I am trying to get some information on double-hung vinyl replacement
windows. What I am trying to learn about are the various mechanisms for
raising and lowering the window sashes.

Is it true that the trend is toward getting away from having any mechanical
balances in vinyl replacement windows? Instead, I have heard that the newer
vinyl replacement now use an adjustable friction type system with no tubes
or spirals, etc.

I am wondering about this because I keep running into vinyl windows in
different properties where the "balances" (or whatever they are called) are
broken, have missing parts, don't work correctly, etc. Yet, when I go to
websites like http://Pella.com I can't seem to find any clear information
there about this.