If the poppet on your keg is faulty, it is relatively simple to replace.
If you're unsure if this poppet will work with your keg, try the 'Universal Poppet'.
Three Piece Airlock
Star San Sanitizer - 16 fl oz (473 ml)
Cascade Hop Pellets - 1 oz (28 g)
Safale US-05 Yeast