[MrSafety]

Crazy Rabbit,
Yes, the "Case Pres." comes from the
1st-Stage Rotary-Vane pump...
and it is regulated by two components:

(a) one next to the IP's fuel inlet fitting...
Pressure-control valve ~$30
The pressure-control valve is connected through
a[n internal] passage to the upper (outlet)
kidney-shaped recess, and is mounted in the
immediate vicinity of the fuel-supply pump.
It is a springloaded spool-type valve with which the
pump’s internal pressure can be varied
as a function of the quantity of fuel being
delivered.
If fuel pressure increases beyond a given value,
the valve spool opens the return passage so that
the fuel can flow back to the supply pump’s
suction side. If the fuel pressure is too
low, the return passage is closed by the
spring.AND

(b) the other at the fuel return fitting.
Overflow restriction - Less than $30...
and rarely fails... just clogs up!
The overflow restriction (Figure 6) is
screwed into the injection pump’s
governor cover and connected to the
pump’s interior. It permits a variable
amount of fuel to return to the fuel tank
through a narrow passage. For this
fuel, the restriction represents a flow
resistance that assists in maintaining
the pressure inside the injection pump.
Being as inside the pump a precisely
defined pressure is required as a function
of pump speed, the overflow restriction
and the flow-control valve are precisely
matched to each other.

IF not already available via this FORUM,
I can forward to you an excellent Bosch 101
instructional booklet (PDF file) that does a great job
of explaining these and also has very good graphics!
It's title is:
"Diesel-Engine management;
Diesel distributor fuel-injection pumps"
and is ~60+ pages... 4th Ed. ... last released in 1999
bright yellow cover !
Let me know if you want a copy
of this PDF file... less than 2mb
Regards,
Sam Ross