Logo
Innovative motion control solutions since 1947

Category: Hydraulic Cylinder

Hydraulic Cylinders: When Hysteresis Isn’t Funny

There’s a common phenomenon in literally 100% of hydraulic systems that simply must be taken into account, and it has the misfortune of bearing a name that makes it sound like something we should all be grinning at: hysteresis.

 

What Is Hysteresis?

Simply put, every single kind of hydraulic cylinder, hydraulic valve, or hydraulic end-device (winch, servo arm, whatever it may be) that has at least two directions of movement suffers from the same problem. That being, the pressure required to move them from one position and the pressure required to move them back aren’t the same pressure.

 

Let’s take the simplest example: a valve designed to open when pressure gets too high — a ‘release valve.’  As the pressure behind the release valve builds, it will remain steady until that pressure reaches a certain point — say, 500 psi — at which point the valve opens. As the pressure decreases, however, the valve does not then close at 500 psi; it will only close when the pressure hits a lower point — say, 480 psi. The difference between those two pressures is called the ‘hysteresis’ of the valve, and it’s most often given as a percentage — 480 being 96% of 500, we would say the hysteresis of the valve is 4%.

 

Hysteresis is also rate-dependent, so for example, bringing a given hydraulic cylinder slowly from one pressure to another will result in less hysteresis than if you just crank the control all the way over to the other side in one swift action.

 

Why is Hysteresis a Problem?

Hysteresis is a problem primarily because of the way in which the human mind thinks — we expect, for example, that if we put all of the settings on a given hydraulic circuit to the same positions they were in last time, we’ll get the same result. But because of hysteresis, the result you get as you increase the pressure to get to Point X can differ significantly from the result you get if you reach Point X by decreasing the pressure — and the results can vary even more if you increase and/or decrease the pressure quickly rather than gently.

 

The end result is that confident operators can do everything they are ‘supposed to’ in order to achieve a specific end result, and end up missing that end result by enough to cause a disaster on the job site. Minimizing hysteresis — and constantly monitoring it — are critical goals for every job site that relies on hydraulic circuits, especially when lives could be endangered by an error.

 

Importance of Hydraulic Cylinders

Have you ever paid attention to the importance of hydraulic cylinders in modern day construction? Every single tube you find on or under a machines arm while staring at a building in process is most likely one of these. As you may have guessed by the description given before, they are what power these arms in a unidirectional stroke in order to move or lift something which requires a lot of force.

The Power Itself

A hydraulic cylinder is made up of many parts like barrels and pistons, but mainly the force will come from a pressurized hydraulic fluid which tends to be oil. Inside the cylinder, this fluid’s flow is regulated by a pump which will in turn generate a pull force.

You will also find that there are two types of cylinders: Single acting and double acting.

  1. The first ones are simpler in design and generally cheaper. The oil enters through a port at one end of the cylinder, extending the rod which later gravity will send back into the piston.
  2. Double acting cylinders, on the other hand, have a port at each end and require the fluid to flow in or out of both sides for both movements (extension and retraction).

Different Designs

In the industry of hydraulic cylinders you will find many designs available:

  • Welded Body: it doesn’t have a tie rod and the barrel is welded directly into the end of the caps as well as the ports.
  • Tie Rod:  mostly seen in industrial factory applications, these hold the end caps using threaded steel rods.
  • Compact: utilized when the mounting space is expensive or difficult to acquire and the application demands a high force.
  • Telescopic: also called multi stage rod, due to the fact that it is actually a succession of rods tied together for force or distance required

Which One Should You Buy?

As you can see, there are many kinds of hydraulic cylinders in the market so the best thing to do is actually to ask for a professional’s help to suit your manufacturing or building needs. That way you’ll find the proper tool for the proper task.

 

Industry Uses for a Hydraulic Cylinder

There is a wide range of apparatuses of large automated systems and machinery that has been developed throughout the years in order to make things operate more efficiently and smoothly. Amongst the apparatuses, a hydraulic cylinder is also included. This component is a mechanical actuator, which produces unidirectional force via unidirectional stroke. A hydraulic cylinder has several applications, which are mainly based around construction equipment. Read on and discover the many instances where a hydraulic cylinder tends to be most valuable.

Agriculture

These devices are used a lot within agricultural industries, and can be used for a range of machines including loaders, harvesters, and tractors. In addition, they may also be used as attachments for hydraulic wood splitters, tractors, and more.

