Article updated: 21-10-2026
Summary:
A hydraulic system uses an incompressible liquid, usually oil, to transmit and multiply force according to Pascal's Law, which says that pressure is transmitted equally throughout the fluid: with an outlet piston 9 times larger than the inlet piston, 100 kg of force generates 900 kg of lift (in exchange for moving the small piston 9 cm for every 1 cm of the large one). In the elevator, the pump propels the oil to the cylinder to raise the cabin and, on the way down, the engine shuts off and the valves allow the oil to return to the tank by gravity in a controlled manner, without counterweight, without an upper engine room and with the load resting on the pit. With electronic fluid management, variable frequency converters (VVVF), biodegradable oils, automatic battery evacuation and the parachute valve, which blocks the piston if there is a pipe break, it is an efficient and safe technology. Your ally to lift smoothly and safely by taking advantage of the physics of pressure.
Hydraulic systems are present in a multitude of elements of our daily lives. In the brakes of a vehicle, heavy construction machinery, or the elevators of a residential building. Its operation is based on a surprisingly simple physical concept: taking advantage of the pressure produced in an incompressible fluid to transmit and increase force efficiently.
Next, we analyze in detail the operation of hydraulics from its physical foundations to its application in vertical transport.
What is a hydraulic system?
A hydraulic system is a set of interconnected components that uses a fluid (usually special oil or water) under pressure to generate, control and transmit mechanical energy.
Unlike gases, liquids have the property of being practically incompressible. This means that when a force is exerted on a fluid contained in a closed circuit, it does not reduce its volume appreciably. On the contrary, it transfers that energy entirely to all points of the circuit.
This feature allows small forces applied at one end of the circuit to be converted into large forces at the other end, allowing high loads to be lifted with very little mechanical effort.
The physical principle: Pascal's Law
The operation of all hydraulic technology rests on a principle formulated in the 17th century by the French mathematician and physicist Blaise Pascal.
How pressure is transmitted uniformly in a fluid
Pascal's Law states that Any pressure variation exerted on an incompressible fluid at rest within a closed container is transmitted with the same intensity, in all directions and over all walls of the container.
Mathematically, pressure (P) is defined as the force (F) divided by the surface or area (A):
Since the pressure remains constant throughout the fluid, if we connect two cylinders from different areas, the pressure exerted on the smaller one will be exactly the same as that experienced by the larger one.
Practical application: multiplying the force with a piston
Let's imagine two pistons interconnected by a conduit filled with oil:
- An input piston (small) with area A_1=3.14" cm"^2.
- An output piston (large) with area A_2=28.26" cm"^2.
Since the area of the second piston is 9 times higher than the firstThe force exerted on the larger piston will be 9 times greater than that applied to the smaller one. Thus, by applying a force of 100 kg on the small side, 900 kg of lift is generated on the wide side.
However, physics maintains the conservation of energy. To raise the piston large a distance of 1 cm, it will be necessary to move the small piston a distance of 9 cm.
An everyday example of this multiplication of force is a car's hydraulic brake systems, where pressure exerted by the foot on the pedal activates the wheel pistons to stop tons of moving mass.
How the hydraulic system moves an elevator car
In the field of lifting, Pascal's principle translates into a robust mechanism capable of moving an elevator car extremely smoothly.
Upwards: the pump generates pressure and pushes the piston
To raise the cabinThe system follows these steps:
- In the hydraulic power plant An electric motor connected to a pump is activated.
- The pump drives the oil contained in a tank towards the interior of the main cylinder.
- As the liquid accumulates in the airtight cylinder, the pressure increases progressively until the piston moves upward.
- The piston directly pushes the cabin structure (or it does so through a system of pulleys and cables in indirect shots), causing the elevator to rise smoothly.
Down: gravity and valves control the descent
During the downhill journey, the motor does not need to consume electrical energy:
- The gravity acts on the weight of the cabin itself, which tends to descend under its own weight.
- A valve group They open progressively to allow for the controlled return of the oil from the cylinder to the tank.
- The outlet flow rate is graduated millimeter to ensure a comfortable journey, progressive decelerations and precise braking at floor level.
Advantages of the hydraulic principle over other lifting systems
Compared to the conventional electromechanical traction Through cables, hydraulic technology provides significant structural and operational benefits:
- Energy efficiency on the decline: The engine remains completely off during downhill journeys, taking advantage of the force of gravity.
- Use of space: It does not require a machine room located at the top of the property or the opening, allowing the power plant to be located on lower floors or adjacent spaces.
- Lower structural load: The weight of the installation and the transported load falls on the moat and foundation of the building, not on the upper structure of the gap.
- Safety and easy evacuation: At the level of securityIn the event of a power outage, automatic evacuation systems can mechanically open the down valve (using auxiliary batteries) to bring the cabin to the lower floor and free the passengers.
From the basic concept to the modern hydraulic elevator: technological evolution
From the first devices based on large pressurized water plungers to current lifting standards, technology has evolved remarkably:
- Electronic fluid management: Modern systems incorporate advanced hydraulic plants that monitor the viscosity and temperature of the oil in real time.
- Frequency variation (VVVF): The integration of variable speed drives in the pumps allows the exact hydraulic flow to be adjusted according to the load, reducing energy consumption on the rise and maximizing comfort.
- Biodegradable fluids: Ecological and non-combustible oils are used that minimize environmental impact and increase operational safety.
If you want to expand your knowledge, read the article about them biodegradable fluids from our blog.
Frequently asked questions
Why doesn't the hydraulic elevator need a counterweight?
Unlike electric traction elevators, the hydraulic system supports the cabin using the incompressible fluid column and circuit pressure. By using gravity for descent, it dispenses with the counterweight, which simplifies physical installation and increases the usable surface area in the available gap.
What is the difference between a hydraulic system and a pneumatic one?
The key difference lies in the fluid used:
• Hydraulic systems: They use a liquid (oil). It is incompressible, ideal for moving large loads with precision.
• Pneumatic systems: They use a gas (compressed air). It is a compressible fluid, suitable for rapid movements and moderate forces.
Can the system fail if there is a pressure loss?
Hydraulic lifting circuits They are equipped with safety devices such as the parachute or flow interruption valve. If the oil return rate exceeds design limits due to a damaged pipe, the valve is mechanically locked in a fraction of a second, stopping the piston's movement.
Expand your knowledge by reading the article about the Parachute valve on our blog.
Bibliography
Halliday, D., Resnick, R., & Walker, J. (2014). Fundamentals of Physics (10th ed.). John Wiley & Sons.
Publisher's entry (current edition):
Fundamentals of Physics — Wiley
Also available on Amazon: Fundamentals of Physics — Amazon
Mott, RL (2006). Applied fluid mechanics (6th ed.). Pearson Education.
File in Casa del Libro:
Applied fluid mechanics — Casa del Libro
Cengel, YA, & Cimbala, JM (2018). Fluid Mechanics: Fundamentals and Applications (4th ed.). McGraw-Hill.
Publisher's entry:
Fluid Mechanics: Fundamentals and Applications — McGraw-Hill
GMV Fluid Power. Technical documentation on lifting regulations and fluid engineering. Official technical documentation from GMV Eurolift's own blog: gmveurolift.es GMV Quick Product Guide (technical catalog with specifications for hydraulic components): GMV Quick Guide (PDF) ITC AEM 1 “Elevators” (RD 355/2024): BOE-A-2024-7258
Is the current standard. The cables and relays are replaced by one or more electronic boards integrated with microprocessors, very similar to those of a current computer.
21 Responses
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Why are hydraulic systems able to multiply?
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