Here is an academic description of volume vs pressure
- because it is academic, the pressure in the system is constant. i know my well-fed house cycles - drops to 45psi, then up to 60psi, but ignore things like that.
And ignore friction in the pipes, and poorly designed turns and Ts.....
think of a bowl of water - the pressure is equal across the flat bottom of the bowl and proportional to the depth of the water (doesn't matter how big the bowl is, only how deep, linear proportion)
put a pin hole in it and the pressure delivered by the water is the same as if you peeled the bottom off
at the instant of opening it - the pin hole would only allow a small volume to get by, while the large opening would allow alot more (this geometrically proportional)
Now consider that there is a water supply to the bowl that matches the outflow, no matter how big or small the opening without changing any other variable (if it were a waterfall, it would impart force on the top of the water - so just say it magically maintains the level) - thus constant pressure, variable flow - you do it everyday with your kitchen sink - the lever makes variable flow!
we haven't even started talking about velocity (inversely proporional to the hole size) - which is really what people want coming out of their showerhead.
the pin hole shoots the water because of initial velocity. think of a showhead that passes 2.5 gpm but only has one hole, vs one with many small holes also 2.5gpm. remember pressure is constant (and drops to 0 as soon as it leaves the opening)
don't think of your supply as being pumped, think of it as a big tank on the hill, it has no velocity, infinite volume, and fixed pressure.
As an aside: our homes are not an academic exercise, and professional experience puts the theories to work , with all the tweaking they need to work in the real world.....
any help?
pat
here is the bridge to electricity - maybe that will also help
from
http://www.thebugshop.org/bsfqelec.htm
The Water Connection
I love a good analogy. And the electricity/water one is one of my favorites, but it does have its shortcomings, so bear with me.
Think of electricity as running through a wire as water runs through a pipe. This can really help it all make sense. Now, lets equate some basic terms:
VOLTS: This is how fast the water is flowing through the pipe, ("Voltage")
AMPS: This is how much (volume) of water flowing through the pipe, ("Current")
POWER: This is force that the water in the pipe can exert (read on, it'll make sense)