In a nutshell, I designed a water pump and I want to get a patent for that. I found that other patents have similarities of about 80% as my design. The main differences of my design is angle of blades is different, so the compression is different, internal volume is different, bearing fixed to the mid axis is different than other patented designs (but the bearing used is not a my invention). And the pump shape is slightly different. Material used is similar as I also use steel, iron, titanium and aluminium for internal parts. So, the basic idea is same. Same principles are used. But the machine is not identical to any of other patented machines. But after-all it will pump water like other patented machines. So in this case do patents cover the idea and basic principles? or the specific materials used or the technology such as slightly different shape, different blade angles etc?
A patent covers what the claims specify. In general, the claims aren't specific to a single implementation, but cover as broad a description of the novel idea as allowed by the examination process. You do sometimes see ranges specified for certain items, but not always and sometimes only in dependent claims. In order for your design to get patent protection, there needs to be something novel over the prior art. Merely tweaking some design aspect to optimize performance is likely not sufficient to obtain a patent. It would be considered "obvious" which means someone with ordinary skill in the field is likely to think of the change. If you make a change which results in an unexpected benefit, then you have a greater chance of getting the improvement patented.
I don't want to discourage you from trying to obtain a patent. I don't know enough about your design and the prior art to do that. What I would say it to focus on the specific improvements and try to patent those. For example, from your description is sounds like the impeller is more effective. If you can describe specific design differences with your impeller from what has been used previously, you may be able to get a patent on those differences. The trick is to not get so narrow with the claims that someone can avoid your patent with trivial design changes.
Patent claims can be broad or narrow. Sometimes, the basic concept, speaking very loosely, is so novel/non-obvious that one can get a broad claim. Other times you need to narrow and narrow to a specific embodiment to get a claim allowed. In that case the patent might not be worth much if someone can leave out a detail you needed to achieve patentability with little loss of customer appeal.