Isn't there an internal metal cap above the diaphragm? Wouldn't that serve to limit the travel of the diaphragm during manual operation? I've performed this operation with no (apparent) harm to the pump on several occasions. Attachments (if any) are scanned with anti-virus software. Later, JR '61 Rampside Standard 4/110 '65 Monza Convertible 4/140 '66 beater Coupe - icemobile 4/140