Identifying the hydraulic pipes / hoses.
- The flow and return pipes are usually the two biggest. They can be rubber hoses or steel pipes and are a matching pair.
- Case drain. If there are only three pipes the smaller of the three will almost certainly be the case drain. If there are four or more pipes the case drain is likely to be bigger than all but the flow and return. It is a low pressure pipe and is sometimes attached to the travel motor with a ferrule and jubilee clip. Whilst disconnected oil will continually flow at low pressure from the pipe while the engine is running.—IT IS VERY IMPORTANT TO LOCATE AND CONNECT THIS PIPE CORRECTLY.
- Two speed. This tends to be the smallest pipe of all. Oil will not flow from this pipe unless the machine is in high speed mode.
- Brake port. If fitted this pipe will be small and will pressurise only when the travel lever is operated.
- 3 Ton mini excavator final drive with integrated 2 speed travel motor showing 4 front entry ports
- 6 Ton midi excavator final drive with integrated 2 speed travel motor showing 4 entry ports. Note the somewhat unusual position of the case drain port.
- 12 Ton excavator final drive with “plug in” 2 speed travel motor and separate brake port in the gearbox.
- 13 Ton excavator final drive with integrated 2 speed travel motor showing 4 front entry ports.
ATTENTION Case drain — Leak-off. All piston type hydraulic motors leak oil from the barrel and piston assembly (sometimes called the rotating group assembly) into the motor casing. This leakage is deliberate and lubricates the piston slippers and swash plate (or thrust plate) as well as the interface between the valve plate (or lens plate) and the cylinder block. The oil that leaks into the motor casing has to find it’s way back to the tank under very little pressure and a leak-off pipe (or drain line) runs from the travel motor to the hydraulic tank for that purpose. If the leak-off pipe is not connected or becomes blocked or pressurised, oil pressure will build up in the motor casing and can, and usually does, cause catastrophic damage to the travel motor and often the final drive gearbox. It is therefore vital to ensure that the leak-off pipe is connected correctly, is not obstructed and has no significant back pressure.