How Many Filter Bags Do You Need?
Start with the flow the housing must handle, including periods when production demand rises above its usual level. Sizing around normal flow alone can leave too little filtration area during peak demand.
The liquid matters as well. A viscous liquid is harder to push through filter media than water under otherwise similar conditions. When the liquid carries a high solids load, bags may fill faster and need more frequent replacement. Micron rating and filter media alter flow resistance.
Adding bags gives the housing more filtration area, but it also increases the size of the equipment and the space needed for maintenance. The right bag count depends on the required flow, the size of the bags and the characteristics of the liquid. A rated flow figure is useful for an initial comparison, but it does not tell the whole story if the actual process differs from the conditions used for that rating.
How Does Differential Pressure Affect Selection？
Solids accumulating in filter bags will push up differential pressure between the housing inlet and outlet. This is known as ΔP. How quickly it increases depends on the flow, the liquid and the filter media.
The pressure drop across clean bags is a useful starting point when comparing options. If it is already high at the required flow rate, the available filtration area may be too small, or the selected media may offer too much resistance. The bags capture more solids, rising resistance restricts flow and triggers earlier filter bag replacement.
Look at both the clean pressure drop and the expected pressure drop during operation. The filter bags have an allowable differential pressure, and the housing assembly has its own operating limits. Both need to be suitable for the intended service.
There is no single pressure-drop figure that works for every application. BOLEFIL can review the operating conditions and available performance data to help assess whether the proposed housing has enough filtration area for the required flow and solids load. Nominal flow capacity alone cannot show how the system will perform as the bags collect contaminants.
How Can You Prevent Filter Bypass?
A filter bag matched to your micron requirement won’t stop every particle from moving downstream. This can happen when liquid slips around the bag’s sealing edge instead of passing through the filter media.
The bag collar needs to sit correctly in the basket and housing so liquid is directed through the bag. The cover gasket has a different job: it seals the housing itself. A secure cover does not compensate for a poorly seated bag, and the bag seal does not replace the housing gasket.
Gasket material also needs to suit the liquid and operating conditions. EPDM, silicone, Buna-N and Viton have different chemical and temperature resistance properties. The liquid being filtered, its concentration and operating temperature all matter when choosing a housing material. Cleaning chemicals are another factor to consider.
Which Materials Suit Your Process?
Both stainless steel 304L and 316L are used for industrial bag filter housings. The liquid’s chemical composition, concentration and temperature, along with the cleaning chemicals used, determine which grade is more suitable.
SS304L may be suitable for many general industrial liquids. Where corrosion is a concern, SS316L may be a better option, depending on the chemicals involved. Gaskets and other wetted parts need the same attention; choosing stainless steel alone does not establish compatibility for the complete assembly.
Pressure and temperature requirements also need to be checked against the housing design. For projects with specific pressure-vessel codes, inspection requirements or documentation needs, those requirements should be established before the housing is specified.
What Safety Features Should You Consider?
Before anyone opens the housing, the process must be isolated, pressure fully released and the vessel drained in accordance with the operating procedure. A quick-opening cover does not remove the need for these steps.
The opening arrangement should keep the cover under control during maintenance. Depending on the design, safeguards may include a pressure-release arrangement or a mechanical interlock to help prevent opening while the housing remains pressurized. Operators still need a clear procedure for verifying that the vessel is safe to open.
What Information Is Needed for a Housing Quotation?
To quote a bag filter housing, we’ll need a few details about your process and installation.
- Process liquid: Liquid name, concentration, viscosity and solids content.
- Flow rate: Normal flow rate and Max flow
- Filtration: Required micron rating, bag size and filter media, if known.
- Operating conditions: Operating and design pressure, temperature, and cleaning method.
- Materials: Housing and gasket materials, along with any known chemical compatibility issues.
- Connections and space: Inlet and outlet sizes, connection types, and clearance above the housing for cover opening.
- Project requirements: Applicable codes, inspection requirements and required documentation.
For a replacement housing, send the existing drawings and dimensions if available. Photos of the installed unit are useful too, particularly for checking connection locations and the space available to open the cover.
