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Regular hydraulic cylinder maintenance is crucial to the upkeep and performance of your system
Service Code : KHP 06

Here we share our top tips for successful hydraulic cylinder maintenance.

1. First things first - keep your hydraulic oil clean

Many hydraulic failures occur because of hydraulic oil contamination. This is important to prevent damage to your system and components. If hydraulic oil is contaminated, it must be thoroughly cleaned as soon as any contamination has been found. It is also best to fit high-efficiency filters and change them when necessary.

If a filter has a build-up of debris, a differential pressure gauge can be installed to give you a good indication as to when they need to be changed. This means that you will be preventing a bypass, where the oil flows through the system unfiltered.

2. Undertake regular maintenance

Regular maintenance on your hydraulic cylinder is important for optimal performance. Make sure you keep a close eye on the condition of the cylinder rod for any signs of corrosion, pitting or wear. Too much moisture can cause corrosion; whether this is from the air or from within the hydraulic fluid itself. If water contamination occurs within the fluid, it can cause major failure of the component or system - the oil therefore needs to be thoroughly cleaned as soon as possible. Corrosion also encourages wearing of the seals, due to increased friction; pitting causes a similar problem.

Misalignment is often the main cause of uneven wear within a cylinder. Premature wearing of the bearing seals and rod can be caused by side loads allowing the rod to rub on one side of the bearing. Hydraulic cylinder maintenance here can often be as simple as a re-chrome or polish to repair a corroded or damaged rod. If a cylinder rod is beyond repair, a replacement is the best course of action. However, before you re-install the new rod, it is important to first remove the problem that originally caused the damage and make the new cylinder more cost-effective.

3. Rotate or alternate cylinders

As with other hydraulic components, if the risk of downtime is not an option, it is always a good idea to hold another cylinder(s) either as a ‘critical spare’ (see below) or that you can alternate usage between regularly. This break between uses keeps the cylinders in good shape, despite possible particle contamination and harsh operating conditions. It is also wise to undertake maintenance on these cylinders when they are removed from the system, so that they can be repaired if necessary.

Before re-assembling a cylinder, you may want to first replace all of the seals. Inspection of the cylinders may also give you an idea as to the condition of the entire system. For example, if there is a consistent varnish throughout your system, it could mean that the oil temperature is too high and it needs to be altered.

4. Maintain your cylinder accessories

Each separate part that makes up your hydraulic cylinder is just as important as the cylinder itself. For example, if a pivot pin or clevis is worn or damaged, this could cause slop and play within the joints of the cylinder. This leads to misalignment and wear or more permanent damage.

*Critical spares analysis – an analysis of system critical hydraulic components and recommended spares; so that you can understand which of your hydraulic components are most susceptible to failure and the impact that this may have on safety, production and systems performance… and just as importantly the cost and lead times involved in sourcing replacements.

Hydraulic Cylinder Testing

Hydraulic cylinder testing is crucial in order to maintain optimal performance.

In testing, measurements of any leakage need to be taken and to do this, the typical method is to pressurise the cylinder at the end of stroke. This hydraulic cylinder testing technique is known as the ‘end-of-stroke bypass test’.

The only major disadvantage to this test is that, as the name suggests, the only seals tested are the ones at either end of the cylinder – where there isn’t a lot of deterioration of the component. Realistically, the centre of the tube is most likely to be prone to more damage, therefore that’s where the test needs to be performed.

In a double-acting cylinder, a ‘mid-stroke bypass test’ is a suitable method to test the piston seals. One of the issues with this technique is how to control the cylinder; a hydraulic engineer has to hold the component mechanically to keep the cylinder in the centre. Even a smaller sized cylinder can generate 6 to 10 tonnes of force, so this method is very dangerous. With larger cylinders, this task is impossible.

