Telescopic hydraulic cylinders, sometimes called multi-stage cylinders, are a type of linear actuator consisting of a series of tubular rods called sleeves. The sleeves (usually 2 to 6) sequentially decrease in diameter and are nested inside of each other.

Once hydraulic pressure is introduced to the cylinder, the largest sleeve is extended first. Once the largest sleeve has reached its maximum stroke, the next sleeve begins to extend. This process continues until the cylinder reaches its last stage, called the plunger.

There are three common types of telescopic cylinders: Single-acting, Double-acting, and a combination of single and double-acting.

Double Acting

A cylinder in which fluid force can be applied in either direction to the moveable element. These cylinders are also classified as differential cylinders because of their unequal exposed areas during extend and retract. The difference in effective area is caused by the area of the rod that reduces the piston area during retraction. Extension is slower than retraction because more fluid is required to fill the piston side of the cylinder. However, more force can be generated on extension because of greater effective area. On retraction, the same amount of pump flow will retract the cylinder faster because of the reduced fluid volume displaced by the rod. Less force, however, can be generated due to less effective area.

Single Acting

A cylinder in which hydraulic energy can produce thrust or motion in only one direction. Once the pressure is released, the load (can be spring or gravity returned) on the cylinder retracts the rod. The inactive end is sometimes vented to atmosphere through a breather/filter or vented to reservoir below the oil level.

A hydraulic cylinder is made up of 7 main components:

1. Cylinder Barrel (Main, Body). The barrel is the cylindrical body of the cylinder. The barrel guides the piston and provides a sealing surface for the piston seal. The barrel is also the structural part of the cylinder that holds the ends in place.
2. Cylinder Cap (Back End, Blind End, Blind Head, Rear End). A cylinder end closure which completely covers the bore area (opposite the rod end).
3. Cylinder Head (Packing Gland, Stuffing Box, Head End, Front End, Front Face, Rod End). The head gland or stuffing box is a cylinder component that serves more than one purpose. It retains the static and dynamic seals at the head end of the cylinder, it seals off at the end of the cylinders, it is the support or guide for the rod and it is the mechanical stop to keep the piston from falling out of the cylinder barrel.
4. Piston. The piston is a cylinder component that has multiple purposes. The piston retains the primary seal from the extend side of the cylinder and the retract side of the cylinder. It is the component that moves back and forth from the hydraulic oil. The piston is the mechanical means of connecting and moving the rod in and out of the cylinder as well as serves as a guide for one end of the piston rod.
5. Piston Rod. The rod is also known as the cylinder shaft, plunger or ram. It is the round device that moves in and out of the cylinder. The piston rod can be solid or hollow. The rod is usually plated, or heat treated to provide better wear and corrosion resistance.
6. Ports. Cylinder ports are the means in which the cylinder is able to have fluid lines or conduits connected. O-ring Boss (SAE) Port is a port that has straight or parallel threads as well as an O-ring to seal the threads. Pipe port threads are tapered threads that count on interference between the male and female threads to do the sealing. 4-Bolt Flange Port is a port that counts on 4 bolts to hold to two halves together. This type uses an O-ring to do the sealing. BSP is a British Standard Pipe Thread.
7. Seals.
   1. Static seals keep the joint pressure tight.
   2. Rod wiper / scraper is provided to remove and prevent foreign material from entering the bearing and seal area.
   3. Rod seals hold pressure in the cylinder by preventing fluid from leaking out.
   4. Piston seals prevent pressurized fluid from leaking across the piston as the system pressure pushes the piston and rod assembly down the cylinder bore.

The three most common hydraulic cylinder configurations are piston hydraulic cylinders, telescopic hydraulic cylinders and plunger hydraulic cylinders. Each cylinder design varies by the type of application as below: 

• Piston hydraulic cylinders are the most common on the market and can be designed with welding (welded hydraulic cylinders) or without (tie-rod hydraulic cylinders). Also, any piston cylinder can be suitable for single and double acting applications. 
• Telescopic hydraulic cylinders consist of a minimum of two stages or more and able to provide an extremely long cylinder stroke (travel distance) from a compact collapsed length of the cylinder body. Just like piston cylinders, telescopic cylinders can be single and double acting.
• Plunger hydraulic cylinders do not have piston. Therefore, plunger cylinders require a larger size of the hydraulic rod in order to create the same amount of force compared to piston cylinders. Also, plunger cylinders are suited only for single acting applications.

For all types of cylinders, the crucial measurements include cylinder stroke, bore diameter and rod diameter. Stroke lengths vary from less than an inch to several feet or more. Bore diameters can range anywhere from an inch up to more than 24 inches, and rod diameters range from 0.5 inch to more than 20 inches. In practice, however, the choice of stroke, bore and rod dimensions may be limited by environmental, application or design conditions. 

