Pressure regulators come in several types. I will review them here. Also age is a factor, Will comment later in post
Small (about 3/4 Inch) Cylinder male connection on one end female on other WITHOUT wings or bright plastic grip... PURE JUNK, can not do 1GPM well
Same with wings on body or Bright plastic grip Still JUNK Does one GPM, you need at least 2.5 to be good.
Note, Above may be brass or plastic
Sur-Flo.. When new I give this one a 9.. (Just shy of 2 GPM flow rate) But See below.
Valterra Adjustable: I have not personally tried, Others say nice things
Watts, 1/2 inch or larger, Also Zurin 1/2 inch or larger
These are designed to be installed in a house.. They have a bell shaped upper housing with a bolt where the "hanger" on a bell would be (or the handle on a hand bell) this is the pressure adjustment.. Mine are 3/4 inch
I give both of them a resounding 10 when new
But From Sur-Flo on as they age.. Well you know the joke about Bo Derrek getting older (10-9-8-7-.....1) Applies to these.
BUT.. They can be rebuilt. I've still got to get a rebuild kit but they can be rebuilt. Easily and cheaply
Exception: I have not actually held one of the Valterra units in my hand so I do not know if it can be rebulilt or not.. Guessing it can but not sure.
All of them though as they age become more "Restrictive" of flow.