Hydraulic cylinders are a key component of hydraulic systems on modern heavy equipment such as excavators, skid steers and tractors.
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The cylinders use principles of fluid mechanics to translate hydrostatic pressure into linear force to power heavy equipment machinery and their attachments.
Typically, a hydraulic cylinder is filled with hydraulic fluid or oil. Inside the cylinder, a piston attached to a piston rod is moved back and forth inside the cylinder as fluid is pumped into and out of the cylinder at either side of the piston.
In turn, the moving piston causes the rod to extend and retract, powering the motion of arms, attachments and other mechanical systems on the machine.
Key to the performance of hydraulic cylinders are hydraulic seals, which are fitted around the piston, rod and other contact points inside the cylinder.
Hydraulic seals keep fluid from leaking out of the cylinder and ensure that excessive hydraulic fluid does not transverse the piston.
It is important to have the seals in your machine’s hydraulic system replaced by a trained professional. Seals that aren’t installed properly can lead to hydraulic fluid leaks, reduced power and rod drift.
Hydraulic cylinder seals are usually made of soft materials that are susceptible to damage. New seals need to be handled and installed carefully, and they must remain sterile.
Seals that become chipped, torn, dirty or cracked should not be used. Using seals that have become damaged during installation is a common cause for hydraulic fluid leaks.
Hydraulic leaks can be categorized as external or internal. External leaks occur when hydraulic fluid leaks out of the hydraulic system, whereas internal leaks occur when hydraulic fluid leaks between the different parts of the hydraulic system.
The most common cause of internal hydraulic leaks is a damaged or degraded piston seal. Piston seals are responsible for keeping hydraulic fluid from leaking across the piston.
Internal hydraulic leaks do not cause fluid to leak out of your machine, but they do cause a loss of power. Internal hydraulic leaks may also cause rod drift which affects your machine’s ability to hold hydraulic attachments in a static position.
External hydraulic leaks, on the other hand, are typically caused by a damaged or worn rod seal. When the rod seal becomes degraded from debris or heat, it loses its function and hydraulic fluid begins to leak out of the system.
When replacing the hydraulic cylinder seals on your heavy equipment, it’s important to choose the correct seal type. Utilizing a seal that does not fit properly or is not made of the right material will increase the probability of leaks and may allow contaminants to enter the hydraulic cylinder.
For best results, only use the size and type of hydraulic cylinder seal identified in your machine’s service manual. Here are some other factors to consider when choosing seals for your machine:
If you have the required tools and experience, installing new seals in a hydraulic cylinder is a straightforward task.
To attach the new seals, start by removing the old seals from the cylinder head and piston. If the seals are stuck, you can pry them loose with a flathead screwdriver or small file. Be careful not to score or scratch the cylinder’s components during this process.
Once the old seals have been removed, check the cylinder head and piston for any debris. If necessary, clean the piston and cylinder head with a damp rag. Be sure all moisture has evaporated from the parts before proceeding.
Next, begin inserting the new seals at the designated slots along the piston and in the cylinder head. Be careful that any seals with a lip, like the wiper seal, are oriented in the right direction. Installing seals in the wrong direction will allow dirt and debris to enter the cylinder.
Once the new seals are securely in place, look them over to make sure they haven’t sustained damage during installation. Any seals that have become chipped or torn cannot be used.
Reattach the piston and cylinder head to the cylinder to complete installation.
Seal kits are a convenient way to shop for new hydraulic cylinder seals for your machine. Seal kits are typically made for particular machines and cylinder types, so they take the guesswork out of choosing replacement seals for your heavy equipment.
The EquipmentShare Shop is a great source for high quality heavy equipment seal kits. Click below to find the right seal kit for your needs. For more help selecting hydraulic cylinder seals and seal kits, reach out to one of our parts experts and get personalized assistance.
Do you need help knowing which hydraulic cylinder will fit your machine? Could you use some guidance on choosing the right cylinder for your specific application? In this article, we will provide you with all the identifying information you will need and each step to take to measure before choosing which hydraulic cylinder to buy. Avoid returns, and get it right the first time!
Hydraulic cylinders are utilized in various applications and can be found on many machines, from scissor lifts to skid steers, tractors, and log splitters. As such, finding the cylinder you need can be a challenge. Whether this is your first time buying a replacement cylinder or you're DIYing a new log splitter, we're here to help you choose the right hydraulic cylinder for your project.
