Water pump blockage

Having dismantled my water pump to try and discover why it's not pumping, I have discovered a rubber ball lodged in the T-piece taking the water from the pump to the clack. My engine is fitted with a hand pump too and the T-piece takes the water from the hand and mechanical pumps to the boiler. The rubber ball clearly shouldn't be there as it's preventing the mechanical pump from pumping water to the boiler but I don't know how its got there. Presumably it has come from one of the pumps or the clack valve?

thanks,
James

After stripping it all down, I've discovered that the clack valve had no bearing in it so I assume that the nitrile ball was put in there and had been sucked up towards the pump at some point. It's hopefully all sorted now and I can steam it up at the weekend to test it out.