For example, space may be too limited for the needed cylinder stroke length. For tie-rod cylinders, increasing the size of the bore also means increasing the number of tie rods needed to retain stability. Increasing the diameter of the bore or piston rod is an ideal way to compensate for higher loads, but space considerations may not allow this, in which case multiple cylinders may be required.

Many of the failures in a hydraulic system show similar symptoms: a gradual or sudden loss of high pressure, resulting in the loss of power or speed in the cylinders. In fact, the cylinder may stall under a light load or may not move at all. Often the loss of power is accompanied by an increase in pump noise, especially as the system tries to build up pressure. Any major component, including the pump, the relief valve, directional control valve, or the cylinder, could be at fault. In a sophisticated system, other components could be to blame, but this could require the service of an experienced technician. By following an organized step-by-step testing procedure in an orderly fashion, the problem can be traced to a general area, and then if necessary, each component in that area can be tested or replaced. We want to discuss the safety tips concerning cylinder design and use. What are some of the suggested things we should be looking for when selecting the right hydraulic cylinder for the job? Answering these questions before installation is a great start to safe and optimal cylinder design.

– Is the hydraulic cylinder rated for the work to be done? Using the F = P x A formula (Force = Pressure x Area of the piston) will ensure that the cylinder is sized properly to do the work at the required system pressure. 

– Is the cylinder designed to handle the load? With so many hydraulic cylinder manufacturers today, choosing a replacement cylinder that will hold up to the load requirements is important. Be sure to evaluate the cylinder seals and guide bands compatibility being used. Agricultural equipment typically uses ag-type hydraulic cylinders that feature cast end covers bolted together with bolts and nuts onto a honed tube (tie-rod cylinder). They also typically use O-rings for seals. These cylinders generally operate at 1,500 – 2,500 PSI and are designed to be either quickly resealed in the field or thrown away. Using tie rod cylinder in a construction application would prove to be dangerous and self-defeating as it would have a short life span for the work to be done and may not hold up under the load requirements. 

– Tie-rod or welded? When is it appropriate to use a tie rod cylinder or a welded cylinder? The typical response is that manufacturers of stationary equipment generally rely on tie-rod cylinders, as they can be configured to fit most unique applications and have many applicable valving blocks, making them simpler to configure for machinery. This reduces other possible needed valves to accomplish work desired and helps to reduce costs. Rated to NFPA standards, tie-rod cylinders are easily inter-changeable with other manufacturers. Welded hydraulic cylinders are the most common in mobile equipment where weight and size of application work needs can be considered. These heavy-duty designs are usually rated at 2,500 – 5,000 PSI or even higher. Featuring a barrel that is bolted or welded directly onto the end caps, these designs do not require tie-rods, so these cylinders are much stronger and more resilient in harsh environment.

It is important to be sure to use a hydraulic cylinder that is rated for the needed job. Choosing a cylinder because of the cost rather than design can be a mistake in many ways. Pressure seals, wear bands, rod seals, and porting all play an important part of the selection.

Side loading

Side loading is a very common hydraulic cylinder failure, which is caused from the cylinder being misaligned which creates an unparalleled force on the piston rod. Hydraulic cylinder is a linear motion product that supposed to operate strictly back and forth as well as cylinder is not supposed to play a role of support or frame. Thus a side load of enough magnitude can result in cylinder tube scoring, hydraulic cylinder rod failure, rod guide bands, and most definitely hydraulic seals failure.

Contaminated Fluid

Contaminated fluid can cause premature rod seal failure. Abrasive particles in the fluid can damage the seals and the piston rod surface, airborne contamination can be drawn into a cylinder by a faulty rod wiper seal. Contamination occurs in numerous ways, the most common is drawn with hydraulic oil from the hydraulic pump that pushes oil of the oil reservoir. Since hydraulic oil travels in circuit among all hydraulic components, the damage from contamination can occur on any of the following parts: hydraulic cylinder, hydraulic gear pump, hydraulic control valve, check valves, etc. It is always recommended to have hydraulic oil filters in place for the most of hydraulic application.  

Rough or scored rod

Rough surface on the hydraulic cylinder rod damages rod seals and reduces their life expectancy, resulting in the necessity for frequent replacement. Rod surface smoothness strictly depends on the quality of rod manufacturer. The proper procedure to manufacture hydraulic steel rod should look like this: rod grinding according to the desired tolerances, polishing to achieve smoothness, then applying chrome plating bath and the final stage would be the finishing polish. Unfortunately a lot of cylinder manufacturers nowadays do not polish rods prior to chrome plating due to the market demand for cheaper alternatives, even though it is vital. Industry standard tolerance for cylinder rod smoothness is f7 which is designed for accurate machines operated at moderate speeds and journal pressures.

