The formulation of the Mining Design Guideline number 41 (MDG 41) came from an industry group set up by the New South Wales Department of Primary Industries in Australia and included global suppliers such as DBT, Joy, and suppliers of fluid power components. A key driver in the development of the committee and document was in response to an increasing number of incidents involving high-pressure fluid injection injuries at mining sites.

Companies that produce mining machinery in the US for the global market are now referring to MDG 41 as the latest and most up to date specification. MDG 41 covers the whole process from inception, design, product used, training, installation, etc., giving it recognition as the complete process in one place. But MDG 41 should not be viewed as a mining only specification. MDG 41 is useful for all fluid power applications and should be the benchmark across all industries where hydraulic hose and fittings product are used.

Specific problems addressed
The attachment of a fitting to the end of a hose is a complex engineering solution. International hose standards specify a set of materials and tolerances, such as internal and external dimensions, along with reinforcement types and dimensions. Although these standards are adhered to by all manufacturers, the tolerances themselves are so broad that if the entire tolerance allowance was used in manufacturing, hose assemblies would suffer a high failure rate due to tolerance mismatching. Therefore, manufacturers adopt their own limits that are often less than half of the allowed range.

This is where mixing and matching becomes an issue. Component manufacturer A could produce parts on the lower limits of the tolerance, whereas manufacturer B’s components fall at the upper limit of the tolerance. If an end fitting from B was put onto a hose from A at the specified crimp diameter of B, there would be little chance of adequate end fitting retention. Similarly, if a fitting from A was assembled onto a hose from B, the inner tube of the hose would likely be over compressed or the hose reinforcement could be cut. In either case, premature failure would result.

MDG 41 stipulates hose assemblies shall only be carried out using “Matched Hose and Fittings” (MDG 41 Clause 3.7.6.1k). MDG 41 Clause 1.6.13 defines a matched system as, “where the hose and fittings (insert/ferrule) are from the same manufacturer and are assembled and crimped using the method as specified by that manufacturer.”

This discussion was provided by Ryco Hydraulics Inc., Houston. For more information, visit www.ryco.com or call (281) 821-4100.