In brief
An alternative part is a component from another manufacturer or of another type that can replace an original part equivalently in form, fit and function.
Contents
What is Alternative part?
Alternative parts, also called equivalent parts, are used when the original part has been discontinued, is difficult to obtain or is disproportionately expensive. The benchmark is the form, fit, function principle: the replacement part must have the same dimensions, be installable without modifications and perform the same function under the same operating conditions.
Suitability is checked technically, usually using data sheets, drawings and material specifications. Items to compare include dimensions, connections, performance data, materials, temperature and pressure ranges and electrical characteristics. For safety-relevant parts, it must also be checked whether the replacement affects the conformity of the machine, for example the CE marking, an approval or an explosion protection rating.
For maintenance, proper approval is decisive. The alternative part is documented with the reason, test result and approval date and linked in master data and bills of materials. This keeps it traceable which part is installed where, and later purchases draw on the verified solution. It should also be recorded whether the alternative part is approved without restriction or only for certain machines.
In practice: maintenance and procurement
The most important basis for finding an alternative part is the manufacturer part number, nameplate details, data sheet and installation situation. Technical approval should be given before the first order, not only at installation.
Synonyms and abbreviations: equivalent part · substitute part · replacement type · form-fit-function replacement · cross-reference part
Frequently asked questions
What does form, fit, function mean?
The formula describes three conditions for an equivalent replacement. Form stands for dimensions and shape, fit for the fit and installation without changes to the surroundings, and function for the same performance under the same operating conditions. Only when all three are met is a part considered directly interchangeable.
May an alternative part be installed without consultation?
That depends on the application. For safety-relevant components or approved equipment, a replacement can affect conformity. A documented technical approval by the responsible department makes sense. If in doubt, it should be clarified whether the machine manufacturer or an inspection body needs to be involved.
What documents are needed to check an alternative part?
Helpful are the manufacturer part number of the original, data sheets for both parts, drawings or dimensions, material specifications and the operating conditions at the installation location. For electrical components, characteristics such as voltage, current and IP rating are added. The more complete the information, the more reliable the assessment.