With rough cylinder rod, equipment would be able to operate regardless, despite shorter life span of cylinder seals and need for more frequent maintenance. Scored or scratched cylinder rod on the other hand, cause rod seals damage immediately. Damaged rod pressure seal allows oil to pass through the gland and create external cylinder leakage. That’s why cylinder rod has to be installed and operated with care, to prevent mechanical damage. The other way to get around this problem is to use induction hardened (IH) rod instead. IH rod is resistible to scores and scratches, however it comes at a higher cost.

Aggressive Environment

Hydraulic cylinder are often installed on the equipment operating in aggressive environment, such as salt water, salt air and acid conditions. The most common hydraulic cylinder failure under these conditions, is corrosion of steel components. Therefore corrosion can cause fluid contamination, permanent seals damage, and cylinder tightness. Suggested plating for the cylinder rod in the above listed environments would require nickel plating instead of chrome. Nickel plated hydraulic rods can withstand up to 1,000 hours in salt spray tests. The most superior option for the extreme conditions and expensive projects, is stainless steel nickel plated rod. It is definitely the best global solution however it bares proportional cost to it.

Hydraulic cylinders take a significant part of the entire hydraulic system. They are mechanical actuators that provide the unidirectional force. Integration of hydraulic cylinders will eliminate the presence of levers and gears. Both mobile (front end loaders, hydraulic lifts, construction vehicles, tractors, auto cranes,) and industrial systems (hydraulic presses, agricultural machines, marine equipment, forges, and packing machines) utilize hydraulic systems. Among them, most of the applications use hydraulic cylinders for lifting, sliding, picking and gripping.

Before performing the repairs, clean the surface properly and disconnect the hoses and plugs attached to it. Make sure that you work area is clean and neat. After disconnecting the parts, drain all the fluid present inside the cylinders and hoses. For repair of the hydraulic cylinder, we need some tools. Proper hydraulic cylinder seal kit, rubber mallet, screwdriver, punch, pliers, emery cloth, and torque wrench are the tools required for repairing. Leaking hydraulic cylinder is the most common issue that results in a cylinder repair. Disassembly of the cylinder, diagnosing the cause of failure, repairing or replacing faulty components, and rebuilding the cylinder are the steps involved in cylinder repair. During the process of hydraulic cylinder repair, always consider the below-mentioned cylinder repair tips.

• If you disassemble the hydraulic cylinder as a part of repair, inspect not only the failed part but also perform a thorough inspection of all other hydraulic cylinder components.
• Hydraulic wear bands (also called wear ring or guide ring) are used for guiding pistons. So, don’t forget to assemble the wear band because this will eliminate the metal-to-metal contact.
• Premature failure of rod seals indicates the bend or scratch on the hydraulic rod.
• Metal tools will scratch the surface of the cylinder rod or cylinder barrel and will create problems like corrosion. So always choose the best-fit tools for repairs.
• Larger hydraulic cylinders use high tension springs. Therefore, if you are an inexperienced hydraulic technician, be careful while handling such cylinders.
• For hydraulic cylinder seals replacement, don’t measure the existing size of the seal. It will expand or compress according to the environmental condition. The best option to replace seals is to contact your hydraulic equipment manufacturer and order a proper seal kit for the particular cylinder you need.

As a part of the scheduled hydraulic cylinder maintenance process, always check the chrome plated rod, cylinder seals, hydraulic cylinder tubing, cylinder gland and piston. During the inspection, if you found the hydraulic rod being damaged, remember that your system is under danger. The rough rod surface will increase friction. Therefore, the rod must be polished to lower the friction. These maintenance procedures will reduce failures to a greater extent.

Bore Diameter = Inside Tube Circumference / 3.1415

Rod Diameter = Rod Circumference / 3.1415

Stroke = Extended Length (center to center of pins) – Retracted Length (center to center of pins)

Volume Displacement in gallons = (Bore Radius² * 3.1415) * Stroke / 231

Fluid Pressure (PSI) = Force (lbs) / (Bore Radius² * 3.1415)

Force (lbs) = (Bore Radius² * 3.1415) * Pressure (PSI)

Fluid Flow Rate (GPM) = Volume displacement (gallons) / Time units (minutes)

Column Load (lbs) = pressure (PSI) * (Bore Radius² * 3.1415)

Hydraulic Horsepower = pressure (PSI) * Fluid Flow Rate (GPM) / 1714

Cylinder Extending Speed(Inch per second) = (231 * GPM) / (60 * Bore Radius² * 3.1415)

In most times, a hydraulic cylinder can be repaired by changing out pistons or seals inside the cylinder. However, on rare occasions, you may need to replace the entire cylinder itself. If that situation arises, you will need to know how to correctly remove the old hydraulic cylinder and install a new one. This easy-to-follow how-to guide will show you to do just that.

