Under operating conditions hydraulic hoses are subject both to pressure load by the hydraulic fluid and to changing flexing load. Dynamic pressure testing (impulse testing) is carried out in accordance with DIN EN ISO 6803 "Rubber or plastics hoses and hose assemblies - Hydraulic pressure impulse test without flexing". In actual fact, flexing is not prescribed by this standard, so that the test conditions do not meet the field requirements. This drawback is partly counterbalanced by applying the test method described in DIN EN 26802 "Rubber and plastics hoses and hose assemblies with wire reinforcements; hydraulic impulse test with flexing" which provides for an impulse test with flexing of the hose. The project, which was initiated by several institutions for statutory accident insurance and prevention, was aimed to determine and compare the safety behaviour of hoses under the test conditions of DIN EN 26802 on the one hand and of DIN EN 6803 on the other.
Flexible hoses and crimped fittings from different manufacturers and of various nominal sizes and pressure steps were investigated on an impulse test bench. As described in DIN EN ISO 6803 and DIN EN 26802, the impulse figures were determined and evaluated until destruction of the hoses. Use was made of the basic test results in national standardisation bodies.
Some high-quality hoses of pressure steps 2ST (two wire braid reinforcements) and 4SP (four wire reinforcements, spirally wound) of different manufacturers were found to surpass the requirements of DIN EN 26802 and of the corresponding hose standards. For pressure step 4SP no significant effect of the DIN EN 26802 test method on the impulse values could be determined. For pressure step 2ST this test method (with flexing) lead to a slightly increased number of hose failures than were observed in the case of impulse testing according to DIN EN ISO 6803 (without flexing). The test pressure increase of approximately ten times the impulse pressure per second was included in the relevant standards. Hoses which are subject to flexing under operating conditions should be tested in accordance with DIN EN 26802. From the viewpoint of safety it is necessary to improve quality assurance in the production of flexible hoses.
-cross sectoral-Type of hazard:
Anlagensicherheit, Brand- und Explosionsschutz, MaschinensicherheitDescription, key words:
hydraulics, flexible hoses, pressure testing, impulse testing, hydrostatics