I see it posted a lot here about an elbow being worth "x" amount of head loss. It's worth noting there's no hard figure for the head loss through a certain fitting. It's a function of the pipe diameter, the flow rate, and the individual fitting.
Most of what you'll find on the internet for
PVC pipe and fittings is given in equivalent pipe lengths, which may be why there is confusion. For example, a 1"-45° elbow is equivalent to an extra 1.3 ft of pipe---NOT 1.3 ft of head. A 1"-90° is equivalent to an extra 2.6 ft of pipe. The actual head loss is based on the system flow rate:
At 600
GPH (10 GPM), the above 45° gives only 0.08' of head loss. The 90° loses only 0.16' of head.
The best (read: simplest) site I've found is here:
http://www.valler.com/fish/tips.html