I suppose “pressure reducing valve” is a redundant term, since most pressure valves are designed to reduce or limit pressure in a hydraulic system. The function of this valve compared to other pressure valves is slightly different, of course. If you’ll allow me, I’ll fabricate my usual over-simplified spin to describe hydraulics you’re already well-familiar with, in my usual unique way.
A pressure reducing valve is the only “normally flowing” valve in the pressure valve library (if there are more, I have not seen them). I like to use the term “normally flowing” sometimes to differentiate hydraulics from electrics where “normally open” means there is no flow of electrons.
Under standard operating conditions (by standard, I mean the hydraulic condition which reflects how a pressure reducing symbol looks on paper…flowing), fluid simply passes through the valve like a Hollywood starlet passing the lineup, bouncer and velvet rope at an upscale night club; with little restriction. Most reducing valves allow free flow of starlets, both in and out of the club, with little or no drama, except when the Jersey Shore posse is there buying rounds of Mojitos.
When club side pressure reaches max capacity, say 3000 CPA (clubbers per acre), the bouncers stop letting more partiers in the door, and blocks incoming bodies with the velvet rope (“you’re not on the list!”). This blockage prevents club pressure from rising past 3000 CPA, and it doesn’t matter how many wannabes try to force their way in, the Shaq sized bouncers won’t let it happen. It’s not until some club-goers leave that the bouncers will allow fist pumpers to enter the club once more.
Some pressure reducing valves have a third port, called a relieving port (hence then term pressure reducing/relieve valves). When those 3000 clubbers get a little overheated, intoxicated and rambunctious, pressure in the club can appear to rise higher than what 3000 CPA would suggest, and then bouncers will start kicking dudes out the back door to relieve pressure. Be careful though; depending on the construction and layout of the club, street persons, lost clubbers or New York sized rats could be cramming up the alley, preventing relief out the back door. It’s important to keep your alley free of riff-raff to allow easy banishment of troublemakers.
Is it ironic that I once frequented nightclubs to clear my mind of daily stress and pressure, jamming myself into a sweaty dance floor with hundreds of other equally sweaty bodies, while I burned calories almost as quickly as I drank them? Oh, those were the days….