Step 1 – Prepare to Work

First, disconnect the negative battery cable from the terminal post on your battery.

Step 2 – Jack Up the Vehicle (if needed)

Jack up your vehicle and place it on jack stands, so that you can work with the hydraulic cylinders on your vehicle.

Step 3 – Remove the Hydraulic Hose

Depending on your equipment, the hoses may be held to the cylinder using clips or clamps. However, in most cases, you’ll be able to remove the clamps with a wrench or other tool. Remove the screw from the clamp that holds the clipper clamped in place and disconnect the hose.

Step 4 – Remove the Hydraulic Cylinder

Remove the pins/bolts that hold the hydraulic cylinder in place.

Step 5 – Drain Hydraulic Fluid

Place a plastic bucket or container underneath the cylinder and hoses to catch the hydraulic fluid that may drain out. Then, hold the cylinder upside down in order to drain the remaining fluid into the bucket or plastic container.

Step 6 – Clean the Cylinder Area

Take a rag or towel and wipe the area where the hydraulic cylinder was installed to remove any dirt or grime in the area.

Step 7 – Install New Hydraulic Cylinder

Use the pins/bolts that were used to hold the hydraulic cylinder in place when installing the new hydraulic cylinder. Be sure to apply a sufficient amount of torque to the bolts to ensure that they won’t be loose when the vehicle is being operated.

Step 8 – Re-connect Hydraulic Hose

Connect the hydraulic hoses to the cylinder. Then, push the clamp or clip up to the end of the hose so that it can hold the hose in place. Tighten the bolts that lock the clamp or clip.

Step 9 – Fill with Hydraulic Oil

Locate the port on the master hydraulic cylinder and remove it or the cover. Fill the master cylinder with hydraulic oil and connect the hose. Then extend the cylinder using hydraulic system and fill the other side of the cylinder with hydraulic oil (for double-acting hydraulic applications).

Step 10 – Lower the Equipment

Remove the jack stands (if any) and lower the machinery.

Why do hydraulic cylinders start leaking?

Seals play a major role in hydraulic cylinders – they contain the fluid and prevent the leakage of fluid. The seals for a rod sealing system protect the reciprocating motion for the piston rod and gland.

Here are some types of seals you will normally find in a Hydraulic Cylinder:

• Piston seals — keeps oil on the work side of the piston. Prevents oil travel between cylinder sides.
• Rod seals — prevents any leakage from inside the cylinder to the outside.
• Buffer seals — absorb changes in pressure when working with high-load conditions. Normally found in front of the rod seal.
• Wiper seals — prevent any outside contaminants or debris from entering the cylinder system.
• Wear bands — guide the piston and rod. Also prevents metal to metal contact.

Listed below are some common reasons for seal failures:

• Hardening — too much heat being generated from a high-speed application or environmental conditions surrounding the cylinder.
• Wear — excessive wear due to lack of lubrication.
• Contamination — any small pieces of metals or debris entering inside can damage inside components.
• Fracture — resulting from excessive back pressure
• Improper Installation — not using the proper tools to install seals can lead to damage and leaks. Most manufacturers offer installation tips, including surface specs and groove dimensions.

In order to measure and decide which hydraulic cylinder you need, first of all you would have to visually determine the type of hydraulic cylinder you try to replace. Here are the the main three types of hydraulic cylinders:

1. 1. Piston rod cylinder – has piston inside, can be single and double acting (ex. Clevis cylinder)
   2. Plunger cylinder – mostly is a single acting cylinder (ex. Snow plow cylinder)
   3. Telescopic cylinder – has multiple stages, can be single and double acting

Main hydraulic cylinder attributes are as follows:

• • Bore diameter
  • Rod diameter
  • Retracted length
  • Extended length
  • Stroke
  • Mounting ends
  • Hose ports
  • Working pressure

Here is a detailed guide on how to properly take measurements of any plunger or piston rod hydraulic cylinder. For this procedure you need such tools as a simple tape measure and a caliper.

• STEP 1:

Piston diameter or inside barrel diameter is the main dimension of the hydraulic cylinder and known in the hydraulic industry as “BORE”. Therefore it has to be measured first. If your cylinder is taken apart, simply measure either inside diameter of the barrel (cylinder tubing) or measure actual piston diameter across.

