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

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Abschnitt 5.1, 5 Working on machines and systems 5.1 General
Abschnitt 5.1
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 5.1 – 5 Working on machines and systems
5.1 General

Basically, the manufacturer's provisions in the operating instructions have to be observed.

Along with the basic general safety instructions for maintenance work and for handling hydraulic components (see section 4), the following section contains further notices for the safe hydraulic maintenance on stationary machines and systems (see figure 24).

5.1.1
Reducing hydraulic energy

Before starting to work, the hydraulic energy in the system has to be reduced. Re-closing of the system has to be prevented. If individual hydraulic circuits of the hydraulic system are separated from the common pressure supply, it has to be checked if the correct connection has been disconnected.

Furthermore, the accumulators connected to the hydraulic system have to be disconnected from the system or depressurized (see figure 25). The depressurization must not lead to new hazards, e. g. loosening of clamping devices. The complete pressure reduction has to be checked (see "five-finger rule" in section 1.5).

Fig. 25 Depressurized hydraulic accumulators with closed pressure lines

Despite the energy supply being switched off, hydraulically elevated loads, e. g. machine parts, work platforms, hydraulic vertical axes, cause a substantial pressure in parts of the hydraulic system. On more complex machines and systems, this pressure can transfer to further parts of the system. Thus, elevated loads, e. g. material to be conveyed or machine parts, have to be lowered, secured using existing locks, or supported in a safe manner before starting the maintenance work.

After reduction of all pressures supplied into the hydraulic system, it is possible that residual pressures still exist in trapped heads of fluid between valves and other parts. These have to be reduced as well, e. g. by operating the valves several times or in accordance with the manufacturer's provisions.

The opening of the screwed connections on hydraulic lines should proceed at first slowly and carefully after the depressurization took place. The further loosening of the screwed connections should be done carefully as well, in order to realize possible hazards caused by the still existing pressure of the hydraulic fluid in time (slightly knocking on the screwed connection is helpful) and to take protective measures. If pressure is still present, the screwed connection must not be loosened further. The depressurization in the system has to be repeated and the effects of this procedure have to be re-checked.

5.1.2
Re-commissioning

Upon completion of troubleshooting and correction of faults the connections and parts have to be checked for compliance with the specifications of the circuit diagram. All loosened screws, line connections (see figure 26), and electric plug-andsocket connections have to be tightened and checked.

After completion of maintenance work, it must be observed that tank lines be reopened, if they were closed before.

The following measures have to be taken to prevent hazards caused by possibly occurring machine malfunctions after completion of the repair work:

  • protective guards have to be brought to their protective position or activated,

  • protection by means of distance.

Fig. 26 Markings on pipe and hose side

After completion of the maintenance or repair work on the hydraulic parts these have to be filled and vented. The running-in and adjusting specifications have to be observed for the pumps in particular. Hydraulic pumps mostly are self-priming.

Adjustment work on the pressure relief valves must only be conducted by the manufacturer or in accordance with the manufacturer's specifications, e. g. according to the pressure measurement sheets. It is imperative to adhere to the sequence of the procedure contained therein.

Incomplete venting procedures may lead to failures and hazards in machines and systems caused by suddenly starting movements. Venting the system completely prevents unforeseeable sudden movements of hydraulic cylinders and motors, e. g. stick slip.

After bleeding of the hydraulic system, all hydraulic functions have to be checked. In doing so, the specifications regarding safety have to be observed, e. g. reduced system pressure, screenings. When testing the hydraulic functions, it is important to keep sufficient distance as regards to reaching danger areas. It has to be ensured that neither the maintenance technician nor other persons stay below elevated loads or in danger areas.

All functions of cylinders have to be tested separately, if possible, at reduced speed and without loads.

Supports and safety measures for elevated loads must be removed only when the load is held safely by the hydraulic system again.