Basically, all diesels need to have absolutely no air in the their system... The primer pump is a push lever system that pushes fuel through the system so you can bleed air out of it later, similar to how you bleed a brake system. On 3B's (and 2H's) the actual pump lever is known for leaking after a few years. In this case 22
Diesels have a mechanical "lift pump" similar to a 2F actually that also has a mechanical "lift pump" or fuel pump. Its only purpose is to take engine from the tank and deliver to the carb or fueling mechanism. On a diesel, the priming system I am mentioning is on the lift pump.
A little diesel tutorial if anyone is interested:
The lift pump then pushes fuel to the actual 'fuel pump,' that takes place of pretty much everything on a gasser: the carb/FI system, distributor, ignition system (plugs etc), all in one unit. Basically, gassers take in air and fuel together, compress, then use the spark plug to detonate. A diesel takes in air only, compresses that air only to more than twice the pressure of a gasser, then (when a spark plug would normally fire if were a gasser) the main fuel pump injects a tiny amount of diesel fuel in a wide spray pattern. The pressure and heat of the compressed air is so great that the fuel instantly combusts, so no spark plug required.
This is also why diesels suffer from poor starting in cold weather versus a gasser unless the engine itself and its starting aids (glow plugs, etc) are all in tip top shape. Glowplugs basically heat the fuel and combustion chambers before the engine starts and slightly when running on some models.
In between the fuel pump and the injectors are hard, prebent metal lines (usually brass) go to each injector, so 4 injectors and 4 fuel lines on a 4 cyl, 6 and 6 on a 6, etc. Then the whole think is timed very carefully to the engine via a gear so it knows precisely when to fire. The fuel pump adds more fuel (and pressure) into the brass lines to each injector precisely when the fuel is supposed to be squirted into each cyl. The injector is tuned to release the fuel at a certain pressure so it releases at the given moment the fuel pump adds more fuel to the line. And the fuel pump always keeps that fuel at a certain (usually very high) pressure. Naturally, the throttle is on the actual fuel pump this is what controls reving and power in diesels: simply adding fuel...
This is why air is bad for diesels, because it will compress and throw the whole thing off. Just like a brake line.
The main fuel pump is also surprizingly reliable for what it does, it really is the 'heart' of the system. But this is also why it is susceptable to issues like fuel properties and things like that.. Because diesels have an injector for each cyl, even a completely mechanical diesel (like a 4BT, or a pretty much most diesels before 1995-1998ish including 3B/13B-T/2H/12H-T/1HZ/1HD-T/) still act like a fuel injected gas engine in that they run at any angle and no bogging etc. This is because there is no carb to bog down. But other than that they are suprizingly similar to gas engines, they are afterall still internal combustion engines, they still have heads and valves and pistons and blocks and oil pans and all that jazz...
A guess a little tutorial on diesels...
But they sure are cool as you can tell, I am pretty into them