Hydraulic Machine Mechanical Advantage

A simple hydraulic press

Let W = weight to be lifted,

F = force applied on the plunger,

A = area of the ram,

“a” = area of the plunger,

P = pressure intensity produced by force F.

We know that pressure P = Force / Area of plunger

P = F/a

As per the Pascal’s Law, this pressure P, due to the force acting on the plunger, is equally acting on all parts of the hydraulic system. So this same pressure acts on the ram too. So

P = F/a

But considering only the ram,

Pressure P = W/A.

So equating both the pressures, as they have to be equal,

W/A = F/a

So W = A/a * F.

But mechanical advantage can be defined as “the ratio of weight lifted to the force acting on the plunger.”

So M.A = W/F.

Lever for hydraulic press

A lever is used to gain a mechanical advantage when lifting heavy weights for which hydraulic systems already have reduced the force which has to be applied by multiples. By using a lever in combination with a hydraulic press, the mechanical advantage gained is further optimized.

Industrial hydraulic press

The picture at the left represents a typical industrial hydraulic press. It has a fixed cylinder in which a ram is sliding. To the lower end of the ram, a movable plate is attached. As the ram moves up and down, the movable plate attached to the ram also moves up and down between two fixed plates. When hydraulic fluid is supplied under high pressure into the cylinder, the ram moves down exerting a force, which is equal to the product of the intensity of the pressure of the hydraulic fluid and the area of the ram on which it acts. Thus any material placed between the movable plate and the lower fixed plate gets pressed or even crushed depending on the pressure of the oil supplied. The return weights, which are suspended along with the movable plate, ensure that the ram moves back up after the pressure inside the cylinder is released.

Thus we have seen the working of the hydraulic press and in my next article, we will discuss hydraulic accumulators.