Inside a Wedge Wire Screen: What the V Profile Actually Does

Everyone in the trade calls it wedge wire, because the profile looks like a wedge in cross section: wide at the top, narrow at the bottom. That shape is doing three jobs at once, and none of them are obvious from a photo of a finished screen.

Why the Slot Opens Outward

In a wedge wire screen, the profiles are welded to support rods and spaced apart to leave a slot. Because the profile tapers, the slot is narrowest at the surface and wider behind it. Particles smaller than the slot go straight through. A particle that enters but does not fit keeps moving into the wider part and drops away instead of lodging there.

That is what people mean when they say the screen backwashes clean. Punched plate cannot do it. Its holes are straight-sided, so anything that half enters stays, and eventually blinds the screen.

What the Profile Angle Really Controls

The included angle sets how quickly the slot opens behind the surface. A sharper profile opens slowly, so the screen behaves closer to a straight-hole screen and holds a tighter cut. A blunter profile opens fast, which helps with sticky or fibrous material and with backwashing, but gives up open area at the surface.

Two consequences follow, and they are usually why a buyer and a screen maker end up arguing over the profile drawing:

• Open area. For a given slot, wider wire at the surface means less open area. If capacity matters more than cut precision, you change wire width, not slot.
• Strength. The apex has to survive pressure drop and cleaning. Too sharp a tip deforms under load, and once it deforms the slot has moved for good.

Where ±0.02 mm Shows Up

The slot is set by winding pitch and by the width of the wire at the surface. If the wire width wanders through the coil, the slot wanders with it. A screen with uneven slots has zones that blind early and zones that pass oversize material, and no amount of inspection at the end fixes that.

This is why the tolerance belongs on the profile and not on the finished screen. Hold the control dimension at the drawing, and the slot on the finished cylinder is where you planned it.

The Apex Radius, and Why Drawings Disagree

Drawings usually call out an apex radius, and it is the number people skip. Too small and the tip wears or chips during welding and cleaning. Too large and you lose open area and blunt the cut point. It also has to be repeatable: if the radius grows from coil to coil, the same slot setting gives you a different effective opening on the next screen, and your inspection data stops meaning anything.

Material in Practice

304 covers municipal water and general industrial filtration. 316L is the coastal, brine and food-grade choice, and the one that stops the rust streaks. Duplex 2205 and 2507 come out for hot chloride, higher differential pressure, or long service life offshore. Titanium Gr2 is for hypochlorite, seawater and chemical streams where nothing else survives long enough to be worth installing.

The Mistake We See Most Often

Buyers usually size the slot to the particle and stop there. In practice, the slot and the cut point are not the same number. A screen with a 200 micron slot does not pass everything below 200 and hold everything above it — the profile angle, the flow direction and the way material builds up on the surface all move the real cut.

So oversizing the slot to fix slow flow tends to cost carryover instead, and then you are buying a second stage you did not plan for. Tell us the duty and the target cut and we will propose slot and profile together, rather than quoting the number off a drawing that was set by guesswork.

What to Send for a Screen Quote

• Slot size, and the tolerance you inspect it to.
• Profile drawing, or let us propose one for the duty.
• Support rod spacing and rod diameter.
• Screen diameter and length, cylinder or flat panel.
• What is being filtered, and at what temperature.
• Pressure drop and backwash method.
• Material, or the environment so we can recommend one.

With that we can quote a profile, and standard sections run 20 working days from drawing approval. Look at the V-profile wire and triangular wire pages for the sections we run, or read how to specify a section if you are starting from a sketch. Write to us with the duty and we will answer with a recommendation, not a price list.