Short answer
A critical part is not an expensive part; it is one whose absence stops the machine and which cannot be obtained quickly. Three criteria define criticality: probability of failure, lead time, and whether you can work without it. Assessed together, the stock list usually comes out shorter than expected: a few lines on site, the rest at the supplier. The right stock list is determined from your own failure records, not from guesswork.
The three criteria that define criticality
- Failure probability: how often does this part fail? Wear parts (tools, seals, bushings) are high probability, body parts low.
- Lead time: how long does the part take to arrive? A part held in local stock may not need stocking even if critical; a part that has to be imported should be stocked even at low probability.
- Is it a stopper: can the machine work without this part? If not, criticality rises; if you can manage temporarily, it falls.
Typical critical lines
On a breaker the highest-probability group is wear parts: tools, seal kits, bushings and the retaining pin. These are consumed regularly and the machine stops when they run out.
The second group has medium probability but potentially long lead times: diaphragm, accumulator components, valve parts. Whether to stock these is decided by lead time.
The third group is body parts (piston, cylinder, front head). Because their probability is low they are usually not stocked, but if the fleet has many of the same model, holding one set can make sense.
Which part falls into which group in your working conditions is shown by your own failure record. Without records the list rests on guesswork and is usually either excessive or short.
Records write the stock list
A simple two-year failure record shows how many times each part was replaced and writes the stock list by itself. In businesses that keep no records, stock either swells "just in case" and ties up capital, or a critical line is missing and produces downtime. A four-column sheet solves both.
Compare stock cost with downtime cost
Holding stock has a cost: tied-up capital, storage space and, for parts with a shelf life such as rubber seals, the risk of deterioration.
The decision comes from comparing that cost with the downtime the absence of the part would cause. If you know your downtime cost, the comparison is clear; if you do not, the decision stays at the level of a hunch.
Shelf life matters for rubber parts; over-stocking seal kits can leave them ageing unused. Cool, dark, dry storage reduces that risk.
Keeping stock manageable
- Label by model: which part belongs to which breaker should be readable on the shelf. In a fleet this is where confusion arises most.
- Use standardisation: models sharing the same parts reduce stock lines; make this a criterion when buying new equipment.
- Set minimum levels: order when a line drops below that level; a "buy it when it runs out" approach produces downtime.
- Record parts used: if every part leaving stock is also entered in the failure log, the two records feed each other.
- Clarify lead times with your supplier: knowing how long each part takes is the foundation of the stock list.