Contamination Control Contamination enters the fluid at many points. 8.2 Filling Methods Contamination can enter via dirty funnels or other unhygienic filling methods. Moog recommends a transfer pump either hand or electric operated, filling preferably via a quick disconnect coupling upstream of the 3 micron low pressure filter. Alternatively a 3 micron filter on the transfer pump is recommended. When in doubt remove the servovalve, fit a flushing block and flush the system out before refitting the valve.
Many factories have very dusty air in the vicinity of the hydraulic power unit.
Sometimes the dust is corrosive. In systems with large air flows in and out of the reservoir, presses with large cylinders for example, the example, the reservoir is drawing in particle laden air. Moog recommends a 3 micron breather. A fully sealed system or a breather line piped external to the factory atmosphere. 8.4 Airborne contaminents are also collected on the 'wet' rods of hydraulic cylinders and will be drawn into the cylinder in varying amounts, depending on rod wiper efficiency.