---
title: "Bag cage"
description: "A bag cage is the welded wire frame that holds a filter bag open against the differential pressure of a pulse-jet baghouse. Without the cage the bag would collapse inwards on the dirty-gas side and block flow. Cages are typically galvanised carbon steel, with longer-life options in 304 / 316 stainless for corrosive duty."
canonical_url: "https://sylio.co/glossary/bag-cage"
last_updated: "2026-06-28T02:29:24.080Z"
---

A **bag cage** is the welded wire frame that holds a [filter bag](/glossary/filter-bag) open against the [differential pressure](/glossary/differential-pressure-baghouse) of a [pulse-jet baghouse](/glossary/pulse-jet-baghouse). Without the cage the bag would collapse inwards on the dirty-gas side and block flow. Cages are typically galvanised carbon steel, with longer-life options in 304 / [316 stainless](/glossary/aisi-316-316l-stainless) for corrosive duty.

## Construction

A standard cage has 8–20 vertical wires welded to top, bottom and intermediate rings. The top ring carries the venturi assembly through which the pulse-jet air enters; the bottom is closed with a disc. Cage diameter is fractionally smaller than the bag's inside diameter so the bag slides over it without bunching.

## Cage-related failures

- **Corrosion** — galvanised steel attacked by sulphurous or chloride-rich gas
- **Wire breakage** — usually at weld points after thermal cycling
- **Loss of roundness** — distortion under uneven cleaning pulses
- **Venturi loss** — separates from the cage top, reducing pulse penetration

A failed cage typically destroys the bag within hours of detection.

## Related terms

- [Filter bag](/glossary/filter-bag)
- [Baghouse](/glossary/baghouse)
- [Tubesheet](/glossary/tubesheet)