Hydraulic cylinders are similar to pneumatic cylinders, or air cylinders. The main difference between hydraulic and pneumatic cylinders is the fact that hydraulic cylinders use compressed fluid, while pneumatic cylinders use compressed air or gas.
Hydraulic cylinders have applications in industries such as agriculture, aviation, aerospace, automotive, robotics, waste removal military, machining, manufacturing, oil and gas, and construction.
In all of these industries, as they increase output force, efficiency and mechanical capabilities increase tenfold. Just a few of the machines they benefit are backhoes, cranes, brakes, dozers, forklifts, elevators, jacks, snowplows, dump trucks, ships, space crafts, planes, power steering, excavators, lifts, robotic arms, and material handling equipment. Toy manufacturers also use hydraulic cylinders to make water pistols.
Hydraulic cylinders are a product of the study of hydraulics. Modern hydraulics were born in 1648, the year that Blaise Pascal discovered what we now call “Pascal’s Principle” or “Pascal’s Law.” Pascal’s Law states that if and when you put pressure on one area of contained fluid, the pressure will spread evenly to the rest of the fluid.
While modern hydraulics were born in 1648, they did not take their first steps for nearly 100 years. In 1738, the Swiss mathematician Daniel Bernoulli put Pascal’s Principle, plus his own principle detailing fluid behaviors, called Bernoulli’s Principle, together to run successful mills and power pumps.
Then, in 1795, one of the most influential individuals of the Industrial Revolution, Joseph Bramah developed and patented his design for the hydraulically driven press; this was the first workable hydraulic machine. Bramah’s machine worked because it moved its press plate using liquid pressurized between two different sized cylinders. For his efforts, some call Bramah one of the fathers of hydraulics. One of the other people they call a father of hydraulics is William Armstrong. About 45 years after Bramah patented his hydraulic press, Armstrong developed, among other hydraulic equipment, a hydraulic crane. His efforts made it easier and more efficient for manufacturers to harness hydraulic power. Armstrong’s hydraulic crane also used a hydraulic cylinder, one he called a “jigger.”
Since the early days of hydraulic manufacturing, scientists and engineers have made many changes to hydraulic cylinder operations. For example, hydraulics rarely use water anymore, as engineers have since realized that water can encourage corrosion and rusting. To avoid corrosion, to harness higher power, and to stop rapid evaporation, engineers switched over to hydraulic oil fluid over 80 years ago.
Since the mid-20th century, hydraulic machines have become not only more common, but more powerful. For example, we have been able to use hydraulic cylinders to help power major machinery, like cranes. This has literally taken us to new heights, as construction workers have used hydraulic cranes to build everything from skyscrapers to large airplane components.
Hydraulic Cylinder Design
Customers and hydraulic cylinder manufacturers have quite a few options when it comes to material selection for various hydraulic cylinder elements.
Seals are available in a large number of different materials, such as nitrile rubber, polyurethane, fluorocarbon Viton, and other elastomers and even cast iron.
Scrapers/wipers are primarily made out of polyurethane, but they are also available in metallic materials for use in sub-zero temperatures.
Wear bands are usually made from a combination of bronze, PTFE, and reinforced woven polyester.
Pistons may be made from steel, stainless steel, brass, bronze, cast iron, or aluminum.
Cylinder bodies must be made from durable materials, such as stainless steel.
Considerations and Customization
When designing a hydraulic cylinder, manufacturers have to think about a few key design elements, including bore size, rod diameter, maximum operating pressure stroke, and materials. While manufacturers have a wide variety of standard hydraulic cylinders at their disposal, they can create for you a custom hydraulic cylinder. Find out your standard cylinder and custom cylinder options by talking over your application specifications with your potential suppliers.
All cylinders consist of a cylinder barrel, a base or cap, a head, a piston, a piston rod, seals, seal glands, and wear bands. They also all use hydraulic fluid.
The barrel is the cylinder body. Made mostly from a seamless tube, it exists to hold hydraulic pressure.
The base, also called the cap, exists both to enclose the pressure barrel at one end and perform mounting duties. It is secured to the barrel via threading, welding, tie rods, or bolts. Also, except in the case of a welded cap, an O-ring, or static seal, is placed in between the barrel and the cap.
The cylinder head encloses the barrel from the other end. Also featuring a static seal, it connects to the barrel through a tie rod, bolts, or threading.
The piston separates pressure zones inside the barrel, and cylinders use it to push, pull, steer, press, tilt, turn, or lift attached loads and heavy machine components. They are machined with grooves that allow metal or elastomeric seals and bearing elements to fit them perfectly.
The piston rod is attached to the piston by nuts, threads, or bolts. The piston transfers linear motion to it. Usually made of a hard chrome plated piece of cold rolled steel, the piston rod extends from the cylinder to the rod-end head. It also, either in the form of a mounting attachment or a machine thread, unites the hydraulic actuator and the machine component the hydraulic cylinder is serving.
