Looks like a single to me
Greetings Super Turtle,
From the design alone it appears to be a single diaphragm pump unless there is a dual action that they have, but can't image how the air would leave the engine side of the diaphragm to do any good. Just looking at the housing it appears that the small bell contains the diaphragm and the rectangular cover on the end must cover up probably reed valves to control direction of air. Think that's right? Can't image having to replace them as well but for sure the leaking diaphragm.
Any other input? Do you have this in your manual? Hopefully my cd will arrive any day now and clear alot of what is left out of the Haynes, Chilton, and other Chilton manuals. Do these diesels seem slow to accelerate or is it just my imagination?