It's a not-quite ordinary diaphram pump
, in that both sides of the central diaphram are pumps - it's really two pumps, one on either side with the diaphram in the middle. Overhaul
1. Is the diaphram intact and flexible?
2. Are the seals
around the diaphram sealing and not letting air (your prime) in?
3. Are the one-way valves similarly intact and flexible,
4. is there any junk (organic crud, the wrench you lost
in the bilge) letting the one-way valves be two-way, as in a heart murmur?
bstreep is right. You have nothing to fear in tearing it down but perhaps messy fingers from silicone sealant
, and then you'll know how it works.