In "How To for Dummies" terms

[bp]

You are thinking in terms of pitch being measured like a prop, where the angle is what you change. What pitch refers to is how many theoretical inches with zero slip the prop or impeller will move you forward in one revolution of the unit. If you took a 28 pitch propeller and cut the back half off of it, it wouldn't be a 28 pitch anymore, even though the angle is the same. It would move half the distance, becoming a 14 pitch or something. There is less material to carry the water in both cases, so you have a reduction in pitch.
May not be the easiest word to understand considering most of us know props as pitch, but it is correct in essence...
After re-reading that, I am now not sure it is correct, because in a theoretical world with no slip, it wouldn't need to hold the water on the blade, so the pitch wouldn't change.
In any case, you are making the vane shorter, which has the same exact effect as removing pitch from a propeller.
the pitch stuff does come into play when thinking about various impeller makers. although an AA = AA, as B=B, different makers have different flow characteristics. i ran a berk B all through 2002, routinely saw 6200-6250rpm, then went to a legend B in 2003, dropped to 6000-6050, but the boat goes faster.
most pump pros have developed their own curves based on numerous impeller installs in different boats, and compiling the feedback on performance. but, to get what YOU need, you still should know what your hp curve looks like.

[inwo]

You are thinking in terms of pitch being measured like a prop, Which it is.where the angle is what you change. What pitch refers to is how many theoretical inches with zero slip the prop or impeller will move you forward in one revolution of the unit. True. If you took a 28 pitch propeller and cut the back half off of it, it wouldn't be a 28 pitch anymore, Yes it would.even though the angle is the same. Which is pitch It would move half the distance, It would move the same distance becoming a 14 pitch or something. There is less material to carry the water in both cases, so you have a reduction in pitch. No, just more slip
May not be the easiest word to understand considering most of us know props as pitch, but it is correct in essence...
After re-reading that, I am now not sure it is correct, because in a theoretical world with no slip, it wouldn't need to hold the water on the blade, so the pitch wouldn't change.
In any case, you are making the vane shorter, which has the same exact effect as removing pitch from a propeller.
That is just not true! Comparing propeller function to impeller function is not a good analogy.
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[super cyclone]

How much do they cut of to go from an A impeller to a B impeller

[inwo]

How much do they cut of to go from an A impeller to a B impeller
http://www.berkeleyjet.com/impeller_info.aspx