| http://www.w3.org/ns/prov#value | - These passages may be formed between bottom and top disk shaped portions 15 and 16 of the impeller by spacing means or members 17. which are secured-to said upper and lower dish shaped portions .15 and 16 preferably in such manner as to enable adjustment of said spacing members to vary the size and shape oft-he outlet openings of the outwardly extending channels 1 1 aforesaid.
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