What Do You Know About Liquid Filter Bags?(二）

Jan 27, 2026

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In the previous article, we discussed the construction of liquid filter bags. This article will guide you on how to sew an excellent liquid filter bag.

Sewing Process for Liquid Filter Bags

I. Preparation of Materials and Tools

Select materials compatible with the filter media (PP/Nylon/PTFE filter cloth) and matching sewing thread (thread diameter ≥ 210D). Gather the necessary components: top ring, bottom pad, and an industrial heavy-duty sewing machine (preferably a synchronized machine). Use 16-18 gauge needles, adjust the stitch length to 2.5 stitches/cm, and prepare additional tools such as fabric cutting knives, measuring tapes, and a low-temperature iron.

II. Cutting and Pre-treatment

Cut the filter cloth for the bag body and bottom according to the finished dimensions, leaving a 1.5-2 cm seam allowance and reserving 3-5 cm at the top opening for securing the top ring. Smooth out the filter material with a low-temperature iron (except for PTFE material) to avoid wrinkles. For high-precision filter materials, use heat sealing to trim and prevent fraying after cutting.

III. Core Sewing Steps

1. Sewing the Bag Body: Sew the side seams inside out, aligning the edges, and use double stitching with a 0.3-0.5 cm spacing between rows. After sewing, turn the bag right side out and check for skipped stitches.

2. Attaching the Bottom: Align the bottom piece with the bag body, baste to secure, and sew two concentric rows of stitches around the bottom. Reinforce the corners with an additional 2-3 stitches.

3. Installing the Top Ring: Fold the top edge over the ring and secure it with two concentric rows of stitches. For high-demand applications, add a heat-sealing tape and apply heat pressure for an extra seal.

IV. Finished Product Inspection

Ensure the bag is free of wrinkles and has continuous, even stitches. Conduct a pressure test at 0.3 MPa to check for leaks. Verify that the dimensions fit the filter housing properly. Finally, rinse the bag to remove any loose fibers and allow it to dry.

Key Pitfalls to Avoid

Always use double stitching and ensure the thread material matches the filter cloth. For high-precision filter bags, employ heat sealing to prevent leaks. Avoid liquid leakage and fiber shedding through careful execution.