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There are a number of reason why hydraulic cylinders fail ranging from misuse to bad specification to old age. Here are the most typical reasons why they fail:
The most common reason for an issue here is because the seals do not fit correctly. Another problem can be corrosion or abrasion of the seal grooves. If the oil is possibly contaminated or there is trapped oil, this should also be considered.
Piston rod scored
Oil contamination can cause a lot of issues, one of them being the scoring of the piston rod. However, keep an eye out in case there is contamination of the gland bearing as this can lead to gland bearing failure if not caught in time.
Cylinder bore scored
Contamination of oil can also wreak havoc by being the cause of scoring the cylinder bore. This can even turn out to be piston head bearing failure. Flushing of the system can help with this.
Barrel internally corroded
Water in the oil is usually the cause of the barrel suffering from internal corrosion. Start with changing the oil and there may be a need to disassemble and recoat.
Piston rod pitting
Corrosion can also cause piston rod pitting. It may also be a sign that there is a wrong specification of the cylinder or perhaps the environment in which it’s being used is not what it was designed for.
Bent piston rod
This will quite often occur when there is an overloading of the hydraulic cylinder. This could be due to the cylinder and piston being used in a way that is not in alignment with their specification. It may also be caused due to a sideways impact from outside, perhaps from a collision.
Generally speaking, most engineers find that contamination and corrosion is at the heart of the majority of hydraulic cylinder failures. This is why it’s essential to protect your hydraulic system from moisture and oil contamination.
Are you interested in what can cut costs when it comes to Hydraulic Power in your business?
We can only imagine that the answer is ‘yes’ as most of us are. Well, we’ve got some good news for you. Today, we’re going to look at what the most common reasons are that hydraulic components fail, even those that have not been in service for long.
These points are worth making a note of:
1. Oil changes. It’s not necessary to keep changing the oil unless you have one of thes2 following conditions occurring.
The oil has degraded so far that the original additives have changed its makeup. Changing oil just because you feel it’s about time it’s changed is going to cost you a lot of outlay as oil is expensive. The larger your reservoir, the worse off you’ll be. However, if you keep operating your system with degraded oil, then that could cost you even more. Even changing the oil based on how long it’s been in service isn’t going to help. Oil needs to be analysed to fully understand its condition.
If you discover that your oil is contaminated with particles, the more economical manner to deal with this is to remove the particles through filtration.
So in summary, only change the oil when the additives have been depleted and the base oil is useless. You will have to perform oil analysis to make your decision.
2. Filter changes. It’s the same story with hydraulic filters. Changing them based on hours in service could mean that you’re too early or even too late. Early brings about waste as their capacity is not reached and you’ll be throwing away an unused amount of filter time. Changing them late is also an error as the particles will not be removed from the oil and therefore, it could lower the lifespan of each component in the entire hydraulic system.
The most effective approach is to only change filters once they have become full of dirt, but prior to the bypass valve opening. This may require a mechanism to be added that will monitor the pressure and deliver an alert when a point is reached. A clogging indicator is one of the most basic methods of handling this. However, continuous monitoring of pressure drop through the use of a differential pressure gauge or a transducer is the optimal solution. In summary, changing filters on hours is not maintenance effective, or cost effective.
3. Heat. If you’re driving along and you notice that your car engine is overheating, you would most likely stop. Most equipment owners won’t run an engine that is overheating. They know it’s going to cause problems. However, the same cannot be said about operators of hydraulic system.
Just as with a car, running an overheated engine is the quickest way to destroy hydraulic seals, hoses and other components. How hot is too hot? The answer depends on the viscosity of the oil in addition to the hydraulic components. Viscosity lessens with increasing temperature, so the answer is when the temperature is high enough to stop the oil lubricating as it should.
When it comes to hydraulic components, it’s worth noting that a vane pump needs more viscosity than a piston pump would. If you have a vane pump in your hydraulic system, then you’ll want at least 25 centistokes to be maintained.
Temperatures over 82°C will cause damage to seals and hoses in addition to accelerating the oil’s degradation. Never allow your hydraulic system to operate above 82°C with a viscosity lower than 10 centistokes.
4. The wrong oil. The most important element of any hydraulic system is always the oil. It’s what keeps everything lubricated and it is also what transfers the power. With these two major tasks to handle, keeping an eye on viscosity is a must.
The viscosity of the oil is what will determine the temperature at which the system should be run. You may have heard this referred to as temperature operating window or TOW. A temperature that is too high will prevent the oil from flowing or lubricating as it should. Oil that has a viscosity that is too low will not deliver adequate lubrication either. Keeping an eye on this will also ensure that you power isn’t lost due to either internal leakage or mechanical friction.