The seals follow the piston rod. In this setting, seals are semi-soft, non-metallic rings that fit into cylinder grooves. There they form an assembly that blocks or separates fluid in reciprocating motion applications. There are different types of seals, including dynamic seals, rod seals, piston seals, double acting seals, and single acting seals.
The seal gland, in turn, is an area on the cylinder head upon which seals are affixed in order to stop pressurized oil from leaking past the space between the rod and the head. Usually, seal glands contain a primary seal, a secondary/buffer seal, bearing elements, a wiper/scraper, and a static seal. They use the scrapers/wipers to remove contaminants like dust, dirt, and moisture.
Wear bands serve as a buffer between metals.
One of the ways that hydraulic cylinders are divided is by the way they move.
Single acting cylinders (single-acting cylinders) move only in one direction along a vertical or horizontal plane or another prescribed angle.
Double acting cylinders allow the rod to move along planes in both directions. Double acting cylinders are more widely used than single acting cylinders.
Another way that hydraulic cylinders are grouped is according to their cylinder or barrel type. Two of most requested types of hydraulic cylinders in this group are tie rod hydraulic cylinders and welded hydraulic cylinders.
Tie rod hydraulic cylinders, or barrels, can handle the weight of heavy loads. This is because they have the reinforcement of external rods. Because of this strength, they often serve as heavy duty cylinders.
Welded hydraulic cylinders are much smaller than hydraulic tie rod cylinders, with lighter and smoother designs. However, they are just as high quality as tie rod cylinders. Because their parts are all welded together, they are more stable than cylinders with multiple parts. Customers purchase them most often to accommodate compact machines in industries such as agriculture and construction.
Also available are specialized cylinders, like telescopic cylinders and hydraulic rams, among others.
Telescopic cylinders are hydraulic cylinders that move in stages. This way, they can use longer strokes while still taking up a small amount of space.
Hydraulic rams function as large output pistons inside hydraulic cylinders used for cyclical water pumping. The hydraulic rams pass kinetic energy onto water when they force it to move. In turn, this kinetic energy helps the hydraulic pump function. Hydraulic rams are common in rural or remote locations where the installation of an electrical water pump is not possible.
Heavy duty hydraulic cylinders work in challenging and high flow environments, like industrial settings. They are designed to handle high pressures particularly well.
High pressure hydraulic cylinders generate high pressure. They are very small and lightweight, so customers can install them in a wide variety of spaces. Despite their small size, high pressure cylinders are very powerful. They work well in environments like material transforming and material testing, which require high pressure combined with medium or short strokes.
Mobile hydraulic cylinders are designed for work in mobile equipment, like personal lifts, snowplows, material handling vehicles, and construction machinery.
Stainless steel hydraulic cylinders are designed to work for applications that must remain hygienic and/or environments in which the cylinder will encounter highly corrosive influences.
Thread cap cylinders are hydraulic cylinders that feature an O-ring protected gland threaded head.
Small hydraulic cylinders are hydraulic cylinders that use strokes of an inch or smaller. Small hydraulic cylinders can accomplish highly precise moves.
Stepped cylinders are a type of double hydraulic cylinder, or two-way hydraulic cylinder. They offer a faster-than-average starting stroke that works up to a more powerful one.
Replacement cylinders are cylinders that manufacturers swap in for old cylinders that are broken or behind the latest technology.
To best equip them for the tasks they will perform, manufacturers can outfit hydraulic cylinders with all sorts of accessories. Examples include cylinder valves, hydraulic fluid, extra seals, and fittings like clevis fittings.
While it is true that hydraulic cylinders on their own can only power linear motion, they may do more if equipped with clevis fittings. Clevis fittings are U-shaped fasteners that can be attached to the end of a cylinder’s piston rod, thereby allowing it to move in an angular motion as well.
Because of the nature of their functions, hydraulic cylinders may eventually become damaged or corroded. To help maintain hydraulic system health, you can purchase replacement cylinders, also called re-engineered or redesigned cylinders, from time to time. These can serve not only to repair, but to bestow integrated upgrades.
How to Choose the Right Supplier
To help you purchase the highest quality hydraulic cylinders and accessories possible, we’ve listed some of those hydraulic cylinder manufacturers and contract manufacturers that we trust most. All of the companies listed on this page have proven their worth over and over again.
To figure out which one these manufacturers is right for you, before you do anything else, you need to write down your application specifications, including your budget, delivery deadline, and your preference regarding hydraulic cylinder repair services. This way, when you browse the companies we’ve listed, you can see which ones do and which ones do not provide the services you require. Narrow down our list to three or four top contenders, then reach out to each of them to talk about your project. Use your specifications list as a conversation guide. After you have spoken with each supplier, compare and contrast their quotes. Determine which one offers the best services, prices, and delivery options for you, and go with them.