressure it develops ? assuming the pump is in good condition. And for the HP reading to be accurate, the PTO RPM must be held to the appropriate speed based on the scale being read ? otherwise, the flow rate will not be what is should be and thus the dial reading of horsepower will not be correct.

Absorbing all that horsepower generates a LOT of heat. That?s why those dynamometers have water coolers in the oil reservoirs. For example, if the dynamometer reservoir contains 50 gallons of oil, and a tractor is developing 100 HP on the dyno, the oil temperature will rise about 24 degrees for each minute of operation. So sustained running requires cooling of the dyno oil by hooking up a garden hose to the dyno.
 

I have an A&W 375 dynameter that I had to rebuild a year ago. The simplest way to explain how my unit works is that there are 2 brake drums (similar to a big truck) that turns with the PTO. While the PTO is turning it also runs a small hydraulic pump which will supply hydraulic pressure to the system. As the operator turns the hydraulic valve by hand the internal brakes drags against the brake drum. The more pressure that you apply, the more HP will be required to maintain the PTO speed. This is similar to hitting the brake peddles, the harder you press them, the more force is being applied to the brakes.

There is a sensing bar that is attached to the internal brake (brake can only turn a few degrees), as you apply more pressure the brake wants to turn, but the bar restrict this as it is set on top of a hydraulic piston. The more the brake unit turns the more the hydraulic piston builds pressure. On my unit, the hydraulic pressure equates to the HP (it is scaled accordingly)


mvphoto48721.jpg




mvphoto48722.jpg





mvphoto48723.jpg





mvphoto48724.jpg
 
In case he's looking at another brand/model, what you very nicely describe is exactly what is under the hood of my Hydragauge 400 dyno.
 

We sell tractor parts! We have the parts you need to repair your tractor - the right parts. Our low prices and years of research make us your best choice when you need parts. Shop Online Today.

Back
Top