The only test that is appropriate for this is something called ‘hydrostatic testing’. This is a test that is performed after the piston has been held hydraulically in any position that is required. The pressure intensification that is created helps to keep the piston in one position along the entire cylinder to make sure that all the seals are functional and there is no leakage. The only consequence this might have is if the pressure is allowed to build up at the piston end of the cylinder with the valve closed, the pressure at the rod end will to too great, which could cause disastrous failure.

  • Ensure the cylinder is secured so that it is controlled;
  • Clean hydraulic fluid must fill both sides of the cylinder – do this through the service ports;
  • Connect all components – directional control valve, relief valve, ball valves and gauges;
  • Remove any air from the cylinder by using the directional control valve and stroking the cylinder numerous times;
  • Place the piston rod mid-stroke and close the ball valve;
  • Direct the fluid flow to the side of the cylinder where the rod is located;
  • Increase the setting on the relief valve until the pressure of the cylinder is seen on the gauge;
  • Close both the ball valve and the directional control valve;
  • Record the pressure of the cylinder from on both gauges and keep an eye on any changes.

Our hydraulic cylinder maintenance

A hydraulic cylinder repair is a relatively simple process, as they are less complex than other hydraulic components; in many cases a well-repaired cylinder is indistinguishable from a brand new unit. We offer a hydraulic cylinder maintenance, in addition to repairs on pumps, motors, power packs and other types of hydraulic equipment.

Internal and external leaking is the most common reason for repairs on hydraulic cylinders. But, by disassembling and closely inspecting the damage to the cylinder, you may be able to see other problems that aren’t immediately obvious.

Our service includes a free assessment, where we will strip down your faulty unit and diagnose the full extent of work needed – providing a quotation and details of how many parts can be salvaged. We may conclude that a repair is not viable, or that your repaired equipment may be unreliable or prone to poor performance in future. If this is the case then we will always contact you to explain why and to quote for a replacement new unit so that you can choose what you want to do.

When assessing your equipment our team may also be able to provide recommendations on how to improve your system’s design and efficiency, allowing you to reduce running costs and minimise the likelihood of any future downtime and hydraulic repair work. We can also undertake a “critical spares analysis” identifying those key system components that we recommend you hold as spares.

There different types of hydraulic cylinder repair

Piston seal

the piston seal can become defective if it is distorted, eroded or missing and this is usually a cause of an oversized barrel or bulge during operation. At this point, replacement of the barrel or cylinder is required. If you replace the piston seal only and not the barrel, whilst this is a quicker method of repair, it is a short-term fix. More maintenance would be required later on.

Rod seal

A distorted rod seal can be caused by excessive wear of the guide bush or if the rod is bent. The consequence of this is the rod weight pushing on the seal, causing failure. If you replace the rod seal without identifying and correcting the underlying issues, then again, the fix will only be short-term.


In most cases, the chrome on the rod can be inspected and if it is shiny on one side and dull on the other, the rod is bent. The straightness of the rod should always be checked when repairing the cylinder. Bent rods can be corrected by using a press. Whilst it is possible to prevent damage to the hard-chrome plating during this process, if the chrome is spoiled, it must either be re-chromed or the entire cylinder must be replaced. A damaged chrome surface decreases the efficiency and service life of the rod seals. If the rod only has some minor scratches, they can be polished out using fine emery paper.


In light-duty applications, pistons within the cylinders are designed with aluminium or cast iron, and are in constant direct contact with the cylinder bore whilst in operation. Some scratching on the outer surface of the piston poses no risk to the cylinder’s function, as long as the nominal bore diameter does not exceed the minimum diameter of the piston. A good tool to use to check the length could be a micrometer.

Taking the necessary precautions for safe hydraulic cylinder storage

Prevention is better than cure. Fact. So here are some tips to help ensure that your hydraulic cylinder storage procedures are up to scratch:

When you store your cylinders, keep them in a clean, dry area, and preferably indoors wherever possible – even if you think your cylinder is too large or long for indoor storage. Really try to find or create the space somewhere – it will be worth it in the long run!

