Hyundai HL955 Manual page 516

9) Disassemble and/or assemble the hydraulic equipment only in a clean place free of dust. When
disassembling, be careful about the interchangeability of parts, and clean the disassembled parts
with pure and clean mineral cleansing oil. Clean the internal passages as well. After the parts
have dried, wipe them off with a clean lint-free cloth.
10) When overhauling the hydraulic equipment replace all O-rings, backup rings, etc. with new ones.
Assemble O-rings with grease or vaseline applied.
11) After installing the equipment, add more hydraulic oil to make up for that lost during disassembly.
12) Tighten joints correctly. Loose joints will cause the hydraulic oil to leak. If the oil leaks, the tank oil
level drops and air gets sucked in, so the pump will break down. Also loose joints in suction lines
will take air in and might cause abnormal noise, malfunction or damage to pumps.
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