Sounds like the piston type is the newer version. I suspect it is the better design. I have had experience with airless sprayers and the piston types are the only way to go. I rebuilt my pump, the old diaphram was not damaged but worn. Sounds like the pumps are interchangeable but I would verify it with some one more knowledgable. I pull about 15in of vac which is spec for my model. I am planning a trip to the salvage in a few weeks. I'll try to pull some pumps for comparison.