“Polypropylene filter bag” does not automatically mean “pre-wet before use.” The requirement depends on the exact media construction. Some high-efficiency polypropylene microfiber bags are hydrophobic and are supplied with a defined aqueous pre-wetting instruction; many conventional needle-felt or monofilament products are specified and started differently. A procurement team should therefore ask for the manufacturer’s product-specific startup procedure instead of applying one generic rule to every PP bag.
This guide turns that distinction into an RFQ and commissioning checklist. It is intended for engineers purchasing PP filter bags for aqueous service, especially where an initial wetting issue could be confused with excessive pressure drop or poor flow.
First identify the exact media, not only “PP”
Ask the supplier to state the media family, construction, nominal or absolute retention basis, number of layers, surface treatment, bag size, collar type and recommended flow direction. Eaton’s PROGAF and ACCUGAF literature specifically describes hydrophobic polypropylene microfiber media that requires pre-wetting with an aqueous solution. That is a product-family instruction—not proof that all polypropylene bags require the same treatment.
For a standard RFQ, record whether the proposed bag is needle felt, monofilament mesh, multilayer microfiber or another construction. If a supplier proposes a substitute, require a new wetting declaration. A change from one PP construction to another can change startup behavior even when the stated micron rating is unchanged.
Define the process liquid and startup condition
- Liquid name, concentration, pH and temperature at startup and normal operation
- Whether the first liquid is water, product, solvent, cleaning solution or rinse
- Viscosity and surface tension information when available
- Permitted pre-wetting liquid and maximum allowable carryover
- Minimum and normal flow, inlet pressure and available pump head
- Required cleanliness, extractables or food-contact documentation
Do not select a wetting liquid from a generic internet recipe. The filter manufacturer and the process owner should approve it for the actual fluid, safety data sheet, downstream product and disposal route. Where water or another aqueous solution is specified, the supplier should state concentration, contact time, drainage and rinse steps.
Plan a controlled startup trial
- Confirm the bag part number, lot and correct installation in the restrainer basket.
- Record clean-system differential pressure with the housing empty or with the approved reference element.
- Apply only the supplier’s written pre-wetting instruction for that media.
- Vent trapped gas and introduce liquid gradually within the housing and system limits.
- Record flow, inlet pressure, outlet pressure and differential pressure at fixed intervals.
- Inspect for bypass, leaks, abnormal bag movement and unacceptable carryover.
- Retain the startup record with the bag lot and change-control documents.
Differential pressure is the difference between inlet and outlet pressure, not the housing’s operating pressure. A high initial differential pressure can have several causes: incomplete wetting, trapped gas, a closed valve, wrong flow direction, a collapsed or poorly supported bag, unexpectedly high viscosity, or a restriction elsewhere in the line. Troubleshooting should check these causes systematically rather than assuming the media is defective.
What the supplier should include in the quotation
| RFQ item | Required response |
|---|---|
| Media identification | Construction, polymer, layers and retention basis |
| Wetting declaration | Required, not required, or conditional for the quoted part number |
| Procedure | Approved liquid, concentration, time, drain and rinse steps |
| Operating limits | Temperature, differential pressure and flow guidance for the supplied bag |
| Compatibility | Statement based on the disclosed process liquid; trial limitations noted |
| Traceability | Lot code and certificate options |
| Fit | Bag size, ring/collar and housing interface |
For a replacement project, send the existing bag label, photographs, dimensions and current startup procedure. If the existing element is a proprietary high-efficiency bag, do not approve a cross-reference on micron rating alone. Compare construction, efficiency test basis, seal interface, wetting instruction and clean pressure drop.
Build acceptance criteria before the trial
Useful acceptance criteria include stable flow at the defined temperature, a documented clean differential-pressure baseline, no seal bypass, no visible leakage and downstream quality that meets the process owner’s test method. The trial protocol should also define how long the bag is conditioned before samples are taken. Avoid promising a universal pressure drop or service life: both depend on viscosity, contaminant loading, flow, bag area and the housing.
If the application needs a different construction, review PP needle felt versus monofilament mesh and ring and collar fit before issuing the purchase order.
Request a startup-ready quotation
Send Your Specification with the liquid, temperature, viscosity, bag size, collar, current part number, target retention, flow and permitted wetting liquid. Ask INCE to return a quoted construction, fit confirmation and a product-specific wetting declaration. A sample trial is the appropriate way to verify performance in the real process.
FAQ
Do all polypropylene filter bags need pre-wetting?
No. The requirement depends on the exact media. Certain hydrophobic PP microfiber products require an aqueous pre-wetting step, while other PP constructions may have different instructions.
Can alcohol always be used to pre-wet a PP bag?
No. Use only a liquid and procedure approved by the filter supplier and process owner for the specific product, safety requirements and downstream process.
What should be recorded during commissioning?
Record bag part and lot, startup liquid and temperature, flow, inlet and outlet pressure, differential pressure, venting, conditioning time and downstream acceptance results.
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