Civil Engineering

The civil engineering industry also calls for these devices for their machinery, as bulldozers, trenchers, excavators, and their attachments all feature hydraulic cylinders.

Energy Industry

These components also seem to come in useful for the energy industry. Hydroelectric stations that have gate controls make use of these cylinders, as these cylinders help with the possibility of opening and closing gates to control water flow.

Mechanical Engineering

Mechanical engineering also values these cylinders, as they come in extremely handy for automated production lines, forming machines, feeding devices, producing ecological equipment, transportation devices, and plastic forming machines.

Shipbuilding

Finally, shipbuilding is another industry that values the device. Hydraulic cylinders can be found in steering mechanisms, hoists, transportation equipment, and more.

Types

Many other industries that value the device include automotive, aeronautical, food, and construction. With the wide range of uses for hydraulic cylinders, having only one kind of this device can make things very difficult. This explains the several variations of the component. This ensures all the roles are undertaken correctly and the right type of the device is being used. The variety includes single-acting, double-acting, telescopic, and plunger cylinders.

Even though there are a couple of variations, they all feature the main components: the piston and barrel. Further components include the head, base, piston rod, deals, welded port, flange, rod end, bearings, bushes, and other small parts. A manufacturer of hydraulic cylinders puts these components together in order to make the device function properly.

 

 

Preventative Maintenance: Hydraulic Pumps

There’s no such thing as a part that doesn’t need maintenance, and that includes hydraulic pumps. Proper maintenance not only keeps parts working in the short term, but it reduces maintenance and replacement costs in the long term as well. The alternative leads to many minor problems in the short term that can become disastrous if left unattended. Preventative maintenance gives the best of all possible results.

For a hydraulic pump, preventative maintenance can be a fairly complex, multi-step process. Regardless of what else you’ll be doing to your pump, the first step is always to disconnect it from the power supply.

Basic Maintenance
Generally, the next step is to check the level of hydraulic fluid inside the pump. When all of the actuators are fully extended, the fluid level in the pump should be able halfway from the top. If it needs fluid, obviously, you should add more — if it seems to need fluid often, you should check the system for a leak.

Every so often (as dictated by your owner’s manual) you should drain the fluid from your hydraulic pump and give it a flush. Basically, you’re washing out the inside of the system, getting any particulate that might damage your hydraulic cylinders or other moving parts out. Then, refill with fresh hydraulic fluid.

Preventative Maintenance Example
Your owner’s manual should also explain how often you ought to clean the pump. While every system is different, a common example follows:

  • Remove the screws that attach the motor and pump assembly to the reservoir. Be careful not to damage the gasket or jolt the filter or pressure regulating valves while you extract the pump and motor.
  • Clean the inside of the reservoir, and refill with a suitable flushing fluid.
  • Place the pump and motor assembly back onto the reservoir, and attach with at least two screws on opposite sides of the mounting.
  • Run the pump for several minutes to clean it and flush out the system, then remove the motor and pump again.
  • Drain and clean the inside of the reservoir a second time.
  • Reassemble the entire unit completely, and fill with fresh, clean hydraulic fluid up to the fill line.

An AirStroke Actuator May Be Better Than Springs or Hydraulics For Your Needs

AirStroke actuators made by Firestone perform the same kinds of actuation tasks as the more commonly seen hydraulic and pneumatic cylinders, but for short-stroke, high-force tasks, have several advantages over their peers. AirStroke actuators are friction-free, leak-free, single-acting pneumatic actuators that have been used in a huge variety of industrial environments in the place of hydraulic or pneumatic cylinders.

You’re probably familiar with the traditional design of one of those cylinders: a tube of steel with a piston of steel inside, filled with either gas or hydraulic fluid. As more gas or fluid is added, the piston is pushed outward by the increase in pressure. Because the piston must be sealed tightly enough that the gas or fluid cannot escape, they require both constant lubrication and an environment free of particulate that might degrade the seal.

Firestone’s AirStroke actuators don’t have moving parts or seals, so they neatly sidestep both of those problems. They need no maintenance or upkeep, because they consist of naught but a strong, flexible outer wall that forms a tube capped on both ends by metal. When it’s empty, the outer wall collapses perfectly downward so that the metal caps are almost resting on top of one another. The metal endcaps have ports that allow air or fluid in and out; as the medium of choice rushes in, the endcaps are forced apart and the walls expand upwards, doing the job of a pneumatic actuator but with dramatically increased flexibility — they can operate with the top cap up 30 degrees off of vertical without a noticeable loss of power or efficiency.

