Here are six different O&R pumps. I don't know how many different ones were produced though I have seen at least 2 more. 
  
The blue one has no nameplate. Going clockwise from there they are a Keene Engineering, a Cenatron, a Kenco, a Comet and an ElectroFlow. 
  
I never cease to be amazed by how many different companies used these little engines.