DGUV Information 209-071e - Safe maintenance of hydraulic systems (DGUV Informat...

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Abschnitt 6.1, 6.1 General
Abschnitt 6.1
Safe maintenance of hydraulic systems (DGUV Information 209-071)
Titel: Safe maintenance of hydraulic systems (DGUV Information 209-071)
Normgeber: Bund
Amtliche Abkürzung: DGUV Information 209-071
Gliederungs-Nr.: [keine Angabe]
Normtyp: Satzung

Abschnitt 6.1 – 6.1 General

In addition to the notices described already for the hydraulic system of stationary machines (see section 5.1) further aspects have to be taken into consideration for mobile hydraulic work equipment. Maintenance work is often conducted outside workshops, e. g. for self-propelled machines used on construction sites or off roads. In doing so, tools and aids are often available to a limited extent only.

Different operating pressure levels have to be observed for implementing maintenance work. Starting with approximately 60 bar for low pressure hydraulic systems for farm and harvesting machines, they range up to pressures of over 400 bar for earth-moving machines.

6.1.1 Securing the vehicle

In principle, vehicles should be positioned on firm ground when conducting maintenance work. This especially holds true for maintenance work on vehicles that can tilt or swivel attachments or superstructures, e. g. booms, hydraulically tiltable cabs, conveyor belts.

Before starting to work on the hydraulic system, the vehicles have to be secured against:

  • rolling due to uneven ground,

  • rolling due to force effect caused by the maintenance work,

  • tilting caused by changes to the position of the center of gravity (also when working with hoisting platforms).

Elevated parts or superstructures of vehicles have to be lowered to the ground, e. g. loading device, boom, or the required mechanical locks such as locking pins, cylinder support, and the like have to be used. Furthermore, all required locks have to be put in place, e. g. articulated steering lock for vehicles with articulated steering (see figure 30).

The support areas for possibly extracted supports have to be able to accept the forces present.


Fig. 30
Installed articulated steering lock

For drive-on platforms the wheels have to be secured by means of stop-blocks. When positioning the vehicles on column lifts with small centered platform the vehicle has to be lashed to the platform or wired (see figure 35).

string Note
Vehicles must not be accessed in lifted condition.

6.1.2 Depressurizing

Before starting any work the following has to be conducted:

  • mobile hydraulic systems have to be depressurized,

  • vehicle drives have to be switched off,

  • hydraulic systems have to be switched off,

  • hydraulic accumulators have to be closed on the pressure side and depressurized.


Caution with residual pressures caused by trapped fluid volumes, e. g. between valves and cylinders. They have to be depressurized by operating the control lever or the valve. The depressurization has to be checked, e. g. by means of a pressure gauge.

6.1.3 Collection container

When disassembling hydraulic components, drip pans of suitable shape and size (see figure 31) have to be positioned below the corresponding parts in order to collect possible leaking quantities of residual oil.


Fig. 31
Oil collection pan

6.1.4 Hose assemblies

Connections and attachments have to be loosened in accordance with the specifications of the manufacturer (see sections 4.2 and 4.3). If there is the danger of confusing the connections of the lines in the confined space of the vehicle (see figure 32), they have to be marked before being loosened or removed.

Before replacing hose assemblies, the depressurization of the mobile hydraulic system has to be checked in any case.

Damaged hose assemblies have to be removed wearing protective gloves as projecting metal wires from the meshwork pose a risk of injury.

Frequently changed attachments such as adjustment devices of the forks or swiveling devices mostly are equipped with quick couplers sealing both connection parts (attachment and line side) automatically after the line has been interrupted. When changing over to quick couplers, the specifications of the manufacturer have to be observed.


Fig. 32
Hose assemblies on a mobile hydraulic system

6.1.5 Disassembling heavy parts

Substantial forces can be present on the lifting cylinders of the vehicle superstructures. Before working on cylinders, these forces have to be accepted, e. g. by lowering the attachments or superstructures. If mechanical blocking by means of a bolt locking mechanism is not provided, the use of support frames is recommended (see figure 33).

Numerous hydraulic components, e. g. traction drives, main pumps, boom cylinders, are characterized by high dead loads and off-center position of the center of gravity. Thus, replacing these components has to be conducted with the help of lifting gear attached to the designed attachment points.


Fig. 33
Support frame when working on wheel-type loaders

6.1.6 Replacing the hydraulic fluid

Mobile suction devices used to empty the tank are suitable for replacing the hydraulic fluid (see figure 34). Replaced filters can drain with the help of a hopper device.

Mobile filling devices with integrated leakage protection/collection pan are particularly suitable for filling the system with new hydraulic oil.

When changing the hydraulic fluid, care must be taken that no contamination enters the tank or other parts of the hydraulic circuit. To achieve the desired cleanliness class, also freshly supplied hydraulic fluid must be filtered.


Fig. 34
Aid to dispose of old hydraulic oil

6.1.7 Fire hazards

Hydraulic fluid may ignite at hot surfaces, e. g. exhaust manifold, turbochargers. Insulating materials have a wicking function when contaminated with hydraulic fluid, which makes them easily inflammable.

Measures for reducing the fire hazard are:

  • removing leaked hydraulic fluid completely (see section 2.2) and wiping parts dry,

  • renewing soaked insulation material, e. g. noise protection lining,

  • avoiding external ignition sources, e. g. cigarettes,

  • covering hot surfaces.

6.1.8 Working while drive is running

Basically, repair work must only be carried out with the drive standing still. If work can only be conducted with the drive running, e. g. for testing and adjustment work, hazards have to be taken into account caused by:

  • unprotected mechanical drives with rotating parts,

  • hot surfaces of parts,

  • noise.

The work must only be conducted by trained and experienced maintenance technicians. When conducting these works corresponding technical and personal protective measures have to be taken, e. g. safety by means of distance, covers, hearing protection, and further personal protective equipment, if required.

6.1.9 Re-commissioning

After completion of the maintenance work, including the ready-to-operate filling and venting of the hydraulic system, the drive and work functions have to be tested individually and if possible at low speeds and load-free. This should be carried out either behind screenings or from the safe distance.

The following procedure is recommended for testing the functionality of the hydraulic system:

  1. 1.

    checking all valve functions for correct sense of direction and shutdown function (neutral position),

  2. 2.

    executing larger travels of cylinders or swiveling areas of motors.

While testing the functionality of the hydraulic system, the machine operator has to ensure that no persons stay in the danger area.

For further notices, see section 5.1.2.

6.1.10 Spare parts

Specifications or approvals of the manufacturer have to be complied with, e. g. regarding spare parts for hydraulic systems, hose assemblies, material specifications, hydraulic fluids, and the like.

string Note
The operating instructions (including maintenance and repair instructions), as well as the spare parts list have to be carried along or kept at hand on site in order to implement maintenance work on mobile hydraulic systems!