A repair kit for Pumptec brass pressure regulator. 
KIT, REGULATOR REPAIR WITH STAINLESSSTEEL SEAT
The most common repair kit for Mytee, Century 400, Ninja, Clean Storm, Speedster, EDIC Galaxy, and Kaivac
250 to 500 psi
Fixes regulators PT020, PT021, PT021s, MV500, MV510, Mytee C313C, EDIC G03523-1

Also marketed under part numbers:
PT020A,  
C-500/510-KIT_RR,
Pumptec 70002
Century 400  250-33A,
Prochem 8.619-924.0,
Windsor 86199240

Receive half price shipping by picking up at Steam Brite San Antonio, TX 78233

Please note in the video that the repair tech does not tell you the importance to make sure that while inserting the piston, you need to make sure that the square "o" ring does not fold back on itself.  The "O" ring is cupped shaped and most people ruin the Oring by too quickly inserting inside the hole.  I like to use a dental pick or ultra small screw driver to make sure you depress the Oring downward as you go into the hole.  Work the dental pick around the O ring to make sure it all faces forward as you push it forward.