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Help on power calcuations
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Virtual Machine Shop Forum  |  Machine Tool Technology  |  Questions, answers, ideas  |  Topic: Help on power calcuations « previous next »
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Geo.
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« on: September 23, 2016, 03:26:51 PM »

Hi All
I was writing lesson plans and I lost the formula for calculating brake horsepower by hydraulic pressure
This is what i have so far:


Definitions for Work and Power   
   Foot pound (ft-lb) = 1lb of force exerted over a distance of 1ft in any direction
   Power foot pounds per minute
   Horse power (hp) = 33,000 ft-lb per minute

Calculations for Work and Power   
   Horsepower for steam engines
o   hp = (P x L x A x N) / 33,000
   hp = Indicated horsepower
   P = effective pressure in in-lb per sq-in
   L = length of stroke in feet
   A = area of piston in sq-in
   N = number of strokes per minute ( = 2 x rpm for double acting engines)

   Horsepower for gas engines (simplified) (SAE)
o   hp = (D2 x N) / 2.5 = 0.4 X D2 x N
   D = diameter of Cylinders in inches
   N = number of cylinders 

   Brake Horsepower (bhp)
o   Determined by Pony brake (Old school: steel or leather belt carrying wooden blocks or shoes clamped around the flywheel with adjustment to vary friction on flywheel an lever arm is attached to the outside of band, the pull on lever by friction is measured by platform scale on which the lever rests)

   Actual power available for use 
   bhp = (2 x 3.1416 x L x N x W) / 33,000
o   L = length of lever
o   N = RPM
o   W = net force = scale reading weight of lever

o   Determined by Hydraulic pressure (Modern pony brake: engine runs a hydraulic pump, gage on output, valve on return line is slowly closed until engine loses rpm

Can anyone help out?
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Geo.
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« Reply #1 on: October 21, 2016, 07:59:36 AM »

Ok no takers?
and the answer is;

Basic Fluid Power Formulas
   Fluid Pressure (P) (PSI pounds per sq. in.)
   PSI = force / area (P= F / A)

   Fluid flow rate (Q) (GPM gallons per min.)
   GPM = Flow / Time (Q = V / T)

   Fluid power in Horsepower (HP)
   Horsepower = PSIG * Flow / 1714 (P * Q / 1714)
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