Filter screens look like a commodity. The mesh count is the same, the dimensions are the same, and the price is lower. Then the flow drops, or the interval shortens, or something downstream starts seeing contamination – and the cause is not obvious because nothing about the specification changed.
What differs between suppliers
- Wire diameter. The same mesh count with different wire gives a different aperture and a different open area. Both are legitimately called the same mesh.
- Aperture tolerance. Manufacturing tolerance on a woven mesh varies between sources, and the largest apertures in a screen govern what passes.
- Frame construction. Welded, overmoulded, mechanically clamped or bonded. This determines the screen’s life at the frame, which is where most failures occur.
- Seal material and compression. Different material, different life, and a different failure mode.
- Actual dimensions. Seat diameter, overall diameter, thickness. Small differences that matter at the seal.
- Surface finish and cleanliness. Residual contamination on a new screen is a real issue in some processes.
None of these appear on a purchase order that says “20 mesh, 250 mm diameter, PP”.
A proportionate qualification
Full qualification – a long trial on the real process – is only justified where a screen failure has serious consequences. For most plants, a short and structured process is enough.
Compare dimensionally. Measure seat diameter, overall dimensions, thickness and, where it matters, aperture. Compare against the existing screen, not against the drawing – drawings drift.
Compare weight. An easy proxy for material content. A screen that weighs noticeably less has thinner wire or less frame.
Compare frame construction. Cut one open if necessary. Is the mesh attachment the same method? If it was welded and the new one is bonded, that is a different product.
Run one in a non-critical housing first. Put the first new screen somewhere that a failure is inconvenient rather than serious, and watch the clean differential and the interval.
Record the clean differential. If the new screen’s clean differential differs noticeably from the old one, the open area is different and the interval will differ too.
The measurement that matters most
Clean differential pressure at a defined flow and temperature. It captures aperture, open area and wire diameter in one number, and it is the fastest way to tell whether a new screen is genuinely equivalent.
A supplier change that leaves this figure unchanged is probably safe. One that shifts it by a meaningful margin will change your interval, your energy cost and possibly your separation performance.
Managing the change
- Run both in parallel for a period. One housing on the new screen, others on the old, same duty.
- Keep the old supplier approved until the new one has proven itself. Dual source is worth the small premium while a change is bedding in.
- Update the specification with the properties that were actually verified, so the next change is qualified against something real.
- Tell the supplier what the screen does. A screen specified as a mesh count will be supplied as a mesh count. One specified with aperture, open area and frame construction will be supplied to those.
What we can do
We supply PP filter screens with aperture, open area and frame construction stated, so a comparison against an existing screen is possible on the properties that matter. Send us a sample of what you use now and we will measure it and tell you how ours differs – including where it does not match.