Given that the primary aim of filtration in hydraulic systems is to remove contaminants from the oil and thus extend the life of hydraulic components, it presents a contradiction when filters are positioned in a way that actually reduces the lifespan of the very components they are meant to safeguard.
When contemplating the placement of filters within a Car Lift Repair Tampa Florida hydraulic system, the guiding principle should be to avoid causing harm. This means ensuring that the solution to the contamination issue doesn’t create further problems. With this principle in mind, let’s examine the advantages and disadvantages of different locations for hydraulic filters:
Pressure Filtration – Placing filtering media in the pressure line offers maximum protection for components downstream. It allows for filtration rates as fine as two microns due to the pressure pushing fluid through the media. However, high flow velocities and pressure and flow transients can diminish filter efficiency. The main drawback of pressure filtration lies in its economic impact. The design of housings and elements to withstand peak system pressure results in higher initial and ongoing costs.
Return Filtration – The rationale behind locating filtering media in the return line is to maintain Car Lift Repair Tampa Florida oil cleanliness by ensuring that the tank and its contents remain clean and that incoming air and returning oil are adequately filtered. Another advantage is that the return line allows for sufficient pressure to force fluid through fine media (typically 10 microns) without complicating filter or housing design. This, combined with relatively low flow velocity, enables high filtering efficiency at an economical cost. Hence, return filtration is a common feature in most hydraulic systems. However, the main disadvantage is the back pressure created by the element, which can negatively impact the operation of some components.
Off-Line Filtration – Off-line filtration allows for continuous, multi-pass filtration at controlled flow velocity and pressure drop, resulting in high filtering efficiency. It can achieve filtration rates as fine as two microns, and additional components like polymeric filters and heat exchangers can be incorporated for comprehensive fluid conditioning. The primary downside of off-line filtration is its higher initial cost, although this can often be justified over the Car Lift Repair Tampa Florida machine’s lifespan.
Inlet (Suction) Filtration – From a filtration standpoint, the pump intake serves as an ideal location for filtering media. The absence of high fluid velocity and pressure drop across the element enhances filter efficiency. However, the advantage of cleaner oil is offset by the restriction the element imposes on the intake line, potentially damaging pump life.
A restriction at the Car Lift Repair Tampa Florida pump inlet can lead to cavitation erosion and mechanical damage. Vacuum-induced forces from cavitation can cause detachment of the slipper from the piston, leading to rapid failure. In bent axis pump designs, although the piston is more robust, high vacuum conditions can still result in tensile failure or buckling of the retaining plate. Vane pump designs are also susceptible to vacuum-induced damage, with excessive vacuum causing vanes to lose contact with the cam ring, leading to catastrophic failure. Despite being the least vulnerable mechanically, research shows that gear pumps can still experience a significant reduction in service life due to intake restrictions.
Over a decade of advocacy against their use, arguments for suction strainers usually revolve around issues of design or maintenance. Claims that suction strainers are necessary to protect pumps from debris resulting from poor maintenance practices are refuted by the fact that properly designed reservoirs with pump intakes positioned four inches above the tank bottom minimize such risks. Similarly, arguments for preventing cross contamination in systems with multiple pumps sharing a common inlet manifold are invalidated by proper design principles, where the manifold is positioned below the Car Lift Repair Tampa Florida pumps’ intakes, preventing debris from traveling uphill against gravity and a positive head of oil.
In my previous Car Lift Repair Tampa Florida blog post, I shared an image of a cracked piston pump housing. A comment from one of my Facebook friends suggested that such damage would only occur if the pump’s rotating group failed dramatically. However, based on my extensive experience in hydraulic repair, such a scenario is actually quite rare.
More commonly, cracked pump or motor housings result from a restricted or blocked case-drain line. Forgetting to connect the drain line essentially turns the housing into a pressure vessel, leading to a sudden failure.
Similarly, connecting a flowmeter to measure internal leakage without opening the loading valve can also cause catastrophic failure shortly after startup. Surprisingly, such incidents have indeed occurred.
Another frequent cause of cracked housings is the presence of filters in the drain line. If there’s a sudden surge of leakage into the case and it’s unable to escape due to filter restrictions, the resulting pressure spike can crack the housing or blow out its seal. Even without such dramatic effects, filters in piston pump or motor case-drain lines often lead to excessive case pressure, resulting in seal failure and mechanical damage.
Seal failure occurs due to the excessive load on the shaft seal lip, wearing a groove in the shaft and leading to leakage. If the case pressure exceeds the seal’s design limits, complete failure may ensue, causing oil loss and subsequent damage due to inadequate lubrication.
High case pressure also affects Car Lift Repair Tampa Florida axial piston pumps similarly to excessive vacuum at the pump inlet, putting the piston-ball and slipper-pad socket in tension during inlet, potentially causing buckling of the retaining plate or separation of the slipper from the piston, resulting in catastrophic failure.
In radial piston motors, high case pressure can lift the pistons off the cam during operation, leading to destruction during the outlet cycle as the pistons are hammered back onto the cam during inlet.
Given these risks, it’s not advisable to use depth filters on case drain lines. While this may allow a small percentage of fluid to return unfiltered to the reservoir, in most applications, the contamination risk is low and can be effectively managed through oil analysis and other condition-based maintenance practices.