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The term 'primary crusher', by definition, might include any type and size of crushing machine. It implies that at least two stages of crushing are involved, but in many cases the machine which performs the function of initial crushing is the only crushing machine in the plant.

The factors influencing its selection and purchase for this service are much the same, regardless of how many crushing stages there are in the flow sheet; and therefore, this term, by common usage, is applied to the breaking equipment which takes up the job of reduction where the blasting operations leave off.

Selecting the right type and size of primary crusher is a problem of prime importance in the designing of a mining machinery of any nature and size. Usually this machine is the largest and most expensive single item of equipment in the plant; a mistake in the choice can only be remedied fully by replacement; and because the entire primary crushing equipment house arrangement is generally 'tailored' to fit the breaker, such replacement is almost always a costly procedure. While personal favoritism toward some particular types may safely be allowed to swing a close decision, it should never blind the engineer or operator to the merits of other types, nor to the limitations of his favorite.

The following factors all have a more or less important bearing upon the choice of the primary crusher.

1. The name, hardness, humidity of material

2. The hourly, daily or yearly capacity is required

3. The final product size or discharging size

4. Type and size of quarry equipment

5. Method of feeding.

The first three of these factors will almost always be ascertainable at least to a close approximation before the matter of jaw crusher choice is taken up. Sometimes, as when a new crushing plant-a new primary impact crusher is set up, it is to be installed at an existing operation the last three factors will be pre-established. Otherwise, it is sound practice to consider them as a part of the problem of Raymond mill selection. The primary crushing setup is closely linked to the quarrying or mining operation, and it is only by careful adjustment of all equipment selections to the general plan of operation that optimum operating results may be realized.

While it is convenient to discuss the influence of these several factors separately, it is well to keep in mind that they are more or less closely interlocked, and that a change in one of them may necessitate altering one or more of the others.

In addition to the factors listed there are usually a few which are peculiar to each individual problem such as labor costs and so on. Any plant design problem is an economic as well as an engineering one. We are concerned he re chiefly with the engineering phases.