Making Sense of Hydraulic Hose Standards

ISO 18752 classifies hoses according to their resistance to impulse into four grades: A, B, C, and D. Each grade is classified by outside diameter into standard types (AS, BS, and CS) and compact types (AC, BC, CC, and DC).

Note that ISO 18752:2014 does not include requirements for end connections. It is limited to the performance of hoses and hose assemblies. The hose assembly maximum working pressure is governed by the lowest maximum working pressure of the components.

Testing for Toughness

The primary concept behind ISO Standard 18752 requires constant-pressure performance ratings in each class for different hose sizes. This specification also requires spiral hose to exceed one million pressure impulse cycles according to ISO 18752 hose grade D, type DC. This requirement is the toughest of all grades and classes to achieve and specifies meeting 248°F temperature and an impulse pressure of 133% of maximum working pressure for at least one million impulse cycles. In this accelerated test, the hose is positioned into a U-shape on a test stand, and the fluid is raised to the specified working pressure. Pressure pulses are also applied at an elevated value to stress the spiral wires and end fittings for a minimum number of required cycles.

The ISO 18752 standard makes it easy to identify what hose should be used on a machine. Strict testing requirements allow users to know exactly what the hose is rated for and how it should perform while on hydraulic equipment. Hoses tested to higher impulse standards are likely to have a longer hose life, which is why many users are switching to ISO standards. For instance, if you need a hydraulic hose for a severe application presenting many repeated pressure cycles in short time and long continuous service, you would select either the grade C or D hose assemblies. However, this selection is based on the hose being correctly installed and protected from harsh environments.

Another important aspect of ISO standards is that they are accepted worldwide, which means wherever your hose is manufactured or purchased, you know it will be tested to the same standards. Global manufacturing standards are essential for many original equipment manufacturers.

A Step Ahead of Standards

In response to market trends for higher-pressure hoses, hose manufacturers have developed families of constant-pressure hoses that meet and exceed ISO 18752 specifications. For example, Parker’s GlobalCore line includes 1,000-, 3,000-, 4,000-, 5,000-, and 6,000-psi hoses. Each constant-working-pressure family has color-coded laylines based on pressure rating and is available with different covers to match application requirements. These hoses meet the minimum 1 million cycles required in ISO 18752 Grade D, Type DC and have been tested up to 2 million impulse cycles and at a tighter bend radius than required by the specification.

Although SAE J517 and ISO 18752 do not require pressure impulse testing while the hose is moving, Parker and other manufacturers do so to further ensure hose longevity. Hoses are flexed while impulse pressure cycles are applied randomly to positively demonstrate hose performance and longevity.

Hydraulic hoses meeting ISO 18752 are specified by the performance definitions below. These ISO definitions identify the grade and type of hose required for different applications based on criteria such as temperature, impulse pressure or cycle ratings.

This material is excepted from material by Kyri McDonough, marketing services manager, and Derek Garceau, engineering manager, both at Parker Hannifin’s Hose Products Div., Wickliffe, Ohio. The original material appears on Parker’s Motion & Technology Blogs. Click here to view the original material.