Family treasure said pneumatic weaver (8)
I believe the answer is:
heirloom
'family treasure' is the definition.
(I've seen this before)
'pneumatic weaver' is the wordplay.
'pneumatic' becomes 'heir' (I can't explain this - if you can you should give a lot more credence to this answer).
'weaver' becomes 'loom' (I've seen this before).
'heir'+'loom'='HEIRLOOM'
'said' is the link.
This may not be right. It may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for heirloom that I've seen before include "Treasure handed down in family" , "Hand-me-down" , "Valuable family object" , "Long-time family possession" , "Treasured family possession" .)