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Filters are a small but vital part of hydraulic machinery, although serving no mechanical purpose they are integral to the proper functioning of the machine and to prolonging the active life of the equipment and the hydraulic fluid which drives it. The role of a filter is to remove and/or contain particles of contamination and keep the fluid that flows round the machine clear. Any contamination in the oil can cause damage to moving parts further downstream, and this can lead to seizing up of moving parts, corrosion of other parts and costly replacements. When we consider the consequences of not using a filter, the importance of these little items becomes more significant.
There are two main styles of hydraulic oil filter – surface and depth filters. The surface filter, as the name suggests, removes contamination from the surface of the oil and may be useful in applications where gravity feeds the oil through a space suitable for such a filter during operation. A depth filter can be submerged in a reservoir or chamber and will remove particles from the entirety of the body of fluid. Depth filters therefore, are more effective and will retain a larger amount of contamination and unwanted particles before they need to be cleaned or replaced.
The materials used to make hydraulic filters varies, as does the cost accordingly. Glass filters are more expensive but they are more efficient, especially when glass fibres are used in a depth filter. Glass is also non-reactive, meaning it can be used with any type of hydraulic fluid. Metal filters are also reasonably efficient, but they cannot be used with all types of hydraulic fluid, due to incompatibilities between certain hydraulic oils and some metals. Where it is appropriate to use a metal filter there is the option of a magnetic filter system, which works as a depth filter and uses a magnetic charge to attract metal particles that may have entered the fluid system. If the hydraulic equipment is used in metal working and fabrication then the chance of potential contamination being from metallic particles is high; magnetic filters will deal with this contamination while another type of filter can be used to deal with other types of pollution.
Cellulose or paper can also be used to make a hydraulic fluid filter, but these have a short life expectancy and need frequent replacement. They are cheaper than the other types, but could end up costing more in the long run, due to regular downtime for replacement and the potential damage to machinery if they are not replaced often enough.
It may seem like glass is the best choice; despite costing a little more it does the best job and will not need replacing too often. The drawback of a glass filter is actually its strength as well; the superior filtering ability can actually lead to a drop in pressure, in the system, which is usually undesirable. It is especially important, therefore, to check how a drop in hydraulic system pressure will affect productivity and performance if you are considering switching to glass filters from another material type. Consider also whether this drop in pressure is likely to lead to unnecessary adjustments of pressure relief valves, leading to potentially dangerous build ups of pressure elsewhere.
The options of hydraulic oil filters do not end after material type and construction, as there is still the issue of ratings and specifications to contend with. All filters have an ISO 4406 rating, and the lower the code of any given filter, the better it is at removing contamination. Hydraulic filters may also have a beta ratio, which is the ratio of particles found upstream of the filter divided by the number found downstream. For beta ratios, the higher it is the better, and this can also be used to give a percentage for effectiveness.
It is also important to check that the flow rate of the filter is compatible with the flow rate of the machinery it is to be used in; too fast and the filter will not be able to effectively remove contamination, too slow and it could become clogged quickly. The operational pressure of the hydraulic system is also important, as the filter must be able to withstand that force for a prolonged amount of time. The final thing to check is that the filter can be connected to the equipment, so check the port size of the filter and ensure it is compatible with the machinery in the location it is to be fitted.
There is a lot to consider here, but choosing the most suitable hydraulic fluid filter is an exercise that it is worth spending some time on, as it can make a big difference to the performance and lifespan of your hydraulic equipment and save on downtime and replacement costs in the long run.
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..
How well do you really know your hydraulic machine? Do you know what its operating pressure is when it’s running normally? How about its typical temperature? If you don’t know the answer of these two questions, then you don’t know your machine very well and you could be putting yourself into a vulnerable position.
Recently, one of our clients discussed an issue they had with their machine. Although it’s the mobile hydraulic systems that we supply, our clients are involved in all manner of hydraulic machine operations and will often request our input into how to handle certain scenario
Our client told us that he had been having a lot of bother with pump failures. His pumps weren’t even lasting long enough to complete half of the service life that they were expected to fulfill. Of course, our client wanted to know what was going on. He gave us some information about the machine and we looked over his log books for clues as to what could be causing this.
We started at the beginning. We asked him what the normal operating temperature of his machine was. Our client said that he had no idea. So we asked about the usual operating pressure range. Again – he wasn’t sure.
Although the type of machine that our client had displayed this information permanently in the control room, nobody was paying any attention to it. They weren’t reading it or documenting it.
Do you monitor the health of your hydraulic machine by this method? If not, then you should be. It’s important to have a good understanding of your hydraulic machinery.
It’s not difficult information to collect and it’s what will help with analysing any issues with your machine and even giving it some preventative cure options.
How to measure the temperature
If you don’t have an inbuilt thermometer then you might want to use an infrared heat thermometer gun to measure the temperature. Be sure that you use it on the same spot every time. For example, you could put an X on the hydraulic tank, just below the minimum oil level and label it. This will be the position of where your tank oil temperature readings are taken.
Also mark labels for the heat exchanger ins and outs and in two other places that are part of the circuit.
If your system is getting too hot, you’ll have some idea of where this is occurring by being able to measure the temperature on your narked locations.
It really is worth ensuring that you know your hydraulic system well. It will save you time, energy and expense as you are more likely to be able to recognise when an issue is arising and take preventative action.
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.
Do you know how long any hydraulic pump should last? In this industry, using past experience might not always deliver the answers you were hoping for, and are likely to give you answers that are actually no better than guessing.
