We have drained the hydraulic fluid out of several sections of the hydraulic system when replacing hoses and swivel joint seals. Is there a proper way to replace this fluid? Will simply adding fluid to the reservoir and starting the engine cause damage to the pump? Thank you.
If you didn't take apart the pump, it should be fine. You want to avoid dieseling the air in the cylinder, so work any functions you opened at idle, and low speed back and forth a few times with as little force as possible to flush the air out. If you have a cylinder full of air, it can ignite from the compression heat, there will always be enough oil, and the pressure will be much higher than an engine compression.
Leave the hydraulic tank cap loose as you work the functions. That tends to let the air out of the system easier. Check the level and add oil as you run things. After a few cycles, top off the tank, put the cap on all the way and function all the implement function to full stroke. Go back to work.
Thank you everyone for the information. All this makes sense since the main pump is supplied from the hydraulic fluid tank just next to it.