Changing the filter element in your hydraulic machinery is a very important part of routine maintenance and for this reason it is often tacked onto a schedule and done at a set time, usually determined by the number of hours it has been in service for. Changing filter elements, wherever they are situated in the hydraulic loop, needs to be done in order to keep the fluid as clean as possible to therefore prolong the life of the components in the system, however, getting the timing right to ensure you are making the most of your expensive filter elements is a more intricate art than simply totting up the service hours and basing a filter change schedule on that data alone.
If a filter element is changed early it will still have plenty of dirt holding capacity left, and to replace one with life left in it is a false economy – yes, you will not run the risk of leaving it too late and potentially allowing contaminants into the oil, but it is also a waste of resources. Leaving an element change too late means that dirt can enter the system and cause damage to the components, leading to machine failure and spiralling associated repair costs. If we cannot use service hours to inform the timing of a filter change, how can we tell when is the right time for a switch?
The location of the filter can make a difference to the regularity of the element changes, as pressure filtration systems work a lot harder than off line or return filter systems. They are often higher in initial cost as well as in ongoing maintenance costs, but offer a fine level of cleansing as they can trap the smallest particles, thanks to the pressure forcing the fluid through the filter. The same pressure can dislodge trapped dirt, sending it back into the machinery and causing damage, so there are also downsides to using this location for hydraulic fluid filtration. Off line filtration systems are also very expensive but are the most effective at filtering, as they run continuously and therefore offer the best extension of machinery life. They also require regular replacement of the filter elements, as they are active for much longer than a filter that is only operational while the machinery is running. Return filtration is the most popular and most economical location for filtering hydraulic fluid within a system and also offers the opportunity to filter new oil in via the same part of the loop.
The best way of knowing when a filter element needs to be changed is to monitor the pressure drop across the filter, with a marked drop in pressure on the downstream side indicating that the dirt holding capacity is almost used up. A clogging indicator is one way of measuring the pressure drop and this can be used when it is suspected that the time may be approaching. Clogging indicators can be visual or electronic and set to go off before the pressure for the filter bypass valve is reached. Not all hydraulic systems have a filter bypass, but those that do can link the associated pressure point to the point at which a clogging indicator is activated.
A more sophisticated system involves continually monitoring the pressure drop across the filter, wherever it is located, and the resulting data can be used to inform a more reasonable and reliable filter element change schedule, as it shows the true lifespan of the filter elements. The data also acts as an early warning system of system or component failure. Although an advance continuous monitoring system costs more, in the long run it will save money on unnecessary filter changes, warn of expensive system failure before it happens and provide valuable information about the operating capacity of your hydraulic equipment that could prove a lot more valuable in the long run, and just think – all these benefits can arise from simply trying to work out a proper filter element replacement schedule!