Ev Manifold

An EV manifold (exhaust/vacuum manifold) is the facilities plumbing that distributes vacuum draw and exhaust flow from a single house connection out to multiple purge and venting points on a tool — load ports, FOUP purge stations, and EFEM exhaust — through individually valved branches instead of one shared open line. It's the part of a load port's N2-purge system that nobody designs around until it's undersized, at which point every port sharing that manifold starts purging slower than its recipe assumes.

Sizing the header is the whole engineering problem, because every branch draws on the same shared pressure. If four load ports purge simultaneously — which happens routinely when a tool's FOUPs arrive close together — each branch's actual flow depends on how much header pressure is left after the other three take their share. A manifold sized for one port's peak demand starves the others under real traffic, which shows up as purge cycles that intermittently run long for no apparent per-port reason; the fix is almost never at the port, it's upstream at the manifold or house supply.

Flow-balancing orifices exist because an unbalanced manifold doesn't fail loudly — it fails as drift. Without a calibrated restriction sized per branch, the port closest to the header (lowest line resistance) draws disproportionately more flow than the port farthest away, so purge or exhaust performance quietly varies by physical position on the manifold rather than by anything wrong with an individual load port. Facilities technicians size these orifices once, at install, specifically to equalize that draw — it's a passive fix rather than something software can compensate for after the fact.

It sits one layer below the N2-purge step in a load-port's interlock sequence, supplying the gas that sequence consumes. The purge cycle inside a load-port interlock assumes a certain flow rate is available on demand; the EV manifold is what actually has to deliver that flow, reliably, regardless of how many other ports on the same header are purging at the same moment. When a purge-time recipe gets tuned for a "fast" or "thorough" cycle, that tuning is implicitly assuming the manifold behind it can supply the flow the recipe is asking for.

The EV manifold rarely shows up on a tool's spec sheet the way a robot's cycle time or a chamber's base pressure does, but when purge-related variance shows up across ports that are otherwise mechanically identical, the manifold feeding all of them — not any single port — is usually where to look first.