Hi,
There's a pressure switch in there that controls the pump via a relay.
If I remember correctly this is independent of the rest of the system, as in you can remove the abs ECU and the pump still works.
If the pump runs for a long time it's either not making enough pressure or the switch isn't working properly. I think the sphere is a "pressure store" Be careful there's a lot of pressure in there!
When we tested one with a pressure gauge it straightened out the hose when the pump ran up to pressure!
Cheers