Here is a good video explaining the operation of the Cummins PT Pump. Even though it's a old engine some people might find it useful.
I have seen quite a few Indian movies like that explaining things I want to know about. Some of them are hard to understand the narrator but that one is pretty good. I wonder when or why it was made? The video production seems more modern than any PT stuff I have seen.
It's one of the better videos on the subject I think BV. I have had a few pm's about PT pumps and what a smaller button does, so I just refer them to this video it explains it fully. Truck Shop
It does a very good job of explaining this whole mystery that some people don't understand, but think a "bigger" button is going to get them more power.
#18 button & a purple spring.. was "the norm" for the hot rodder's around here.. usually the loggers.. That'll blow some smoke, lemme tell ya..
I remember the 1980s when the traffic light would turn green. Between the log trucks and the dump trucks you could not be sure the light had stayed green, there was so much smoke.
I remember years ago when rolling bearings in a 855 in a logger if you found the bottom rod bearings were showing signs of copper-dead give away the pump had been shimmed for 24/2500 rpm. Never mind the vise grip on the return line. Truck Shop