Hydraulic filters that do more harm than good - Part 2
In response to my previous article on hydraulic filters and the negative effects of suction strainers, one of our readers wrote the following:
"The one thing a suction strainer does that's worthwhile is to keep out the trash that gets dropped into the tank during service. We lost pumps to things like bolts that we know were not in the tank when it got built. The process of adding hydraulic fluid to the tank often doubles as the trash-installation function. The screens that are often installed in the fill neck usually get a hole poked through them so that oil will go in faster..."
A couple of years ago, I was involved in a case where the seals failed in the swivel on a hydraulic excavator. This allowed the automatic greasing system to pump grease into the hydraulic reservoir.
The grease clogged the suction strainers, which subsequently failed. The wire mesh from the suction strainers destroyed all four hydraulic pumps and several other components.
Had suction strainers not been fitted, it is likely that the grease would have eventually dissolved in the hydraulic fluid with minimal damage to any components.
My point is, I don't use this example as an argument against fitting suction strainers - because grease should not be in the reservoir.
Likewise, I do not consider trash exclusion to be a valid argument for fitting suction strainers - because nuts, bolts or similar debris should not be in the reservoir.
The sloppy operators that allow trash to drop into the reservoir are the same operators that never drain and clean the reservoir, and change the suction strainer. So the suction strainer clogs eventually and the pump fails through cavitation. Therefore, with or without the suction strainer, the pump is destined to fail prematurely.
The correct solution is not to allow trash to get into the reservoir. And this is fundamental to my recommendation to remove and discard suction strainers, where fitted.
Excessive vacuum at the pump inlet caused by suction strainers is a bigger threat to pump life in the long run, than trash that shouldn't be in the reservoir in the first place.
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