Before we discuss your options, let's quickly review the basic hydraulic cylinder components so that we can all understand the terminology in our buying guide.
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Watch our Parts of a Hydraulic Cylinder video for a visual guide to these hydraulic cylinder components.
Our video guide, How to Measure a Hydraulic Cylinder, demonstrates the step-by-step process of measuring a hydraulic cylinder.
Many factors must be considered when buying a new hydraulic cylinder, like the type of mounts required. The mounting type affects the cylinder's alignment, operation, and ability to handle loads. Common types include flange, clevis, or trunnion mounts.
The cylinder's speed and force requirements will dictate the size and type of the cylinder and the hydraulic system's power needs.
If you're replacing a worn-out cylinder, what are the specifications of the old one? Bore size, rod diameter, stroke length, and pressure rating are key to finding an exact match or an upgrade.
Do you need a single-acting or double-acting cylinder? The choice depends on the application and whether it needs to exert force in one direction (single-acting) or both directions (double-acting).
Identify the type of cylinder you need. RuggedMade offers the two most common types of cylinders used on various machines and across many applications: tie-rod and welded.
On RuggedMade's welded cylinders, the base is welded to the end of the barrel and is not meant to be removed. The cap at the gland end (where the cylinder rod moves in and out of the barrel) is threaded and can be removed.
On tie-rod cylinders, both the base and gland end can be removed. The gland and the base end cap are held together against the barrel using four threaded tie bolts or rods. These long bolts run the entire cylinder length and act like a vice holding the barrel caps together.
Several measurements describe a hydraulic cylinder. When replacing a hydraulic cylinder, accurately measuring the old one's dimensions will help ensure you buy the right one. One thing to keep in mind is that most manufacturers standardize measurements to the nearest whole or half inch. Four important measurements are used when sizing a cylinder.
We'll start with the hydraulic cylinder stroke length calculation because the question we hear most about sizing cylinders is, "What is the stroke length of a hydraulic cylinder?".
Stroke is the distance the rod and piston travel from the fully retracted to the fully extended positions. The simplest way to determine the stroke length is to measure the distance between the rod end pin center and base end pin center when the rod is fully extended and then when the rod is fully retracted. The difference between these two measurements is the cylinder stroke length.
For example, if the extended length is 18.25" and the retracted length is 14.25", then the cylinder has a 4" stroke (18.25 minus 14.25 equals 4).
If measuring from the pin center is too difficult, use the outer edge of each pin, but make sure you're looking at the same side for both (right to right or left to left, but not right to left).
If you plan on disassembling a cylinder, remember to measure the stroke first.
The next measurement is the cylinder port size.
As we said above, there are two commonly used types of ports: NPT (and NPTF) and ORB. The NPT type has tapered threads, while the ORB type has parallel threads. You can use a thread gauge and a thread gauge chart to help identify the thread standard. Measuring the size is tricky because the physical dimensions don't exactly match the nominal dimensions specified by the manufacturer.
If replacing a cylinder, you want the new cylinder to have the same size ports and, ideally, the same thread type. If you cannot find an exact match to the original port thread, you can use an adapter.
Another important measurement is the cylinder bore ID or the inner diameter of the barrel. The bore ID determines how much force the cylinder can generate. There are two ways to measure the bore ID.
The first method is to measure the outside width of the cylinder barrel and then subtract the width of the cylinder wall. For example, if the outside barrel width is 3.5" and the cylinder wall is 0.25", the bore ID is 3".
A more precise method involves disassembling the cylinder. This can be a messy process, but it allows you to use a caliper to measure the barrel's ID.
The final measurement is the cylinder rod OD. This is a straightforward measurement: Use a caliper to measure the outer diameter of the rod OD. Note that some cylinders have a tapered rod end.
When a clevis mount is threaded onto the end of the rod, the mounting dimensions may be changed, but the stroke doesn't change. It's the stroke measurement that matters most. When you can't find an exact match, a close match may work fine, but the stroke measurements must match.
Some mounts are designed to be greased, so make sure the new one is greased, too.
If you're curious about how changing the rod's size can change a log splitter's cycle time, check out our experiment in this video.
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