I noticed the older IP I rebuilt has shorter delivery valve that the one that came out of my 91 Jetta. I also noticed that the hard lines are different
What is the difference in the delivery valves ?
I was going to pull the valve off the '91 pump, but I see that one of the valve is missing a small shim that goes under the spring. I assume this makes a difference (may be one reason my car wasn't running all that smoothly)
delivery valves only hold a little residual pressure in the fuel lines from what ive been explained.. but can affect the running of the engine also.
BYM or Vince would have a better answer for you tho. BYM builds (built) fuel pumps, and vince just knows a little about everything..
Do a search on the site. Lots of info. I had this same question a while back, and found out what I needed to know fairly easily.