Preventive maintenance is a must for hydraulic systems, and the range in which it is taken seriously is vast. Some machines are old as dirt, with original filters, but somehow still run. Other machines can be meticulously looked after, but still have inexplicable failures, such as a worn out pump.
Hydraulic pumps are robust, to be sure, but that doesn’t mean they’re immortal. Even the highest quality piston pump can only last so long when wear surfaces are metal-to-metal, such as they are. If your maintenance routine is stricter than a Marine Corp boot camp, the possibility for a failure during hot production periods is still there; pumps just wear out over time.
I like to recommend stepping up from preventive maintenance to predictive maintenance. It’s a topic I’ve covered before, but one tool of predictive maintenance that gives you command over random pump failures is monitoring of case drain flow. Pumps require some leakage flow to lubricate surfaces, such as the wear plate or piston-to-bore clearances. In a piston pump, for example, you might normally see ten percent of rated pump flow used as leakage.
A 10 GPM piston pump might normally see 1 GPM constant drain flow, which normally dibbles its way back to tank with no restriction. By measuring case drain flow, we can monitor and log the wear rate of the pump. A simple low-backpressure inline flow meter will do the trick. Once the meter is installed, you take a baseline reading and then take regular readings to be logged in a spreadsheet to track pump wear.
You could see case drain flow stay at around 1 GPM for years, and then it could creep up to 1.5 and then 2 GPM over the course of a week. This sudden increase in case drain flow is a signal of pump wear, even if the machine is still operating well at the moment. You may want to aside time to change the pump during production downtime or tool changes. Production can then start up again as scheduled, and your boss will throw you a parade complete with ticker tape and cartoon character balloons!