... we're talking about filling a 100 gallon tank..at 1/4" it would in theory take twice as long as the 1/2" line I'm currently using...right? ...

No. A 1/2" line is FOUR times as large as a 1/4" line -- remember that cross-sectional area of a circle varies with the square of the diameter. So at the very best, it would take four times as long. In practice, it takes even longer, because as the diameter decreases, the ratio of the surface area of the pipe to the volume of the pipe also increases, and flow rate at a given pressure will be lower. That calculation depends on the material of the pipe, number of bends, etc., and is more complex than we need to go into, other than to say you should figure it takes more like five times as long to deliver a give quantity of fluid through a pipe half the diameter.

To elaborate on what John wrote, at most city water fills, it takes us 20 minutes to fill our 135-gallon tank through a 5/8" hose (the smallest diameter in the system). If we added a 1/4" restriction to that line I would figure it to take more like an hour and a half, up to two hours.

This is one reason why I tell folks to make sure they understand orifice diameters when they are buying valves. Lots of solenoids on the market, for example, will have 1/2" inlet and outlet fittings, but a much smaller orifice, some as small as 1/8".

FWIW.

-Sean

http://OurOdyssey.BlogSpot.com