Get in touch today to discuss your requirements
Call: (+44) 01452 523352
In hydraulic systems, a cracked piston-pump or motor housing is something that is considerably more common than many engineers imagine.
Usually this situation is caused by a case-drain line that is either restricted or blocked; sometimes the case drain line is not even attached. In this particular scenario, the pump or motor housing is transformed into a pressure vessel, something that it’s not designed nor intended to be. In fact it’s likely to just go bang! In addition blocked filters can also restrict the drain line and can also lead to cracked housing.
However, you wouldn’t be held to blame for thinking that a cracked hydraulic piston housing would be caused by a failure in the pumps rotating group. Although, in reality, this is something that will rarely occur.
Connecting a flowmeter to measure the internal leakage of a pump or motor case drain line can achieve the same effects if you omit to set the loading valve to the open position. The housing will fail very shortly after starting-up. It’s not a joke, it has happened before and it’s not something that you will want to have to deal with.
Hydraulic systems don’t work well with too much pressure
If there is leakage that surges inside the pump or motor case, and the filter will not allow it to escape, the pressure can be far too much for the housing – resulting in a crack. It may even blow out its seal. Even if this doesn’t happen, there is likely to be some form of mechanical damage from the high pressure.
There are a few issues with pressure, not just cracking but these results can occur too:
· When there is high case pressure, there’s likely to be excessive load on the shaft seal lip. This can lead to a groove wearing in the shaft and then leakage occurring. However, if the pressure is very high then it’s more likely that there will just be complete failure, without oil there will be inadequate lubrication and it will all go horribly wrong.
· The piston-ball and the slipper pad socket will be affected by high pressure on axial piston pumps. The slipper may even separate from the piston, the failure resulting from this can be catastrophic.
It’s very important to install the correct type of filter in hydraulic systems. For example, putting a depth filter on a drain line would not be a good idea and is not recommended.
As we sympathise regularly with our readers, running hydraulic systems can be very costly. Not only can costs build rapidly from replacing damaged or worn components, but there is also system downtime to consider and to add to the expense.
If there is one deadly enemy for hydraulics, it’s contamination. In fact, contaminated fluids can be connected to more than 80% of all hydraulic failures. This includes all the related failures that can result including those of hoses, fittings, pumps and valves.
In fact, there is such a strong correlation between contamination of fluid and the lifespan of components that manufacturers of hydraulic and filtration products actually publish charts with the consequence predictions of not having inadequate filtration installed. Those systems that undergo rises in pressure will suffer from even more damage as contaminant particles make their way around the system.
Unfortunately the particles involved in hydraulic system contamination are usually far too small for the naked eye to see them. This is why it’s essential to use instruments specifically designed for contamination monitoring, otherwise a high system reliability cannot be expected to be maintained.
Although the operators and engineers who take care of industrial hydraulic systems are well aware of this problem, it’s only really coming to the fore of the mobile hydraulic system now. In this microcosm of the hydraulic world, there is still some time-based fluid maintenance going on. However, it’s becoming more apparent that this and spin-on filters are no longer enough to keep mobile hydraulic systems operating at their peak performance levels.
Quantifying contamination in hydraulic systems
Ideally every hydraulic system should have absolute filtration to capture both micro particles and those that are larger.
A Beta ratio of filtration will usually capture 99.5% of all particles that could contaminate a system. Alternatively the 1000 measurement will capture 99.9% of the particles. This will support the hydraulic system in enjoying a maximum service life. However, in addition to the Beta ratio, there are other considerations to ponder over when looking to keep the system clean.
How much dirt a filter can hold and how stable Beta ratio is will determine how well the filtration works out for the system. The best filters are usually cartridge-type that use a number of layers to help to maximise performance for all areas. Each layer will help the filter to either capture the dirt, hold it or to deliver the beta stability.
Another unexpected benefit of the cartridge-type filters is their ability to reduce how much loss of fluid there is when the filter is changed. This can keep go towards keeping costs down, whilst also lowering the impact on the environment. Although the cartridge type filter may cost more to buy, they deliver when it comes to protecting the system and cutting back on fluid loss.
With industrial hydraulic applications, cartridge filters are now considered to be the standard. They are also becoming more popular and widespread in the mobile market, which is becoming more sophisticated when it comes to components in addition to enduring rising costs.
Mobile Filtration Challenges and Solutions
Another area of concern with mobile hydraulic systems is that of space in the system to add filters and other components such as sampling valves. Quite often manufacturers will produce tank-top filters that can be integrated into the hydraulic reservoir, but sit out of the way. With global emission requirements becoming tighter, this trend is likely to accelerate in the coming years.
