How pressure regulator work ?

Dear All,
Just i want to know the working principle of the regulator,please find the attachment.Any one clearly tell the function of spring in this regulator .In this pressure regulator how the pressure is increasing,Is it by the spring force or by orifice action?What ever it is please explain me clearly.My questions are 1.Is that spring compressed or moved ?2. what is the role of spring 3.whatis happeneing when the handle turned clock wise and anti clock wise ?I am student and also a beginner to this .Please clearly explain whats happening see the attachment the question is about that,,,,......[IMG]http://www.engineersedge.com/engineering-forum/attachment.php?attachmentid=1515&stc=1[/IMG]

A pressure regulator limits excess inlet water pressure to a constant outlet pressure. You need constant outlet pressure to ensure that your sprinkler (or emitter) performs well.Water travels through the inlet end of the regulator and around a fixed seat into the critical flow area. The water then enters into a hollow cylinder called a throttling stem (or T-stem) which is attached to a larger diaphragm near the outlet end. A spring around the throttling stem tends to hold the flow area open, while water pressure acting on the total diaphragm area tries to close it. This duel always ends in a draw with the outlet (or regulated) pressure being determined by the spring’s compressive strength.