Keep all of the exposed metal covered and protected. The internal surfaces of the cylinder can be smothered with grease, while a special tape, that has been infused with oil, should be wrapped around the exposed chrome on the rod. The rod must be retracted before the tape is applied though, if not the tape could damage the rod seal.

If there is no oil in the cylinder, it will most probably have been replaced by air. Problems then arise if the air isn’t dry and the environment temperature decreases and reaches dew point, causing moisture to form inside the cylinder. This, in turn, could lead to rust and pitting, which can cause serious issues if the cylinder is in operation. Not only does it decrease the effectiveness of the cylinder, but it can also significantly reduce the life of the cylinder.

If you thoroughly clean the inside of the cylinder and then fill it with clean oil, this problem can be avoided, but care must be taken due to the ambient temperature. This depends on when the cylinder is put into storage and then taken out again to be installed in a system. For example, if your hydraulic cylinder storage takes place over winter, and it is then taken out again to be reinstalled in the summer, the ambient temperature of the oil in the cylinder is going to change. Oil can be filtered into a cylinder during storage if you take the following precautions:

  • Ensure that the temperature changes within the environment won’t have the outcome of static pressure that surpasses the operating pressure of the cylinder;
  • Only put oil in the cylinder when it has been fully retracted and through the rod-port. By doing it this way, you avoid a hazardous pressure increase;
  • Service port plugs or blanks are good to use and they are rated for the operating pressure of the cylinder;
  • A warning needs to be placed at each service port;
  • Make sure that there is a way of checking and release any pressure before these services port blanks are detached.

Finally, make sure that the cylinder doesn’t experience any pressure intensification when exposed to alternating temperatures once being installed onto a system after a long period of storage.

About hydraulic cylinder seals

Hydraulic cylinder seals are commonly found in applications where components are exposed to liquids.

They play a vital role within the hydraulic system, as they enable the transfer of liquid power into linear motion. The hydraulic cylinder seals are manufactured from a variety of materials including rubber and polyurethane. Known for their durability under appropriate application settings, these seals can, however, fail or cause serious problems / damage if settings are not correct. Oil contamination, high temperature, chemical erosion or inadequate installation can all cause hydraulic cylinder seals to fail leading to damage in the wider system.

Oil Contamination

contamination within the system is a main cause for the hydraulic cylinder seal failure. Hydraulic oil contamination increases the risk of internal leakage as well as reducing the control of flow and pressure in valves, which could eventually waste horsepower and overheat.

Contamination can form from hydraulic oil, environmental exposure, system wear, the manufacturing process and servicing. Contamination can get into the system when the rod retracts, so it is best to consider the installation of a rod wiper. If hydraulic oil is filtered appropriately, this oil contamination can be prevented. If you start to notice a scratched rod and cylinder surface, extreme seal wear and an oil leak, it may be the result of contamination and your oil needs to be thoroughly cleaned as soon as possible.

High Temperature

If hydraulic cylinder seals look hard and brittle, or the seal lip or body is eroding, the temperature of the oil in the cylinder may be too high. High temperature for a long period of time may result in the seal losing functionality, either by excessive compression or damage to the seal material. This could be due to the seals not being manufactured with the right materials, too much friction or close proximity to the source of heat.

Chemical erosion

If the inappropriate material is used within the hydraulic cylinder seal, it could lead to a serious chemical breakdown, or could change the compounds of the oil altogether. This causes chemical attacks from the additives in the oil on the non-compatible material which can reduce the seal’s elements. A result of the chemical breakdown is the loss of the seal lip or too much swelling or shrinkage. A more obvious sign of a chemical breakdown can be discolouration of the hydraulic cylinder seals.

Inadequate installation

One of the main reasons for hydraulic failure is inadequate installation. It’s vitally important that when you are installing a seal that: the equipment must be thoroughly cleaned, the hydraulic cylinder seal cannot be damaged by scratches and that the entire system is sufficiently lubricated. If the seal gland is too tight or a gland is obstructing a seal lip, this could also cause problems. A seal that has been installed upside down can be avoided through care and attention during installation.

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