Stepped end-cover of the capacitor quenched pump

Diode with red and black wires connected between the points and the 12v supply, i.e. effectively across the solenoid winding. This is a negative ground pump, a positive ground pump would have the red and black wires reversed. Diodes do seem to me more effective at quenching, I can still see very slight spitting on the capacitor quenched, but nothing at all on the diode quenched. However having refurbished both types the physical erosion seems to be exactly the same!

End-cap with a half-cylindrical raised portion instead of the step. Bear in mind the end-caps are interchangeable, and I see no reason why they could not be swapped over between pump types, so you really need to look under thae cap to see if there is a diode and which way round it is connected to be sure what you have.

Metal-oxide varistor of the type giving dual polarity quenching in the later version of AZX1331, at least. Image from Wikipedia

Plastic-bodied Moprod pump, same pipe fittings mounting arrangements as the SU so an easy swap. Even though these contain electrincs there is only one version for both polarities of car as both electrical conenctions are in the end cap - +ve and -ve. Clearly marked and you need to get them the right way round for the pump to operate, but there is a series diode to protect the electronics against reverse connection, in this case the pump simply won't operate until it is connected correctly. No vent ports, so existing vent tubes should be tied up out of the way ready for refitting a 'proper' pump!

Internals showing the electronic components and the magnet on the end of the diaphragm shaft (this is the 'unused' end, it is the other end that passes across the magnetic reed switch as the diaphragm moves to open and close the switch). The quench diode performs the same function as the quench capacitor and diode in points pumps but to protect the transistor from the back EMF of solenoid winding. The resistor biases the transistor to switch off in the absence of a signal from the closed reed switch. The protection diode isolates the electronic components in the even of the power supply being connected the wrong way round. The varistor connection is curious. A varistor is normally high resistance in both directions, but when the voltage across it in either direction exceeds a certain value (18v in this case) it 'breaks down' to a relatively low resistance. As such it can be used to protect points-type pumps, which means that they will no longer be polarity sensitive as diode-protected pumps are. So far so good, maybe it is just another quench or protection against spikes from the supply, but it is connected between the -ve terminal and the heat-sink for the transistor/mounting plate for the reed switch, with no apparent electrical connection to those or anything else.

Showing the reed switch pegged, glued and screwed at a specific angle. What isn't apparent on this pump is the 'hysterysis' that exists in the design of the points in that type of pump. This hysterysis ensures that when the solenoid is energised and moves the points, they don't open until the diaphragm has reached nearly full travel. When they do open the solenoid is de-energised, so the return spring on the diaphragm starts to move it back again (and pump fuel), which moves the points back again, but they don't close again until the diaphragm is nearly fully returned. This prevents the diaphragm 'fluttering' with a very small amount of travel back and fore which is what would happen if the points opened and closed at the same physical position of the diaphragm. As I say I can't see this in the physical design of the Moprod pump, other than the fact that a reed switch requires less magnetism to keep the contacts closed than it did to close them in the first place. The problem I had with mine was that the diaphragm did start to flutter, i.e. very short travel back and fore, which caused severe fuel starvation, would start and stop doing that for no reason that I could see, and once started nothing I did would make it start working properly again until it decided to do so for itself. Which is why it now languishes on the bench and is only used as a very short-term spare.