One issue that is unique to the mobile world is that of the cold start. It’s well known that any hydraulic fluid will thicken when sat at lower temperatures. This can increase the pressure drop for the filter element. The performance will take a downturn until the fluid begins to gain temperature and reaches the operating temperature level. Quite often the comment from an engineer will be ‘I started up and when I hit the level, nothing happened’.
Although it’s possible to install a large filter, it can add to the bulk and the cost of the system. Another work around is bypass the filter by adding in a pressure relief valve until the fluid is warmer. However, this can send contamination downstream. An approach that is less troublesome is to return the fluid to the reservoir as opposed to allowing it to circulate throughout the system.
In summary, as an engineer, the best move you can make is to identify and implement a fine filtration strategy that will enable your hydraulic system to run at its ultimate performance.
When replacing hydraulic fluid, it is tempting to believe that the new oil will be clean and free of contaminants, and that it can be put straight into the reservoir without any problems. Unfortunately, this is not always the case. If you use hydraulic oil from a large drum, there is a high chance that it already contains some water and dirt particles; new hydraulic oil typically has a cleanliness level of ISO 4406 23/21/18, which is more than most hydraulic systems will tolerate. If the system has a rating of say, 20/18/15, then the new hydraulic oil is already too contaminated, as a single digit increase in any of those numbers is effectively a doubling of the contamination level for each micron size.
We can see, therefore, that it is a good idea to filter new hydraulic oil before it enters the system taking with it contamination that will potentially lead to problems with the system. Most hydraulic system failures can be traced back to contaminants in the oil causing friction, high temperatures and a loss or build-up of pressure that can cause serious damage to the components within. Avoidable problems should not be encouraged by cutting corners when replacing hydraulic fluid as it is a false economy.
If you usually replace the hydraulic oil straight into the reservoir, you can add a filtration cart or a kidney loop system to clean the fluid before it gets into the system itself. Even if you have a filter downstream it is a good idea to still keep a filtration system in the reservoir too, to ensure that the downstream filter does not have to work too hard and retains the lifespan it is expected to have, cutting down on element changes. A kidney loop system is ideal for filtering hydraulic fluid in the reservoir and runs independently of the equipment itself, meaning it can still be cleaning the oil even when the equipment is not being used. This means that the fluid can be filtered thoroughly before the machinery is switched back on and also offers a higher level of filtration throughout the life of both the hydraulic fluid and the equipment itself.
Dual filter elements are usually used in kidney loop systems to filter out particles of different sizes and ensure that the filter does not become clogged too early. This also allows for better element change schedules as they can both be done at the same time, rather than replacing the first, then the second, then the first again and so forth more frequently. The dual filter elements in a kidney loop system also perform better than in-system filters, as they are not exposed to any pressure and can retain contaminants more effectively.
Alternatively, new hydraulic fluid can be filtered into the system via the return filter. If the application is very sensitive, it may be best to stick with a kidney loop filter, but if this is not possible due to the nature of the hydraulic equipment, the return filter route is a good option. A tee needs to be installed in the return line above the filter, and one branch connected to a drum pump discharge hose via a quick connector. When it is time to filter the new oil in the drum pump, it is attached to the return line and the oil gets pumped through the return filter and into the reservoir.
Not filtering new hydraulic oil into a system basically opens the door wide to dirt and water getting in, and undermines maintenance activities and careful user behaviour designed to keep the equipment in full running order. If you need to change how you replace the hydraulic fluid or add a filtration component into the system, the cost of doing so should be weighed against the savings in unnecessary maintenance and repairs due to contamination related damage.
This article focuses on the common problems associated with hydraulic systems and how these issues can affect individual components as well as the systems themselves. It gives an in-depth insight into how problems initially develop, any knock on effects and how failures can happen if the issue isn’t diagnosed correctly.
Abnormally high fluid temperatures
High fluid temperatures are usually caused when the system struggles to correctly dissipate heat and can lead to increased heat load. When fluid temperatures exceed 180°F (82°C), this can lead to damage to the seals and in turn start to degrade the fluid itself.
When viscosity levels drop below optimal values for the system components, the fluid temperature is judged to be too high and the reservoir should be checked for any obstructions or blockages.
The heat exchanger is another component that should be checked making sure the core is not blocked. In order for the heat exchanger to successfully dissipate heat, the flow rate of both the hydraulic fluid and cooling air/water should be at the correct levels.
When fluid circulates to areas of differing pressures without correct pressure correction, excess heat can be generated and any areas that show signs of internal leakage can increase the heat load on the system. This includes anything from a leaking cylinder to an incorrectly adjusted relief valve.
