18 May 2025

A COMPLETE GUIDE TO HYDRAULIC CYLINDERS IN LIFTING EQUIPMENT

To really understand just how essential hydraulic cylinders are in lifting equipment, you first need to briefly know: how does a hydraulic cylinder work? By converting the pressure created by hydraulic fluid being pushed through piping into mechanical force, it can lift impressively heavy loads with relative ease. This is an essential process in forklifts, cranes and car lifts, and gives the user the safer option of powerful, smooth movement with little to no manual handling.

As well as answering ‘how does a hydraulic cylinder work?’, this article is going to explain how to test a hydraulic cylinder,  how to repair a hydraulic cylinder, what their typical load capacity will be and much, much more.

WHAT IS A HYDRAULIC CYLINDER?

A hydraulic cylinder is a mechanical actuator that uses pressurised hydraulic fluid to produce smooth, powerful and linear motion and force. Essentially, it converts fluid power into mechanical power. This enables lifting, pushing, pulling or lowering heavy loads with precision and control.

Hydraulic cylinders are widely used in lifting and industrial equipment, including:

• Forklifts: to lift and tilt pallets safely

• Cranes: for raising and lowering loads

• Scissor lifts: to raise platforms vertically

• Diggers and excavators: for moving arms, buckets and attachments

• Industrial presses: for compressing or forming materials

• Tail lifts and vehicle lifts: to raise cargo or equipment efficiently

HOW DOES A HYDRAULIC CYLINDER WORK?

A hydraulic cylinder works by converting hydraulic pressure into linear force. Pressurised fluid, usually oil, is pumped into the cylinder, pushing the internal piston inside the barrel. This movement extends or retracts the rod in a fluid motion, generating the mechanical force needed to lift, push or pull loads of impressive weight.

Key components in what is a hydraulic cylinder:

• Barrel: The main body where the piston moves

• Piston: The part that separates fluid chambers and transfers force to the rod

• Rod: Connects the piston to the load being moved

• Seals: Prevents fluid leakage and maintains pressure

• Ports: Openings where hydraulic fluid enters or exits the cylinder

Hydraulic cylinders operate based on the basic principles of Pascal’s Law. This is a staple of engineering knowledge, which states that pressure applied to a confined fluid is transmitted equally in all directions. This principle allows a small amount of input force to create a much larger output force, essential for strong mechanical lifting.

HOW MUCH WEIGHT CAN A HYDRAULIC CYLINDER LIFT?

Pressure x area = force

Above is one of the basic equations that most workers in this industry will know. The ‘pressure’ part is the hydraulic fluid pressure being created, normally measured in psi (pounds per square inch), Pa (Pascal) or bar. The area is the bore size of the piston itself.

Example:
A cylinder with a 100 mm bore (0.1 m diameter) operating at 150 bar:

Piston area = π × (0.05)² ≈ 0.00785 m²

Force = Pressure × Area = 15,000,000 Pa × 0.00785 m² ≈ 117,750 N (newton) ≈ 12 tonnes

Like with most mechanical/engineering practices, this is all well and good until certain variables come into play. With hydraulic cylinder lifting, these variables can include the size of the piston. The bigger the piston, the more force is needed to move it. A higher amount of hydraulic pressure will provide a higher lifting capacity.

Then there are single- and double-action cylinders. Single-action can move heavy items in one direction, whereas double-action cylinders can lift and lower loads using hydraulic pressure in both directions.

HOW TO TEST A HYDRAULIC CYLINDER

Testing a hydraulic cylinder is an important part of workplace safety and management. To perform this pressure test, you can either attach pressure gauges to both ports or cap one port and apply pressure to the other to check for any leaks. The latter is known as a ‘bypass test’ and involves disconnecting one of the hydraulic cylinder’s hoses, capping that port and then performing the test.

The main signals to keep an eye out for that could mean there is something wrong with your cylinder are slow movement speeds, bumpy movement, a loss of force and contaminated fluid.

HOW TO REPAIR OR REPLACE A HYDRAULIC CYLINDER

Deciding whether to repair or replace a hydraulic cylinder starts with inspection. Repair is usually possible if leaks are limited to seals or wipers, the rod is straight with minor scratches and the cylinder bore and end caps are intact. Replacement will be needed if the rod is bent or heavily scored, the barrel is cracked or worn or there is structural or internal damage beyond repair.

Repairs typically involve replacing seals and wipers using a seal kit, honing the cylinder bore if needed or polishing the rod. Tools may include wrenches, snap ring pliers, a mallet, a torque wrench and sometimes a hydraulic press.

Safety is critical before removal. Depressurise the system, drain hydraulic fluid, support the equipment with blocks or locks and wear PPE such as gloves and safety glasses.

HOW TO CALCULATE HYDRAULIC PRESSURE IN A CYLINDER

Force ÷ area = pressure

Correct pressure matters greatly with hydraulic lifting. Consistently lifting over capacity will cause a strain on your lifting equipment, which will eventually lead to inefficient working and potentially dangerous breakdowns.

Example:
A cylinder must lift 10,000 N with a piston diameter of 100 mm (0.1 m):

1. Area = π × (0.05)² ≈ 0.00785 m²

2. Pressure = Force / Area = 10,000 N ÷ 0.00785 m² ≈ 1,274,000 Pa ≈ 12.7 bar

CHOOSING THE RIGHT SIZE HYDRAULIC CYLINDER

When asking, “What size hydraulic cylinder do I need?” or “How to determine hydraulic cylinder size?”, several factors must be considered. Stroke length determines how far the rod extends, while bore diameter affects the force the cylinder can generate. Mounting type impacts how the cylinder attaches and moves within your equipment. Load, speed and operating pressure are also critical to ensure safe and efficient performance.

CHOOSING THE RIGHT SIZE HYDRAULIC CYLINDER

When asking, “What size hydraulic cylinder do I need?” or “How to determine hydraulic cylinder size?”, several factors must be considered. Stroke length determines how far the rod extends, while bore diameter affects the force the cylinder can generate. Mounting type impacts how the cylinder attaches and moves within your equipment. Load, speed and operating pressure are also critical to ensure safe and efficient performance.

To select the right cylinder, match the bore and stroke to your force and travel requirements, choose a compatible mounting style and verify pressure ratings. For expert guidance, get in touch with LES® today.