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

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Abschnitt 1.3, 1.3 Hazards when working on hydraulic systems
Abschnitt 1.3
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 1.3 – 1.3 Hazards when working on hydraulic systems

A hazard analysis has to be conducted for maintenance work and documented together with the resulting protective measures (see also TRBS 1112, section 4, paragraph [2]). The risk assessment for the maintenance technician must be conducted by the head of the maintenance department.

For recurring, identical maintenance work (e. g. replacement of hose assemblies, valves or cylinders), it may be sufficient to carry out risk assessments once and use this as a basis for operating instructions and regular instruction.


In case of particular hazards (e. g. due to reciprocal effects with other work or at new, unknown places of operation or in the premises of customers), a risk assessment must also be conducted before maintenance work is started and, if necessary, it may have to be coordinated with the responsible safety and health coordinator of the customer.

Working on hydraulic systems can lead to the following hazards:

  • uncontrolled leakage of the hydraulic fluid,

  • accidental machine movements,

  • risk of burning at hot surfaces or hot hydraulic fluid,

  • parts coming off or bursting,

  • skin diseases,

  • noise.

Uncontrolled leakage of the hydraulic fluid

The leakage of hydraulic fluid has to be expected if lines rupture, if connection elements that are still pressurized become loosened, if hydraulic hose assemblies (see figure 2) are damaged, or if inadmissibly high forces are applied. The consequences can be:

  • damage to the eyes,

  • intrusion into the skin (intoxication),

  • scalding by hot hydraulic fluid,

  • risk of fire, if there are ignition sources (e. g. oils on hot surfaces),

  • slipping danger on work stations and traffic paths,

  • hazards due to accidental machine movements,

  • environmental hazards, (e. g. intrusion into or release to the ground/ groundwater).

Inadmissibly high forces can occur due to

  • improperly set pressure valves,

  • modifications, e. g. on pressure relief valves,

  • improperly rated valves (switching too fast),

  • loads applied externally,

  • accidental pressure intensifications on cylinders.

Accidental machine movements can be triggered by

  • accidental operation of command or control devices, such as buttons, levers, controlling light barriers, proximity switches, manual overrides, as well as interferences by magnetic fields,

  • errors in the control system,

  • energy separation, energy supply, residual energy,

  • parts failure,

  • contamination of the hydraulic fluid.


Fig. 2
Bursted hydraulic hose assembly

Residual energy in a system can be present if

  • accumulators (hydraulic/pneumatic) exist in the system,

  • loads are maintained in elevated positions,

  • clamping forces exist,

  • there are tensions between parts.

Parts failure can result from e. g.

  • excessive system pressure,

  • wear and tear and material fatigue (e. g. valve springs),

  • stuck valves,

  • overload due to excessive dynamic pressure peaks,

  • improper or contaminated hydraulic fluids.

Risk of burning on hot surfaces and hot hydraulic fluids by:

  • machine parts that are hot during operation, such as line assemblies, pumps, motors and

  • escaping hydraulic fluid, e. g. when lines are opened or components are removed.

Parts coming off or bursting can be the result of

  • overloaded components, e. g. due to excessive operating pressures or pressure peaks,

  • material fatigue,

  • parts selected improperly.

This also comprises whipping hydraulic hose assemblies ruptured on one end.

Contact with hydraulic fluids can lead to effects hazardous to skin (see section 2). Vapors of hydraulic fluids can cause airway irritations when inhaled.

Noise emissions are not only caused by the pump unit, even the noise of machines generated during operation can cause a substantial level of noise, e. g. during troubleshooting, test operation and others. Thus, the maintenance technician of the hydraulic system has to wear ear protection in case of noise emissions hazardous to health.

Depending on the maintenance work, one or more hazards can occur simultaneously. Thus, several protective measures have to be used. The most important protective measures are explained in the individual sections of this information brochure. If required, references are made to other DGUV information brochures.


Should the risk assessment of maintenance work identify explosion hazards, the Technical Rule for Operating Safety (TRGS) 1112 Part 1 "Explosionsgefährdungen bei und durch Instandhaltungsarbeiten - Beurteilungen und Schutzmaßnahmen" (Explosion risk arising during and due to maintenance work - assessment and protective measures) must be applied.