Sectieoverzicht

    • A machine that uses liquid to transmit a force is called a hydraulic system. The pressure in the liquid is the same everywhere in the system. The simplest type of hydraulic machine is made of two pistons connected by a liquid-filled pipe. If one piston is pushed, the force is transmitted through the liquid and the other piston moves. Hydraulic brakes on cars work like this.

      Liquids are used in hydraulic systems because they are more difficult to compress than gases, so are better at transmitting forces - when a force is applied at one end of the system, it is easy transferred through the system.

      car jack

      Pascal’s principle (also known as Pascal’s law) states that when a change in pressure is applied to an enclosed fluid, it is transmitted to all portions of the fluid and to the walls of its container. In an enclosed fluid, since atoms of the fluid are free to move about, they transmit pressure to all parts of the fluid and to the walls of the container.

      A simple hydraulic jack, like a car jack, is a good example of how Pascal's law is put into practice. Using such jacks, one can even lift buildings. 

      The hydraulic jack consists of a lever that pushes a piston into a narrow tube of some fluid, usually an oil. The lever allows a human to apply a lot of force to the fluid reservoir. The size of the fluid tube is expanded below a moveable piston that can be pushed upward to raise a mass. A reservoir of low-pressure oil and a couple of valves complete the jack so that it can be extended its full length, and sometimes further if the piston can telescope.

      Car jack 1

      When the lever is pushed downward, the one-way filling valve closes, and the lower valve (which allows flow only in the right → left direction (in this figure). Because the diameter of the pumping piston is smaller than the diameter of the lifting piston, the force is multiplied, and the rising jack can lift large masses.

      car jack 2

      To full the pump, the handle is raised. The high-pressure (lower) valve shuts off, maintaining the fluid pressure under the lifting piston. The filling valve opens, as it allows fluid movement from right to left (in the figure) only. Fluid from the low-pressure reservoir enters the pump and is ready to be pushed into the high-pressure side.

      car jack 3



      Fuseschool. (2020). Hydraulics. (Standard YouTube licence)

      A hydraulic press is a machine that uses Pascal’s Principle to generate a large amount of force. It consists of two cylinders, a smaller slave cylinder and a larger master cylinder. The slave cylinder contains a piston that is used to apply pressure to the fluid inside the slave cylinder. This pressure is then transferred to the master cylinder, where it is pushed by a piston.
      Hydraulic presses are commonly used for forging, clinching, moulding, blanking, punching, deep drawing, and metal forming operations. Hydraulic presses are also used for stretch forming, rubber pad forming, and powder compacting. The hydraulic press is advantageous in manufacturing, it gives the ability to create more intricate shapes and can be economical with materials. A hydraulic press takes up less space compared to a mechanical press of the same capability.
      a hydraulic press
      Hydraulic press maching


      Calculating the force on a piston:

      A hydraulic car jack is used to lift a vehicle. The area of piston A holding the car is 40 m2 and the area of piston B, which the mechanic presses, is 0.5 m2. The mechanic exerts a force of 100 N on her piston. What is the force exerted on the car by piston B? (Remember that the pressure is the same in the entire system.)

      First calculate the pressure on the surface of piston A:

      On piston A, a force of 100 N is exerted over an area of 0.5 m2.

      This is the pressure of the system.

      Pressure = Force normal to the surface/area of the surface

      Pressure = 100/0.5

      Pressure = 200 Pa

      Then calculate the force at piston B. First rearrange the equation to find force normal to surface area:

      Force normal to a surface area = pressure × area of that surface

      Force on piston B = 200 × 40

      Force on piston B = 8,000 N


      Activity

      What you will need:

      16 strong pieces of cardboard with a length 12cm and breadth of 1.5 cm, or 16 ice lolly sticks

      20cm long pipe 

      18 strong bamboo sticks. 

      Two syringes, 1 of 10mls and the other 20ml. You can also use same size syringe.

      Hot glue gun

      Sharp knife

      What you will do:

      1. Make 3 holes in each piece of card board. 

      pieces of cardboard

      2. Cut eighteen bamboos sticks into 10 cm lengths.

      3. Arrange all cardboard in crisscross and push through the bamboo sticks.

      5.  Seal the sticks into place with hot glue.

      6. Repeat this process for the other side.

      7.  Glue a cardboard platform to the top of the chain.

      8.  Glue one of the syringes, the pressing end to the chain. 

      9. Fill the second syringe with water, and using the pipe connect another syringe.  

      10.  Place an object onto the platform and using the syringe, lift the object up.



      DIY Projects. (2018). Hydraulic jack (Standard YouTube licence)

      Examples of hydraulic presses:

      1. Hydraulic Lifts - used for moving goods or people vertically. Scissor lifts, two-post lifts, four-post lifts, carousel lifts, and mezzanine lifts are different types of hydraulic lifts used.

      2. Hydraulic Brakes - Braking systems on vehicles are an important example of hydraulics. 

      3. Bicycle pump 

      4. Syringes

    • Hydraulic press Test
      Leerlingen moeten
      Een cijfer behalen
      Het slaagcijfer behalen