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Hydraulic System Filters: It’s All About Where ben lee

Hydraulic System Filters 

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:


Pressure filtration
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.


Return filtration
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.


Off-line filtration
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.


Suction filtration
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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