Pressurized Tubes randomly stop transporting gasses. They're only used to transport gasses from Mekanism machines to others and only over short distances of 2-4 blocks. They will still display the "filled" texture of the gas they are supposed to transport, but no gas arrives at the target machine and the tank in the source starts filling up. Changing the connection type or redstone sensitivity does not help. Breaking and replacing the tube (any block of a connection) restarts the transport, but eventually it will stop again.

Happens in Mekanism-1.7.10-7.1.0.88

EDIT: This used to work in an earlier version (unfortunately I don't remember which one)

This was fixed in 7.1.0.89.