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| Illustration 1 | g02162045 |
Hydraulic tank (1) Return filters (2) Fill plug (3) Air breather (4) Boom and stick regeneration valve drain inlets (5) Case drain inlets (6) Return oil filter inlets (7) Suction filter (8) Suction line (9) Pilot manifold drain inlet | |
The return oil flows from the following components and into the hydraulic tank.
- Return filters
- Case drain filters
- Bypass check valve
- Boom and stick regeneration valves
- Pilot manifold
Three return filters are mounted on the rear surface of the hydraulic tank.
The oil passes through element of the return filter and flows into tank chamber. Thereafter, the oil passes through suction filter (7) and the oil is delivered to the pumps through suction line (8) .
Air breather (3) is mounted on the upper surface of the hydraulic tank. The air breather maintains a certain air pressure in the hydraulic tank regardless of the following circumstances :
- Change of air pressure in the hydraulic tank due to cylinder movement.
- Change of air pressure in the hydraulic tank capacity due to a temperature change.
Return Filter Bypass Operation
Normal Operation / Warm Oil
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| Illustration 2 | g02162046 |
(1) Return oil filter (2) Return oil (3) Spring (4) Bypass valve (5) Filter inlet manifold (6) Switch assembly (7) Port (line to tank) | |
The filter inlet manifold (5) contains a filter bypass valve (4) beneath the center return oil filter (1) . During normal operation when the oil is warm, return oil (2) from the hydraulic oil cooler and/or the cooler bypass valve and enters the filter inlet. The oil then flows upward through the center of the filter element. Contaminants are removed from the oil as the oil passes through the filter media. The oil is then returned through the filter outlet (7) to the hydraulic oil tank .
Filter Clogged / Cold Oil
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| Illustration 3 | g02162051 |
When the oil is cold or if the filter is clogged, the resistance to return oil (2) flow is high through the filter media. This resistance causes the inlet oil pressure to increase. When the pressure reaches approximately 150 kPa (22 psi), bypass valve (4) opens to the right against spring (3) . This action allows the oil to bypass the filter and flow directly into tank (7) .
A capsule filter switch assembly (6) is installed between the inlet and the outlet of the center return oil filter. The switch is mechanically connected to filter bypass valve (4) and is CLOSED in the normal position. When bypass valve (4) opens, the valve pushes the switch to the OPEN condition and the monitor will alert the operator that the hydraulic oil filters are PLUGGED.
When the oil is cold, the resistance to flow through the filter media is restricted, due to the high viscosity of the oil. The monitor will ignore the OPEN switch condition when the hydraulic oil temperature sensor in the tank indicates the oil is cold. When the oil warms, the viscosity of the oil is lower. Unless the filter is clogged, spring (3) will close bypass valve (4) allowing the oil to be filtered.