High fluid temperatures can also have an effect of components as they go through a thinning process which affects the oil film, otherwise known as a low viscosity which leads to inadequate lubrication. This issue can be tackled by setting up a fluid temperature alarm to warn of dangerously high temperatures.
When a machine starts to show signs of reduced performance and functionality this points to a problem with the hydraulic system. A loss of speed in the system is usually caused by a poor flow rate and can be noted when the system takes longer to cycle or is slow in its general operation.
Leakage is a common cause of slow operating speeds as flow can escape from hydraulic circuits. This leakage can be either internal or external with typical candidates being burst or degraded hoses or leakage from pumps, valves and actuators.
A useful tool to measure leakages and pressure drops is an infrared thermometer which can identify components with internal leakage. So going by the manufacturers limits for correct temperatures, the thermometer can pinpoint potential problems. Incorrect hydraulic oil out of manufacturer specification can also lead to pressure changes and a decrease in system performance. A successful infrared test will also pick this issue up.
Sometimes, under extreme operation, overworked machines start to overheat. Using the correct oil viscosity will help to alleviate this issue from occurring in the first place and avoid costly failures by lubricating the system effectively. It is also important to let the system prime itself before use thus ensuring all important components are lubricated correctly and to manufacturer standards.
Abnormal and irregular operative noise
Abnormal or irregular sounds while the system is operating are good warning signs of a potential problem either currently occurring or about to occur.
There are two main candidates that attribute to this problem – aeration and cavitation. Aeration is a condition where too much air enters the system and contaminates the hydraulic fluid within. This commonly leads to a loud banging or knocking noise from the system when it compresses and decompresses whilst the fluid circulates through the system. Actuator movement can also become erratic and the fluid degradation can eventually lead to damage to seals through overheating.
Cavitation commonly occurs when a hydraulic circuit demands too high a level of fluid than is being supplied at any given time. This in turn causes circuit pressure to fall below the level of vapour in the hydraulic fluid. The knocking sound that comes from this is caused as the vapour cavities implode during compression.
Both these issues can cause component or system damage with extreme cases of cavitation being known to cause metal erosion and failure of system components.
Providing all the necessary diagnostic tools to a hydraulic system technician almost guarantees that the source of an issue will be discovered and remedied rapidly. However, as with any ill, prevention is better than cure. Using the diagnostic tools on a regular basis can identify any trends that could result in the failure of a component.
Hydraulic system fluid contains many answers
Quite often, it’s the hydraulic fluid that reveals the answers as to where potential problems will arise. For example, taking a fluid sample can provide a multitude of measurements including how much of the following are in the fluid in addition to any signs of oxidation which is typical of being subjected to too much heat:
There are some tools which can make taking samples easier such as a ply and sampling valve. It also means that you won’t further contaminate your machine by adding more contaminants to it.
The value of sampling fluid regularly twinned with the fact that hydraulic equipment is usually caked in some form of dirt or dust, does not make an easy marriage. It’s essential to keep that dirt out of your system and your sample. Engineers know that sampling from hydraulic systems is a risk that engineers have to take. It’s a risk to take the sample as there is a good chance that something from the surrounding environment could enter either the system or the sample. Nobody wants dirt, particles or even water in their hydraulic system.
The risk increases when it’s necessary to draw the fluid from the hydraulic motor. Unfortunately a tube must be inserted through an open port that is accessible once an access plug has been removed. This makes it possible for contaminants to enter the system or even to stick to the tube and then be inserted directly into the fluid.
Of course, being careful will prevent contaminants from entering the hydraulic system, but it’s very important to be very careful, otherwise the fluid could be compromised.
If the environment that you keep your hydraulic system in is far from clean and dry, then you may prefer to use a sampling kit. It cuts down on the potential for contaminating the hydraulic fluid. It is not funny when you go out of your way to ensure that everything will be ok, but then realise that something must have gone wrong when you find a large particle in the system.
The sampling system is inserted into the access plug that the pump came with. Once the plug is in place, then I won’t protrude more than 1 inch, which makes it a very easy system for those who are limited to smaller space.
Then once the tap is in place, it’s easy to just unscrew the cap which will expose a cavity where you can easily take a sample from. There is then a sampling probe which will connect to the sampling valve. You’ll then find a length of clean sampling tube that connects to the vacuum pump and a clean sample bottle. Just pull on the handle to draw out fluid for adding to the sample bottle.
Taking clean samples is essential in order to take a balanced view of what’s going on with any hydraulic system. It’s possible to attain this by using one of the sampling valves that are available on the market. They create a closed loop circuit which will prevent any contamination from entering the oil sample. The sample can only be taken once the probe is fully engaged with the valve. Once the sampling probe is disconnected the sampling valve will reset.
