Fig. WH 117
(1) Breather filter with double check valve
Response pressure of outlet valve 0.35 bar (35 kPa)
Response pressure of inlet valve -0.03 bar (3 kPa)
(2) Check valves act as back pressure valves, opening pressure 2.5 bar (250 kPa)
(3) Integrated filter with bypass valve and paper element
(4) Sight glasses
The hydraulic oil reservoir is pressurized, i.e. the air above the oil level has an overpressure of 0.35 bar (35 kPa). This improves the intake characteristics of the hydraulic pump.
For oil quantity, type and change intervals see "Inspection and Maintenance Schedule" and "Table of Capacities" in the Operation and Maintenance Guide.
The breather filter, with double check valve, has the following purpose: the build-up of pressure in the reservoir. Air can only enter the tank through the inlet valve and leave through the outlet valve. This means that air exchange with the atmosphere can take place only when considerable level and temperature changes occur in the tank. Due to the different volumes of the piston side and rod side of the cylinders, the oil level in the tank drops when the cylinders are extended and air enters the tank through the inlet valve. When the cylinders are retracted, the level rises and the air above it is compressed until the outlet valve opens.
The entrance of dirt from the atmosphere is substantially reduced by limited air exchange. Splash and rain water must not enter the tank when the machine is not in use.
To a great extent, oil leakage through the breather filter as a result of oil movement is prevented. Change breather filter at regular intervals. (See Operation and Maintenance Guide.)
The check valves, which are integrated in the two return lines, bank up the returning oil. Thus, some of this oil flows back to the tank through the oil cooler and a further return line.
The integrated filters are in the return line directly on the tank. The filter outlet is below the oil level to avoid frothing (foaming). Two filter tubes with two filter elements each are fitted.
On the upper section of the filter tubes are the bypass valves, which open when the elements are badly soiled, so that unfiltered oil reaches the tank. Check the setting of the spacer screws before placing the cover over the filters. The spacer screws should cause the filter tubes to press against the O-rings slightly when the cover is fitted. Pour the oil through the hole in this cover so that it flows through the filter before reaching the tank. See Operation and Maintenance Guide for filter element change.
The sight glasses are for checking the oil level. Make sure the machine is level and lower the bucket to the ground. The oil level should reach to the middle of the upper sight glass.