The practical unit of power that is often used in mechanical engineering is horsepower (hp).
Horsepower is a unit of measuring energy.
A motor’s rotations per minute (rpm) at a given torque specifies our energy usage or horsepower requirement.
The actuator is the interface component that converts hydraulic horsepower back into mechanical horsepower. An actuator may either be a cylinder giving linear motion or a hydraulic motor giving rotating motion.
Mathematically, hydraulic horsepower is expressed as follows:
Hp = flow (gpm) x pressure (psi)/1714(constant)
A horsepower is the power of one horse, or a measure of the rate at which a single horse can work. When we specify an engine as 30 hp, it implies that the engine can do the work of 30 horses.
One horse is said to be capable of walking 50 m in 1 min, lifting a 90 kgf weight.
1 horsepower calculation: Power = Work done/time
=90 x 50 = 4500 kgf min.
1 hp = 4500/60 = 75 kgf m/s.
1 hp = 746 W
Energy is expressed in a larger unit called kilowatt-hour (kWh).
1 kWh = 1kW x 1h= 1000J/s x 60 x 60 s = 3.6x10⁶J
1 kWh = 3.6 x 10⁶J
1 Wh = 3.6 x 10³J
As all systems are less than 10% efficient and efficiency factor must be added to the calculated input horsepower.
Input hp=10 gpm x 1500 psi/1714(constant)) = 8.75 hp/0.85 (efficiency))=10 hp
Rule of thumb: 1 gpm @ 1500 psi = 1.0 input hp
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