bike pump hose split
If its at a point where the hose bends naturally, then it could be weakened by flexing.  

What about temperature?  Could it be the hose is simply perishing with age?  Heat accelerates aging, so if its been hot or in sunlight for a while it will age quicker.

Look very closely at the split.  Is it smooth or slightly rough?  If its smooth, consider a sharp object may be involved.   Or is the hose getting caught under a weight, or in a door or track?

Do you have cats or kids ?  One has claws and the other can have scissors. 

Answer: Time for a new length of pressure hose with the right Internal Diameter.  Outer diameter is less important, and matters only at the ends..  inside  Get a couple metres and fit it.  You may need some small hose clamps too.    Do try and repair it, a good pump should last a hundred years.