Hi Will:
I have not done this myself but it should be very possible. Might take
a trip to your local hardware to get the parts.
Pumps dont mind being restricted on their output.
On problem might be that water does not like sharp turns so that
if you are splting your 1 inch into 3 1/2s there can be more resistance
because of fluid dymamics effects.
You might what to take your 1" line into a a large (say 2") manifold
then take your 1/2s off that.

3-4" diameter manifold
-----
| |
| |=========== 1/2" lines
| |
============= |===========
1" line | |
| |===========
| |
-----

My opinion stems from trying to irrigate a hilside with a 2" gas powered
pump from a stream. It pushed a lot of water but we simply put in a
tee every so ofter for a garden hose like. Surprisingly little water
made it out those lines - too much resistance taking a 90 deg bend into
that small diameter pipe.

Good luck.

Will James wrote:
Hello
can someone tell me if it is possible to use 1/2 inch nozzles on 1 inch
pumps i.e. the Oase Aquarius 5000 E
http://www.water-garden.co.uk/pump_aquarius.php
if it is possible, would it work well + would I need some kind of adaptor? I
am thinking of running two or three 1/2 inch fountain nozzles on the above
pump- would the flow to each fountain be roughly 1/3 of the total flow,
therefore presumably a shorter fountain height?

Thanks

Will