Water Pressure Regulator

Hey Folks, I'm going to install a Water Pessure Regulator. A local hardware store has a WATTS N55B-M1 for $45, is this a good quality product? Who makes good ones?/what do I look for???
The instructions on the Watts say to install a Backflow Preventer before the Regulator, is this important/ a waste/ trouble/ ???? if I do, what are the requirements? certain distance between the two? certain distance between Preventer and Meter??? anything I'm not asking???
What about an expansion tank or a pressure relief valve?( Watts 530C ) will i need one of these?/ which one??..........

Thanks again,
Steve

Watts is a good brand of plumbing supplies. The use of pressure regulators and expansion tanks is a frequent topic here, but this is the first time I've heard of a backflow preventer being installed. They are used when teeing off of a domestic system for irrigation, which is certainly not what you are doing. In fact, a pressure regulator is a backflow preventer and creates a "closed system). Heated water expands, and in a closed system this creates pressure. The pressure regulator prevents this expansion from being absorbed by the water supply. The result is the TP valve on the water heater will trip to relieve this pressure. This is why you need to install an expansion tank when you install a pressure regulator.

Thanks Gary.
The Watts website is really great, gave me lots of good info. One thing it showed a "Vacuum Relief Valve" at top of water heater, I've not seen these before, is this necessary??? Thanks again...

Similar to the Watts picture... the way it is done here... shut off valve-water meter-check valve/backflow preventer (supplied by water department) - regulator (supplied by customer).
I've only seen one water heater with the vaccum relief.... I've seen so few of them that I still don't understand their use... I'll post a topic on that.

watts

The heater is to show all the Watts products you could use on the water heater. But it is not a "real" installation because, if you notice, the cold water from the meter only goes to the water heater, so the house would only have hot water, and there is no shut off valve on the cold supply to the heater. DO NOT always depend on some engineer's idea of how to plumb a system. They often deal in theories, not practicallities.