No pressure buildup model O2OP10, what do I do?

It sounds like you might need to relubricate the pump by applying 10-12 drops of light oil down the pump rod through the opening in the cap. Also you will need to inspect the o-rings and gaskets because they can become brittle. Apply petroleum jelly liberally or replace. Lastly, the check valve on the bottom of the pump might need to be replaced if it is not getting a good seal. If these steps do not fix the issue, please contact us at 1-800-311-9903 so we can continue to troubleshoot the problem and provide a solution. Thank you Tom.