| http://www.w3.org/ns/prov#value | - A valve as claimed in claim 1 wherein the closure member in the body is a transversely contractable and expansible tubular member having an internal bore of which defines at least part of the first flow passage, wherein the varible volume chamber is located immediately externally of the tubular member and wherein the chamber communicates with suction pressure externally of the tubular member.
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