You don’t want increased power consumption as it will cost you more. The best way to handle this is to check what your machines temperature operating window is and to ensure that your machine operates within that window at all times. We won’t go into how to do this here, as it’s rather complex, but it’s something that does need to be addressed.
5. Filter locations. There are two locations for filters that cause the most problems – the piston pump and motor case line and the pump inlet. You may have a strainer attached to the pump inlet to collect any ‘garbage’ in your oil, but this oil is being drawn from a reservoir, not somewhere where there should be any garbage.
The pump inlet is also positioned off the bottom, so there should not be a lot of dirt passing through. By placing filters here, it can affect whether you get maximum pump life. If there is any form of restricted intake, it can reduce the lifespan of the gear pump by as much as half. Hydraulic pumps are not built with ‘sucking’ in mind! The way to handle this is to remove any suction strainers or depth filters on either the pump inlet or the piston pump.
Applying these points should be helpful to any hydraulic system operators and should deliver methods to save yourself and your business great expense.
Until next time..
If you’re curious about how hydraulic cylinders work, then you could find this post to be interesting. Let’s take a look at these powerful components that make it possible to move and lift the heaviest of items with ease.
You may not have ever considered this before, but what do you think deploys those huge wheels that aircraft need to land? They are put away tidily throughout a flight, and then when they’re approaching Heathrow, out they pop and all at the pilot’s press of a button.
Landing gear is operated through a hydraulic system. As with any hydraulic system, there are pipes, cylinders and of course hydraulic fluid. The fundamentals of this are the same as with any hydraulic system. When force is applied at one point, it is transmitted to another through the use of incompressible fluid.
Hydraulic cylinders mostly come in parallel pairs that are of differing diameters and are connected by a pipe. The cylinders will be at right angle to the pipe. This arrangement is then filled with a hydraulic fluid such as oil until the cylinders are partly filled.
The space that is left in the hydraulic cylinders will enable the pistons to operate. In one cylinder, the piston will be smaller than in the other. Fluid will be pushed into the chamber of the small piston and when force is applied, it will push the fluid into the chamber of the big piston as it will be incompressible fluid. This will then move the big piston. Due to the difference in size, the effect of the small piston’s movement will be multiplied. So for example if a small piston has a downward force applied to it of 100 lbs – the force on the big piston will be 900 lbs.
Hydraulic cylinders remove the need for a rigid structure when it comes to transferring force between two different points. This can be used to the hydraulic system’s designer’s benefit and a number of twists and turns can be added to the system. For example, there might be a space constraint. Using the different cylinders at different sizes, it’s possible to create a system that will pull, push or even lift heavy weights.
Although the hydraulic systems that are used in our everyday life are not built with cylinders quite as basic as what’s described above, they are fairly similar. Let’s look at the different components involved:
· Cylinder barrel
· Piston rod
· Cylinder bottom (Cap)
· Cylinder head
· Cylinder bottom connection
· Rod glands
There are two different main types of hydraulic cylinders used. The tie rod type of cylinders and the welded body type. The former are used when there is a need for heavy-duty industrial or commercial use. Some are small bore and others large bore. The welded body cylinder type has no steel rods in it. The top of the barrel of the cylinder is welded directly onto the object that is expected and designed to move. Although these cylinders are small in size, they are used in a surprisingly large number of different machines. In some cases it’s necessary to use a telescoping hydraulic cylinder where the piston rod will retract into the barrel of the cylinder.
Hydraulic power has really evolved over the last 50 years or so. Much of the progress has come from the aeronautical industry, surprisingly. Although hydraulics have been used since before the time of the first recorded history, it’s only now that they have really come of age and have made such a tremendous difference to us in so many fields.
Hydraulic cylinders obviously make up an important part of hydraulic machinery. If you’ve got a lot of machinery, then it’s typical that you’re going to pay out a fair amount on cylinder repair expense.
Researchers have found that failures of design can make up to 25% of mechanical equipment failures. If this is applied to hydraulic cylinders, then it’s possible that as many as 1 in 4 cylinders are not designed adequately for what they are doing.
Even if the cylinder may do the job that it’s been assigned to, it won’t do it with a service life that is acceptable. Here are the main reasons that badly designed cylinders may fail you and what you need to look at to improve matters.
1. Bent Rods
Cylinder rods can bend when the materials they are made of are not strong enough, the rod diameter is insufficient or there is an issue with the cylinder mounting arrangement. Once there is any bend in the rod, it will only get worse when more load pressure is placed on it. This can also result in failure of the seal and increased leakage.
Use the Euler formula to check allowable rod loading.
2. Rod Finish
The life of the rod seal can depend on the cylinder rod’s surface finish. If it’s too smooth, there is not enough lubrication, or if it’s too rough then there will be a lot of leakage at the seal.
In order to extend the service life of the cylinder, treat the rod’s surface with this in mind.
