The pump has a diaphragm just for the vacuum end of the pump.(top end of the pump).It should be rebuildable /replaceable. I am not sure who offers a rebuild kit, You may have to get some reinforced material and make/cut a diaphragm or at least take it apart and inspect it. It COULD possibly have a stuck check-valve.

There is enough good in the worst of us and enough bad in the best of us that it does not behoove any of us to criticize the rest of us.
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Be yourself. If you are ever lost, It will be much easier to find yourself if you know who you are!