Main venting

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Problem is in 200 unit apartment building with very long mains, and it is a two pipe, pumped return, no water seal, system.

Can I vent the top of the supply risers as in Gerety, where needed?

Do I vent the supply at the end of the main or at the end of the dry return, as needed?

Unknown

You have an open vent on the tank

The traps on the mains should vent the air to the tank, which has a wide open vent pipe on it (in theory)

Make sure there are no water seals in the return line to the tank, so that it can vent the system unrestricted.

Noel