Horsepower, defined

In the cgs system, power has the units of ergs per second in the mks system, units of joules per second lor watts) and in the English system, units of foot-pounds per second. A common engineering unit is the horsepower, defined as 550 foot-pounds per second or 33.000 footpounds per minute. The SI unit of power is the wall. I watt = I joule per second. < I joule is the work done by I newton acting through a distance of I meler.l I joule = watt-second = I07 ergs= I07 dyne-centimeters. The SI unil of force is the newton. (I newton = 10s dynes). See also entry on Units and Standards. 

The speed and horsepower define the torque required for the system. The torque in turn. sets the shaft size and gear box size. 

The scope and terms used are well defined and includes a listing of standards and codes for reference. The purchaser is required to make decisions regarding gear-rated horsepower and rated input and output speeds. 

The operating envelope defines the physical requirements, dimensions, and type of coupling needed in a specific application. The envelope information should include shaft sizes, orientation of shafts, required horsepower, full-range of operating torque, speed ramp rates, and any other data that would directly or indirectly affect the coupling. 

These values, in conjunction with N and the horsepower requirements, completely define the major parameters of the systems. 

The required service factor is an important specification. The service factor is defined as the ratio of calculated basic horsepower to the applied horsepower. The service factor can be as high as 2 for spiral-bevel reducers, but with continuous service this factor could be as low as 1.25 to have a good reducer life. 

In order to select the most economical drive for an Injection molding machine, the duty cycle must be calculated (3). This calculation must be made for each specific application to determine the applicable motor rating. A typical duty cycle Is shown In Figure 3. The motor rating Is defined In terms of 1) Nameplate horsepower and service factor (SF) and 2) Breakdown torque In terms of full load. One first calculates the RMS HP via Equation (1). ... 

Power is the rate at which energy is transferred, and therefore it has dimensions of [ML2/P]. One watt (W) is defined as 1 J/sec. Other common units are horsepower and Btu/hr. (Curiously, the metric cheval-vapeur is equivalent to only 735 W, slightly less than the U.S./British horsepower of 746 W.) See Table A-9 for interconversion factors for these units. 

The unit for work and mechanical energy in the fps system is the foot-pound force (ft-lby ). Power is measured by an empirical unit, the horsepower (hp), defined by... 

For a motor-driven compressor, the maximum amperage rating on the motor defines when the compressor is work- or horsepower-limited. Check the amp load in the motor "breaker or "switch" room. 

We next define the mechanical measure for dynamic performance as hp/ton (engine horsepower available)/(ton of total weight). Clearly the large this parameter, the more muscle there is available to quickly accelerate the vehicle. 

For systems in operation, the four "fan laws" are particularly useful to the industrial hygienist and engineer in predicting the effects of changes in operating parameters. These laws define the relationships between the following parameters volume flow rate (CFM), revolutions per minute (RPM), horsepower (HP) and static pressure (SP). The four "laws" arc as follows ... 

NOTE The horsepower (mechanical) is defined as a power equal to 550 foot-pounds-force per second. ... 

The hydraulic horsepower, HHP, imparted to a fluid is defined as the product of the pressure (not head) developed and the flow delivered ... 

For the fractional-horsepower motor used in the laboratory or pilot plant, power draw is best determined by calculation using the defining equation for the power number. This requires power number versus Reynolds number data or correlation. 

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