By taking clean samples, you can discover what is going awry with your hydraulic system, and even predict potential future issues. However, if it’s not clean or you introduce further outside dirt or muck, then it’s not going to be at all helpful and you’d be better off not doing it at all. Ensure that you keep your sampling clean to promote the ‘health’ of your hydraulic system.
Hydraulic filtration is a vital component of keeping a system running smoothly.
For example, did you know that up to 75% of failures with fluid power can be attributed to contamination? With the use of hydraulic filters, contamination damage can be significantly lowered which can not only cut down on expense but lower that 75% drastically.
If you’re looking to save costs from less downtime then it’s also time you looked into what a difference hydraulics filtration can make for extending the life of your equipment. Running your system optimally is essential when it comes to cost saving, but protecting its longevity is also a critical element in running any business efficiently.
Muck and dust can destroy a hydraulic system, that’s why it’s essential to make the best use of hydraulic filters. You wouldn’t even be able to remove that dirt yourself, as it’s likely to be dust that is so fine that you won’t be able to see it without the use of a microscope. Dirt has the same detrimental effect as sandpaper or gravel and not only will generally deteriorate the system, but it could even destroy it.
However, through the use of a hydraulic filter system you will be able to maintain control over the level of contamination and by doing so reduce the failure of systems by as much as 75% just be removing that dirt.
Hydraulic parts are expensive. Combine that with down time and having to keep engineers on hand to fix worn components and that’s a lot of expense to deal with. Putting filters into place can even save costs by increasing how long the hydraulic fluid will last.
Degradation of fluid – hydraulic fluid that contains fine metallic particles can degrade rapidly through chemical breakdown. Without protecting against this, there could be issues such as slippage, internal leakage, corrosion or sticking parts.
Scoring of surfaces – this can occur when particles get trapped between surfaces of seals
There’s no doubt about it, but …
· System performance is affected by dirt levels
· Hydraulic filters can control levels of dirt. Without using this management method, the system will get dirtier and dirtier until it fails.
In fact, hydraulic filters are the only way to control how much dirt is in fluid. Without them you will be forced to change out the hydraulic fluid regularly, which can be a time consuming and costly event.
Hydraulic system dirt particles are incredibly small. In fact, they are so small that they cannot be seen by the human eye – and 98% of hydraulic fluid has some dirt in it.
Engineers have found that when it comes to size of particles in samples taken from operating systems, the smaller the particles, the more dirt there is in the system.
So where do these particles come from that we have to work so hard to deal with?
In order to have an idea of what goes on inside the closed system, let’s examine where these particles come from.
Instead of enjoying the typical 20 gpm that is the measurement of a pumped flow from a 2000 psi system, you can expect to see something in the region of just 10 gpm. Although your pump will still produce for you, you’ll discover that the degradation results in just 50% efficiency and you should als be prepared to experience extra heat and other unwanted issues.
As with any hydraulic system, there is an optimum level of cleanliness, but there is a point where you cannot get any better performance out of the system by improving the quality of the fluid. However, with the use of hydraulic filters you should be well set to extend the life of your machinery.
Electrostatic charge builds when there are two bodies moving and creating friction. The fact is that this also occurs in hydraulic systems from the friction caused by system components with moving fluid.
Although we haven’t had a lot of situations that have involved electrostatic discharge, it is still something that every engineer should be aware of.
When an electrostatic discharge occurs, there is a clicking noise as charge increases and is then released. This is something that will often occur in a filter – leaving burn marks and potentially other damage.
With the increasing preference of using non-metallic additives in hydraulic oils the electrostatic charge could be on the increase. Those hydraulic oils that contain anti-wear additives that are zinc-based have considerably high conductivity.
Conductivity in hydraulic oils helps when it comes to moving electrostatic charge around the system. Although zinc-based additives will rarely collect enough charge to cause a big problem, synthetic oils can. This is because they have less conductivity and therefore will potentially accumulate more charge before discharging it.
Another change that could lead to an increase in electrostatic discharge is that there has been a change made to the materials that filter elements are made of. In order to make them easier to dispose of them in an eco-friendly way, they have more non-metallic material in the design, which lowers conductivity and therefore increases the capacitance.
The manufacturers of hydraulic filters are aware of these issues, and are looking into how they can minimise or even eliminate these issues.
However, if you come across a situation where there is electrostatic discharge in the meantime, then consider this:
By adding larger filter elements you can reduce flow density and therefore the amount of charge that is being generated. You might also want to consider increasing the tank size so that the time between charge generations increases.
This is one of the reasons why you shouldn’t skimp on tank size or on filter capacity.
Hydraulic Power Pack
Connect with us
Connect with us on social media or eBay