Service kit ( Special Piston, plus Seals & Spacers ), for 2510 Air Draw Valve Assembly,
For Air Injection versions of the Fleck 2510 valve ( not for normal Filter or Water Softener applications ).
Stuffer Tool ( 11098 ) recommended for replacing the Seals & Spacers.
For more about AIO systems,
see this FAQ Article = AIR INJECTION OXIDIZING FILTER SYSTEM = AIO
Here is a LINK to AIO system ( AIR INJECTION OXIDIZING FILTER SYSTEM ) as sold by Nelsen Corporation = https://www.nelsencorp.com/customer/docs/SKUDocs/Nelsen-AIO-Manual.pdf
** Item has been discontinued by manufacturer,
Pentair is directing everyone to use piston 60090 & Seals & Spacers 60121