Changing out a hydraulic gauge on an industrial wood chipper is a relatively simple process.
Locate top plate and carefully remove the nuts holding the plate to the tank.
Remove top plate and place into a clean bucket.
Locate the drain plug. Loosen and remove, drain the hydraulic fluid into a clean bucket to re-use. Have a helper watch the fluid level from the top and put the drain plug back in once fluid level is below the gauge.
Loosen bolts on the gauge and remove. Remove gasket and clean off the area.
Be mindful to use correct bolts for replacement gauge, it may come with different sizes.
Mount the new gauge and carefully countersink the bolts as you tighten them down.
Refill the hydraulic tank, replace top plate.
Then get back to work!