With diameters between 2.2 inches and 37 inches, stroke lengths of up to 14 inches, and workloads of up to one hundred thousand pounds, AirStroke actuators can do almost any short-stroke, single-action job you’ve got. At less than 60% of the up-front cost of a similarly-purposed pneumatic or hydraulic cylinder and zero maintenance and upkeep, from an economic standpoint, the AirStroke is practically a no-brainer.

If you’re not certain whether or not an AirStroke actuator is the right tool for your job, contact Peerless Engineering today. We’ll be happy to offer you a free consultation on the powers and properties of these amazing industrial implements.

Hydraulic Cylinders: The Might Behind America’s Construction Crews

Hydraulic cylinders are used in large- and small-scale industry, from hand-held manual tools to massive construction vehicles and robots. A hydraulic cylinder provides the force that moves hydraulic fluid through its pipes, valves, and manifolds, where on the other end, it eventually reaches another cylinder that translates the movement of the hydraulic fluid into the movement of machinery. Hydraulic cylinders can be found in cars, cranes, oil rigs, bulldozers, draw bridges, and even in professional-grade long-reach pruning shears.

The primary components of a hydraulic cylinder are the cylinder, the piston head, and the piston rod. Mechanically, they work together much like a syringe — the piston rod pushes the piston head, which forms an airtight seal with the cylinder. The piston head forces the hydraulic fluid through the hole at the end of the cylinder. Because fluid cannot be compressed, and the entire sequence of pipes, valves, and manifolds is already full of fluid, any motion by the cylinder on one of the hydraulic series affects the cylinder on the opposite side without any delay.

Generally, the piston arm is powered by an electric motor, though there are plenty of exceptions. The outside of the cylinder and the piston arm are often painted with chrome for aesthetic purposes, but the inside of the cylinder and the piston head are under constant stress (as the hydraulic fluid pushes out equally on all surfaces of it’s container), so painting them would be counterproductive.

Cylinders come in several varieties. There are hundreds of different bores of cylinder available. They come in single-stage and double-stage (depending on whether you expect the force to some exclusively from one side or you need both sides to be able to move the other.) Cylinders are generally attached to reservoirs that contain additional hydraulic fluid and filters that keep the fluid free of impurities.

Quite often, a single powerful cylinder is used to power a variety of different motions within the same machine. In that case, a hydraulic manifold that can ‘switch’ one cylinder between several different endpoints is put into play. For any machine that only needs to make one motion at a time, a single hydraulic cylinder operating on a manifold makes for a lower cost of ownership over time.

A Layman’s Guide to Hydraulic Power Units

Hydraulic Power Units are machines that create mechanical force using fluids. HPUs (Hydraulic Power Units) are used in any industry in which large things need to be moved smoothly — construction, theme parks, farming, commercial fishing, and dozens more.

If you’ve seen a backhoe, loader, crane, power shovel, forklift, or garbage truck, you’ve seen an HPU in action. There’s an HPU in every set of the Jaws of Life as well. And of course, every mechanic uses a powerful hydraulic lifter to pick your car up and get to its underbelly.

One of the most commonplace hydraulic power units is in your car: the braking system of every car in the world uses an HPU. When you push the brake pedal in your car, you’re pushing hydraulic fluid (in this case commonly called ‘brake fluid’ for obvious reasons) into a hydraulic cylinder, which in turn pushes a piston, generating mechanical force that moves the brake pads up against the rotor, slowing your car. That’s why keeping your brake fluid levels topped off (and your brake lines free of air bubbles) is so important to your safety.

Hydraulics is a very powerful force because of a simple law of physics: while liquid can take on the shape of any container it’s put in, it cannot be compressed. What that means in short is that liquid can transfer force perfectly through almost any number of twists, turns, and corners without needing to involve a lot of gears, levers, and other mechanical parts prone to breakdown. Instead, the hydraulic fluid moves through hoses and tubes, using hydraulic valves to ensure it takes the path you need it to take in order to perform the task at hand.

Hydraulic fluid is almost always some combination of petroleum oil, water, and antifreeze — dependent on the specific job the machine is intended to perform. A hydraulic filter keeps the fluid free of contaminants, and when unused, the fluid sits in a special container made to remove air bubbles from the fluid. Thus, the fluid remains in working order for as long as possible, and your HPU can continue functioning continuously for years with minimal maintenance.

These powerful machines are among the most versatile (and surprisingly common) of our mechanical aids. Everyone ought to know at least a little bit about the hydraulic power units that help them throughout their lives.