Disappointingly, there is no dependable approach to determine how long your hydraulic pump will last. Using historical data is perhaps something that will give you the best indicator, but if it’s a new pump and you have no data – that’s where the guessing game beings. Fortunately, there are a number of factors that determine how long any pump will last and using these can give you an estimate that is more informed.
For example, let’s consider your hydraulic system. The type of application it is will make a different to the pump life and so will the temperature. Using pumps that are graded as ‘industrial grade’ will deliver a better lifespan than those that are not. Using auxiliary information can also help. For example, an axial piston design pump has less heavily loaded shaft bearings and therefore are not at a great risk of premature failure.
Of course, roller type bearings in this type of piston design can fail prematurely due to brinelling. That’s why it’s better to use shell-type bearings as they are more like a bushing than a bearing.
Another major consideration is the type and grade of oil being used. If it’s ‘special purpose’ and is fire resistant then it won’t always have a positive influence on the service life. However, it will run cool which could help with its lifespan as there will be less temperature related lubrication issues.
Keeping a high level of oil cleanliness will also work well in extending the life of any hydraulic component.
Another point to ponder is how hard the pump is working. This is about how fast it’s spinning and under what pressure –how much of each hour is the pump under load? If they are under load for 55 minutes of every hour, then that’s going to be a 90% duty cycle, which is a lot to maintain compared to being under load for say 42 minutes of every hour. Under ideal conditions such as a duty cycle of 70% or less, 1200 rpm spinning with clean oil, you can hope an industrial grade hydraulic pump would last 20,000 hours or more. However, if you’ve got a 90% load with special purpose oil and 1800 rpm then you are more likely to get something in the arena of 10,000 hours of service life.
Running To Failure
There’s no doubt that these are only informed estimates using the information that we have about the pump and how it’s being used. Of course, if there are any hidden design flaws then the lifespan of the pump could be drastically compromised. For example, if there are pressure spikes that are caused by rapid valve shifts, then over time this could lead to a pump failure.
To continue to run a hydraulic pump until it fails is not a good idea. Its failure could cause consequential damage to other components. The cost of the rebuild of the pump will increase. Changing a pump before its life expires should be managed, whilst historical data is collected.
So if it’s looking like 20,000 hours is a strong lifespan possibility for any pump, then it’s wise to pull it out at 12,000 hours. It can be inspected and put back into service until say 15,000 hours. Then run to 17,500 hours and if all is well, then run until 20,000 hours. Getting too greedy will put the pump into the correct timeframe for a failure, so it’s not wise to push it too far.
Using this approach can provide information to make informed decisions on realistic expectations for component lifespan without putting the hydraulic system at great risk.
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.
It’s no secret that the use of hydraulic system filters is what makes all the difference when it comes to the expected longevity of your industrial machinery.
Keeping this in mind, it would make no sense to position your hydraulic system filters in a place where they could even produce results that reduce your machine’s life in service. That’s why it’s essential that you know where filters should be positioned so that you can avoid negatively impacting the system. Taking preventative action is far more favourable than addressing the resulting ailments.
With this at the forefront of our plans, let’s look at what you need to know about the range of potential suitable locations for your hydraulic filters:
Filters that are located in pressure lines deliver the ultimate in protection for fittings that are immediately downstream. It’s possible to use the pressure flow to your advantage and add filters with ratings of around 2 μm or less. If you have high flow velocities, you may experience a decrease in the effectiveness of the filter as there will be disturbance to any particles that are trapped. Pressure filtration usually proves to be the most expensive when it comes to installation and maintenance due to the need of them being high quality to withstand the pressure.
The philosophy behind using the return line for filtration addition is this: if both the reservoir and it’s fluid are clean, and anything that enters the reservoir has been filtered then it will continue to be clean. Fortunately the return line makes it possible to force fluid through fine filters such as those of 10 μm, but the pressure is not very high so will not interfere with design of the filter or housing and will make for an economical process.
Adding filters off-line clearly has both advantages and disadvantages, the latter being that it can have a high cost for installation. What it has going for it is that multi-pass filtration at controlled velocity flow delivers greater efficiency.
It’s no surprise that a filter located at the pump intake is in a great position. It becomes more efficient due to not having high fluid velocity nor high pressure. However, these benefits can be offset by adding a restriction to the intake line and what it can do to pump life.
Both cavitation and mechanical damage can result from having a pump inlet restriction. The fluid can be contaminated by cavitation and it may damage critical surfaces, with destruction occurring from vacuum induced forces on the pump.
The detriments of vacuum
In an axial-piston type pump, there is an issue with having a vacuum in the pumping chambers. It puts the piston ball and the slipper pad socket under tension that they’re not designed for and the slipper may even become detached from the piston. This can happen over time or even instantaneously.
The piston of the bent-axis pump usually fairs far better when it comes to withstanding a vacuum. It’s typically more indefatigable and a bolted retaining plate holds the piston ball in place in most cases. However, there can still be issues with the piston stem under high vacuum.
When it comes to vane pumps, it’s essential for the vanes to extend from their position of retraction in the rotor during inlet. If there is high vacuum at the inlet of the pump, then it will act on the base of the vanes. They may lose contact with the cam ring, and then get bashed around as the pressurized fluid enters. This can result in catastrophic failure.
In some cases, engineers regret trying to save their hydraulic system from suffering from fatigue and damage and rue the day they made changes. The best hydraulic systems have been designed to take filtration into consideration so that extensive changes don’t need to be made, and cavitation and mechanical damage are kept to a minimum.
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