>would there be a new patent issued when design changes took place on the pump
Utility patents cover *functional* aspects of a thing. As long as at least one function of the pump is what was described in the patent, the patent number would be applicable to iut, and it would have some patent protection. Be carefull using the word 'design', there is a different kind of patent called a 'design patent' (not relevant here, covers just the way a thing looks)
The patent would have been good for 20 years, so untill 1939 it would apply...
>would this gentleman ( until he decided to sell the rights ) that was granted the patent for stamped sheet-metal base pumps be the only person whom could manufacture a stamped sheet metal base pump?
There are 3 questions here....
The patent grants a monopoly on manufacture, only those people he licenced can make any device incorporating the functions described in the patent.
The patent can not and does not exclude the use of sheet metal as a construction material, that is only allowed to be a part of what is described. This particular patent implies a process, which the use of sheet metal makes possible however...(If someone made a pump that worked in the same way, but used, say, thick tinfoil, it would probably infringe the patent)
The patent rights can be licenced to an arbitrary number of others, in theory, hundreds of companies could have had licences to manufacture it. (A prudent inventor would have required them to print the patent notice on them, but this doesn't always happen)
On the other hand, it is not legal to print a patent notice on something that is not in fact patented.
> if another manuf. came up with a differently designed sheet metal based pump he could also market this without issues
To be allowed, it would have to NOT incorporate *any* feature described in the patent, it would also be very risky for a manufacturer to make something that closely resembled the original, as the burden of proof shifts to them if they are sued and the object appears like the patented article...