However if the cylinder is assembled and/or installed on machinery, BORE can be defined by measuring the outside diameter of the cylinder barrel (tubing) and subtracting thickness of both tubing walls. For example, outside barrel diameter is 1.88”, less 0.19” for each wall, so the BORE = 1.88” – 0.19” – 0.19” = 1.5” BORE. To make it easier for our customers, we listed the most possible options for industry standard tubing sizes below. You can compare your numbers to this table and easily analyze what BORE diameter you have on your cylinder.

• STEP 2:

The next step is to determine rod diameter. Rod of the hydraulic cylinder is a round chrome plated steel bar that performs reciprocating motion. As commonly described by our clients, it’s a shiny part that comes out from the cylinder. Caliper can easily take care of rod measurement. Simply measure rod diameter (thickness) with a caliper. Rod is one of the most significant parts in the hydraulic cylinder because main force during operation applies on the rod. Proper analysis of rod size and specifications will prevent bend rod situation.

• STEP 3:

Next thing to do is to measure the retracted length of the cylinder. Retracted length is the distance between centers of cylinder mounting pins (pin holes) when the hydraulic cylinder is completely retracted inside (closed). Retracted length can be measured with any standard tape measure. Without this measurement, the cylinder will not be installed and operated properly on machinery.

• STEP 4:

Extended length should be defined next. Extended length is exactly the same as retracted length described in step 3, with the only difference that hydraulic cylinder has to be fully extended (open) when measured. Just like with retracted length, use tape measure. It is a fairly simple procedure unless your piece of equipment is down and the hydraulic cylinder is not functional. In a situation like this, you would have to take the cylinder off the machinery and extend it manually.

• STEP 5:

With both above lengths on hand, we can calculate the stroke of the hydraulic cylinder. Stroke is a travel distance and calculated simply by subtracting one from another. Stroke = extended length – retracted length. Yes,it’s that simple.

• STEP 6:

After we noted all primary dimensions of the cylinder, it’s time for secondary ones. There are thousands of possible options on how to mount the hydraulic cylinder on machinery. Every original equipment manufacturer creates their own design. However the most popular type of mounting is the one with pivot pins. These pins connect hydraulic cylinder on each end with an equipment frame. Therefore to make sure that hydraulic cylinder replacement can be installed on your machinery, pivot pin diameter has to be measured using a caliper.

Huge selection of various machinery units created hundreds of different cylinder mounting end styles. However they can be separated on a few most popular segments:

• • Cross tube hydraulic cylinder – cylinder with two tubes welded across on both sides
  • Clevis end hydraulic cylinder – cylinder with U-shape coupler and through holes inside
  • Tang hydraulic cylinder – cylinder with solid welded steel ends of different shapes
  • Swivel eye hydraulic cylinder – cylinder with spherical bearings installed on each end
  • Trunnion hydraulic cylinder – cylinder with two symmetrical rods welded to a barrel

Based on the selection above, you should choose which option is the one you have. You have to make sure that outer dimensions are within your frame allowances for a proper fit.

• STEP 7:

Evaluation of existing hydraulic hose ports. Hydraulic cylinder port is the place where you connect hydraulic lines with oil. Hydraulic hoses basically power up the hydraulic cylinder. Each hose has two ends with crimps which can be either male or female. The most popular design is where the cylinder has female ports and requires male hose crimps to be connected. Every hydraulic port has two more designations: thread type and size. The most common thread sizes are ¼”, ⅜”, ½” and ¾”. Where the most popular hydraulic threads in the United States are SAE (O-ring Boss), NPT (National Pipe Thread), JIC (Joint Industry Council), and Flat Face. We have a separate, more detailed guide on threads which you can find in our FAQ section. If you analyzed that your thread is different from the cylinder you chose in our catalog, no worries, it’s an easy fix. There are thousands of different adapters available online at affordable prices.

• STEP 8:

The last step is to arbitrate the working pressure of the hydraulic system. Despite enormous selection of hydraulic cylinders out there, most of the hydraulic applications work at 2500 – 300 PSI pressure. This pressure rating is sufficient to perform most of the hydraulic applications. Exceptions in pressure would be such applications as excavators, hydraulic presses, hydraulic jacks and other heavy-duty mining equipment which work at 4500 – 7000 PSI pressure.

These basic 8 steps will help you to evaluate and properly measure a hydraulic cylinder you currently have. When you have all these dimensions ready, just give us a call or send us an email (pictures preferred) and one of our customer service representatives will be more than happy to assist you in selecting a proper replacement hydraulic cylinder.