Matched context for prevent back and obstruct

The page lists matched contexts for prevent back and obstruct.

Share - prevent back	Share - obstruct	Phrase
22.16%	12.58%	{prevent back or obstruct} flow [perform operation]
16.84%	4.02%	valve [does] {prevent back or obstruct}
7.78%	0.90%	{prevent back or obstruct} fuel [perform operation]
4.86%	0.87%	substantially [degree] {prevent back or obstruct}