3. Ballooned Tubes
If the cylinder tube wall is not made of strong enough and thick enough material, it could balloon. Once this happens, high pressure fluid could bypass the seal. Couple this with too much heating and the piston seal will come to a premature end.
4. Insufficient Bearing Area
If the side thrust cannot be handled well by the bearing (wear) bands, then the seals could become deformed and therefore have a shortened life span.
With regards to making amends to these issues - you may be able to perform some minor repairs, but if you’re faced with the same issue time and again, it’s advised that you opt for a redesign.
When it comes to hydraulic cylinders, one of the main causes of failure is the seal. Although the cost of the seal may be marginal, the true expense comes from downtime and the loss of production.
To save you this extra expense, let’s look at what might cause a problem with the cylinder that may result in hydraulic seal failure:
The seal has not been installed properly.
There are a number of problems that can go wrong with installing a seal, these include:
· Cuts and nicks in the seal
· Not enough lubrication
· Over tightening
· A seal that has been placed upside down.
The best approach is to be very careful when installing the seal.
Contamination of the hydraulic system.
If any dirt such as grit, mud, dust or even ice gets into the hydraulic system it can contaminate it. There may also be an issue with internally produced contamination such as metal shavings or items results from the degradation of components such as hoses, fluid, etc. However, it’s most common for hydraulic systems to be contaminated from external issues such as rod retraction. This is why it’s important to use good filtering in the fluid system. Once you see a scored cylinder surface or if you see wear on the seal you may need to investigate further.
Incorrect material usage.
If you see a breakdown of the seal, it is likely to be caused by the use of incorrect material. This may also be caused when the hydraulic system fluid is changed. Non-compatible materials are most often the main reason there is failure with the seal.
Degradation from heat.
Once the seal is brittle and hard looking or if you see the seal lip start to break away, then there is likely to be heat degradation. This will result in an issue with effectiveness of sealing. This issue can be solved either by introducing an increase in lubrication, or change the material that the seal is manufactured of.
If you’re experiencing hydraulic cylinder seal failure, then ask the manufacturer for guidance on seal size and for their input into how the hydraulic seal’s lifespan can be increased.
Although using high-pressure hydraulic systems is considered to be one of the safest methods of applying force, there are still some important factors to take into account. They are powerful tools and can take on any bending, lifting, pushing or pulling work that you need performed, but there are some important safety factors that need to be observed.
Surprisingly, one of the weak points of the hydraulic system when it comes to safety is that it is very easy to use. This can lead to complacency and in some cases abuse. As with any type of equipment use, there are rules to be followed and disciplines to observe in order to get the best from these machines whilst keeping yourself and others in the vicinity of the equipment safe from harm. Following these guidelines can also often ensure longer lifespan and greater efficiency of the machinery.
In the following passages we look at the different areas of safety that will need to be taken into consideration when dealing with high pressure hydraulic tools.
Just as with any equipment, it’s necessary to observe standard safety rules. This means that gloves, safety glasses, boots or safety shoes and a hard hat all need to be worn. As in any environment that can be hazardous, these should be considered fundamental necessities.
Although most engineers will take the most obvious precautions to avoid accidents whilst taking the longevity of the equipment life into consideration, most mishaps and issues will come from either not operating the equipment properly or not assembling it in the right way. It’s important to understand each function in addition to being clear how it works. Take time out to learn your machinery and how it works.
Lifting of loads that are over capacity is something that can result in trouble. Not only will the cylinders be at risk of damage but it can also result in bent plungers and blown seals.
Keep in mind the following points:
- Take an estimate of what you think the load will be, then apply a suitable safety factor.
- Keep in mind that some of your pumps will be equipped with relief valves whilst others won’t be.
- The use of a gauge will help to give an indication of which operating loads are safe.
- Your gauge should also be used to determine whether there is any pressure in the system before you make any changes or breaks in the hydraulic connection.
- Check your environment before you either advance or retract a cylinder.
Fundamentally, two types of cylinders are used in hydraulic systems. The single acting and the double acting.
Single acting cylinders may be any of these types:
· Spring return
· Load return
Double acting cylinders work with the use of hydraulics and advance and retract.
It’s important that you follow these safety guideline rules for cylinders:
- If you need to position the cylinder on the ground, ensure that the base is able to bear the weight of it. It wouldn’t be funny to watch your hydraulic cylinder disappear into soil. A jacking based should be used, or at least a steel or timber plate that will enable the load to be spread.
- The saddle should have the load spread across it, and not be point loaded.
- Stay clear of and be careful around any areas that are directly below a load that the hydraulic cylinder is supporting.
- Situate your cylinders in order to give enough clearance space for extension of them.
- Excessive heat is any heat that is above and beyond 65°C. This needs to be avoided otherwise packing will be softened and hoses weakened. If there is heat that is not avoidable, use either a piece of metal or a heat-resistant blanket to protect the cylinder.
