4 OPERATION No D. 02 : Work on the hydraulic system 3. PRECAUTIONS AFTER DISCONNECTING THE UNIONS. Close the open ends of all pipes For the metal pipes use screwed unions, For pipe assemblies protect the union flanges with self-adhesive masking-tape. Protect plastic pipes in the same way. For rubber pipes use cylindrical plugs : diameter = 8mm length = 50 mm diameter = 12 mm length = 50 mm 4. PROTECTION OF HYDRAULIC UNITS AFTER REMOVAL : Seal all the openings in the units as dismantling proceeds, IMPORTANT NOTE : All the plugs must be carefully cleaned before use, 5. PRECAUTIONS BEFORE ASSEMBLY.