HYDRAULIC JACK or HYDRAULIC PRESS
The hydraulic jack is a device used for lifting heavy loads by the application of much smaller force. It is based on Pascal’s law, which states that intensity of pressure is transmitted equally in all directions through a mass of fluid at rest.
WORKING PRINCIPLE: The working principle of a hydraulic jack may be explained with the help of Fig. 23. Consider a ram and plunger, operating in two cylinders of different diameters, which are interconnected at the bottom, through a chamber, which is filled with some liquid.
Fig. Hydraulic jack Fig. Plunger
W= Weight to be lifted,
F = Force applied on the plunger,
A = Area of ram, and
a = Area of plunger.
Pressure intensity produced by the force F, p = F/Area of plunger = F/a
As per Pascal’s law, the above intensity p will be equally transmitted in all directions.
Therefore, The pressure intensity on ram = p = F/a = W/A or W= F(A/a)
Above Equation indicates that by applying a small force F on the plunger, a large force W may be developed by the ram.
Mechanical advantage of press = A/a
If the force in the plunger is applied by a lever which has a mechanical advantage (L/l) then total mechanical advantage of machine = (L/l)(A/a)
The ratio (L/l) is known as leverage of press.
Hydraulic jack may be employed for the following jobs:
- Metal press work (to press sheet metal to any required shape).
- Drawing and pushing rods.
- Bending and straightening any metal piece .
- Packing press.