primer pump

[JAM]

I guess it has to do with the mesh, but the exact role of diaphragm marked U?
Someone can explain me?

Thanks.

[CaptonZap]

[JAM]

I try to build this system (never in my life I've had it in my hands, and I've seen him physically) so I turned to photographs, diagrams and parts list to determine dimensions, features and achieve develop construction drawings for such end.

I turn to their knowledge to query a couple of questions regarding the plunger.

. 1 - what material are constructed glands?
2 -. Equally, which is the material the four packing rings?
. 3 - and cup?

As to external dimensions, I think not having doubts, I usually work on photography or outline drawing, once the scale determined by a dimension known beforehand.

Thank you very much for your help.