Hey Rich! There is a few reasons that could cause a pulse hose to rupture. From my own personal experience, if you use your pressure washer outside a lot and it's getting baked in the sun all day the hose becomes brittle over time and ruptures.
There are other variables as well. Debris in one of the cylinders or a malfunctioning unloader valve could cause an unwanted spike in pressure resulting in a rupture in your pulse hose. The part number you are after is A16746. It is figure 120 on page 2 on the breakdowns.
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