- Keep oil connectors clean and wipe any couplers before they are connected. Dust caps are provided for a reason and that’s to keep dust and dirt out. If you choose not to use them, be aware that you’re likely to experience scoring of the cylinder walls and this can lead to the eventual failure of seals.
- Over-extending cylinders should be avoided as not all of them have safety stop-rings installed.
- If you need to add oil to the pump, check whether the cylinder is already extended, if it is be sure not to disconnect them. The trouble with having too much oil in the system is that your reservoir could become pressurised and blow. If it doesn’t blow it will rupture.
Hydraulic Hand pumps
Depending upon the speed and oil capacity of your system, there is likely to be a pump available for each cylinder. These may be power-assisted or they could be manual in nature. Those applications that are lower speed and where it’s necessary to have that added human ‘touch’ will usually have a hand pump. If the application needs faster movement, or the cylinder is particularly large, then it will use a power pump.
It’s essential that the pump valve is suitable for the cylinder. For example, with single acting cylinders, there is usually a pump that has a 2 way or a 3 way valve. This equates to one outlet. When it comes to double acting cylinders you’re likely to find a 4 way valve which means it has 2 outlets. It’s dangerous to use a 2 way valves in combination with a double acting cylinder.
Check the pump reservoir level before using. Fill using the correct procedures if necessary. Remember that pump hoses will shorten when they are filled with pressure, so ensure there is enough slack to handle this.
With regards to power pumps, you can expect to come across one of these types:
· Petrol / Diesel
It’s fairly obvious that hose failure can occur after heavy objects being dropped on the hose cause damage, but it’s surprising how this escapes the thoughts of many engineers. We often hear stories of how something was dropped but then it was a forgotten memory and the next thing the engineer knows, the hose has failed and there has been a hydraulics disaster.
Another strongly recommended tip is that hydraulic equipment should not be carried by the hose. Most of us are well aware of this, but you will need to keep an eye on any young apprentices who are as yet unfamiliar with the norms of operating hydraulic systems. There should also be an eye kept out for any sharp bends in the hose. The internal wire braids can be damaged from this type of event and this will weaken the set up and could result in leaks and at worst a lethal situation.
An essential fundamental when it comes to hydraulic system safety is to check all fittings, hoses and connections to ensure that they are tightened as they should be and that they comply with the amount of pressure that they will need to be able to handle with your specific system.
We generally recommend that hydraulic systems use oil that is suggested by the manufacturer. The system will usually have been manufactured around that oil and the creators know that it will perform best with that particular one. You will need to change the oil periodically. This will ensure that the system does not get damaged by dirty oil. Ensure that hydraulic oils do not touch your skin.
After you have finished using your hydraulic machinery, it’s time to get it ready for the next job. You will need to clean it before storing it. You can do this by wiping it down. You will also need to lubricate any parts that are exposed.
In conclusion, operating hydraulic systems safely entails using the right cylinder with the right pump and the right oil. Although these rules may seem obvious and safe, it’s surprising how many people fail to adhere to them and put themselves and others in danger. Hydraulic equipment is very powerful but it can also be very dangerous.
As we have looked at before, a failure in hydraulic cylinders is quite often related to a seal failure. Although the price of a seal is not particularly high, domino effects can make this a very expensive occurrence. The financial costs of loss of production, engineer downtime and / or calling in engineers can soon add up. It’s for these reasons that it’s important to look at what is causing the failure of the seal first.
The key issues behind seal failure are:
Bad installation of seal. When the seal is installed, the following facts need to be considered as this is something that can easily go awry:
· Is the equipment and the room clean enough to insert the seal?
· Protect the seal from cuts or any damage that may prevent it from working at its optimum performance.
· Lubrication needs to be correct
· The seal gland should not be overtightened.
· The seal must be placed the right side up.
Another primary cause of failure of hydraulic seals. Dirt, mud, dust or grit or even internal contamination through metal chips circulating can have a devastating impact on hydraulic seals. Once hydraulic fluid starts to breakdown it can turn to sludge. Another entry point for contamination is the rod retraction cycle. This is why it’s important to install a rod wiper and why the fluid system needs to be well filtered.
Incorrect material. Seals manufactured with unsuitable materials can lead to chemical breakdown. This can occur due to the changing of hydraulic fluid also. Watch for discolouration of your seal to identify when it’s undergoing chemical attack.
Degradation from heat. Once you see the seal change colour and go hard or brittle then there could be heat degradation going on. This can lead to loss of seal. It could be that you need to change the material of the seal, or even increase lubrication.
Summary. Sometimes seals fail because they aren’t the right size or the conditions for them are not optimal. If you cannot change the conditions, at least ensure that you have the right size seal, made from quality material and you should see some improved results.
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