impaler vanes

If no one has specified the number of impeller vanes, the pump should be acceptable so long as it meets the other, more relevant, parameters.

If someone has specified this number, then you should seek approval for any substitutes.

This may all depend on the precise wording of various documents such as engineering specifications, purchase orders, contract terms, and regulatory codes.

By the way, many vendors may suggest product specifications that--guess what--fit only their product. These have no force unless someone in charge actually adopts them.

Practically it should not be a problem, More are the number of vanes better is the performance, provided added vane don't eat too much of free space between vanes, So it is a trade of between number of vanes and space between vanes, theoretically if van thickness approaches to zero Number vanes can approaches to infinity, however never possible practically.