Matched context for penetration and back-flow

The page lists matched contexts for penetration and back-flow.

Share - penetration	Share - back-flow	Phrase
3.13%	27.51%	prevent {penetration or back-flow} [perform operation]
4.11%	6.55%	fuel {penetration or back-flow}
0.84%	6.12%	gas {penetration or back-flow}
0.77%	7.24%	oil {penetration or back-flow}
0.56%	4.08%	air {penetration or back-flow}