You could simply use a DLookup, looking for the existence of a note for the pump id, and show the button if anything is found. Or if it would be more conducive, you could try to open a recordset and show the button if the recordset count is > 1. Which form event to use depends on how your form operates. If single record with navigation controls, then perhaps the form Current event.
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.