SCREEN SPECIFICATION GUIDE
Slot Opening, Profile Wire & Open Area
Slot opening is the clear gap between adjacent profile wires. Theoretical surface open area is the slot width divided by the repeating pitch: open area (%) = slot ÷ (slot + wire surface width) × 100. This geometric ratio excludes frames, supports, blocked areas and fouling; it does not predict flow capacity by itself.
Clear opening, wire width and pitch
Measure slot and wire width at the screening surface, in the same direction and units. For a regular parallel-wire surface, one repeat consists of one clear slot plus one wire surface width. Profile depth and support rods are separate dimensions.
| Term | Meaning | Unit used here |
|---|---|---|
| s — slot opening | Clear gap between adjacent wires at the screening face | mm |
| w — wire surface width | Width occupied by one wire at the screening face | mm |
| p — pitch | One repeat: w + s | mm |
| OA — theoretical open area | Open fraction of the regular screening surface × 100 | % |
A worked geometry example
Consider a hypothetical flat screening surface with a uniform 0.50 mm slot and 1.50 mm wire surface width. These are illustrative inputs, not a Wedge Wire Works stock size or tolerance commitment.
Pitch = 0.50 + 1.50 = 2.00 mm
Open area = 0.50 ÷ 2.00 × 100 = 25.0%
If the slot remains 0.50 mm but wire width is 1.00 mm, the calculated open area is 0.50 ÷ 1.50 × 100 = 33.3%, rounded to one decimal place. The calculation does not establish which profile is suitable for the load.
| Illustrative slot (mm) | Wire surface width (mm) | Pitch (mm) | Theoretical open area |
|---|---|---|---|
| 0.50 | 1.50 | 2.00 | 25.0% |
| 0.50 | 1.00 | 1.50 | 33.3% |
Why equal slots do not mean equal screens
A wider wire occupies more of each repeat. A different wire depth or support arrangement also changes construction without being captured by the surface open-area percentage. Compare the full screen specification: slot, wire profile, support geometry, material and operating duty.
Gross area, effective area and flow
For a uniform, unobstructed flat screening surface, multiplying its gross area by the theoretical open fraction gives a geometric opening area. Real assemblies require further accounting for frames, supports, solid end sections and blocked or fouled zones. Avoid subtracting overlapping obstructions twice.
For cylinders, distinguish active screen length from overall length including fittings. For water intake projects, use the project’s defined velocity and effective-area basis. More theoretical open area does not automatically produce the same percentage increase in usable flow: pressure loss, fluid properties, solids, fouling and the system arrangement also matter.
How to use this when requesting a quote
Provide the required slot and any prescribed wire profile, plus the active dimensions, medium, flow and pressure conditions. Ask for the proposed profile and support design to be identified. Do not select the thinnest wire only to maximize this ratio.
Calculation basis and reference
The formula above is derived from the repeating geometry of parallel slots and wires. It assumes a uniform clear slot and wire width measured at the same screening surface. Rounded results describe the example geometry only.
Johnson Screens’ screen flow calculator provides further manufacturer context on wire width, slot size, active length and intake calculations. Its assumptions, including no blockage, should be read before using its outputs. It is an independent technical reference, not a KUNYU performance guarantee.