From a predictive maintenance perspective, there is little real benefit from taking an oil sample directly from the hydraulic tank. Sure, an oil sample taken from the tank can be used to establish the cleanliness of the fluid, and the condition of its base oil and additives.

But these days, most hydraulic systems feature a return filter, and so sampling from the tank–and therefore after the return filter, eliminates the predictive intelligence that can be gathered by sampling just before the return filter. Fluid taken immediately upstream of the return filter can still be used to establish the cleanliness level of the fluid, and the condition of its base oil and additives, PLUS it can also provide valuable insight to the condition of the components in the system.… continue reading »

When it comes to sizing a hydraulic reservoir, my motto and advice is the bigger the better. Because the greater the tank volume the longer the dwell time the oil has to give up contaminants – particles, water and particularly air. Size DOES matter.

The rules of thumb for reservoir size – and that’s all they are – differ for open and closed circuits. For open circuits the general rule is a tank oil capacity of 3 to 5 times the flow of the pump(s) per minute plus a 10 percent air cushion. For HFC and HFD fire-resistant fluids the general rule is 5 to 8 times pump flow per minute.… continue reading »

In AC electric coils the resistance or impedance of the coil is lowest when the solenoid is open, i.e. when the plunger is out. Impedance increases as the plunger is pulled into the closed position. As a result, the current draw of an AC solenoid is highest when the solenoid is open (plunger out) and lowest when the solenoid is closed (plunger in).

The high current draw of an open AC solenoid is known as inrush current. And the current draw when the solenoid is closed is called holding current. AC solenoids can only dissipate the heat generated by their holding current.… continue reading »