Water Well Screen Types Compared: Continuous Slot, Pipe-Based, Pre-Packed and Slotted Pipe
Continuous slot (Johnson-type), pipe-based, pre-packed, bridge slot, louver and slotted PVC well screens compared: open area, strength, use, limits.
By Serkan İnkaya, Mert Aytünür, Ümit Can Özer, ADEN Wedge Wire · 5 October 2026 · 14 min read
Water well screen types: the short answer
A water well screen is the filter section of the well casing column: it lets water in and keeps sand or gravel pack out. Four stainless designs cover most wells: rod-based continuous slot, pipe-based slip-on and direct-wrap, and pre-packed. Continuous slot gives the most open area, pipe-based suits long, heavy casing and screen columns, and pre-packed replaces hard-to-place gravel packs.
Recent enquiries we received for well screens asked for rod-based screens, pipe-based screens, pre-packed screens and PVC casing with stainless screen sections. The buyers knew the type they wanted by name but rarely how it compares with the others, so here they are side by side.
What does a well screen do?
Four terms decide how a screen performs.
- Slot is the gap between two neighbouring wires or the width of a cut opening. It decides which grains pass and which stay outside. In the US naming, "slot 30" means 0.030 in, which is 0.76 mm.
- Open area is the share of the screen surface that is open. More open area means water enters more easily and more slowly.
- Collapse strength is resistance to outside pressure from the formation, the gravel pack and any water level difference during installation and development.
- Tensile strength is the weight of pipe the screen can carry hanging below it.
In a continuous-slot wedge wire screen (often called a Johnson-type screen), a V-shaped wire is wound in a spiral around longitudinal support rods and welded at every crossing. The flat face of the V faces outward and the slot widens toward the inside. Flow runs outside to inside, so a grain that passes the narrowest point at the outer face does not lodge in the slot, and this is why the design resists clogging.
Well screen types compared
| Type | Construction | Typical open area | What carries the load | Typical use | Main limits |
|---|---|---|---|---|---|
| Rod-based continuous slot | V-wire wound on longitudinal rods, welded at every crossing | Above 30% in published comparisons; about 15-40% in practice, set by slot and wire width | Wire profile for collapse, rods for tension | Municipal, industrial and irrigation wells, gravel-packed or naturally developed | Carries no axial compression; collapse limited by wire size; inner surface not smooth |
| Pipe-based, slip-on | Separately wound rod-based jacket slid over a perforated base pipe and welded | Jacket high; inflow limited by the base pipe holes (one source: about 10% at most) | Base pipe | Deep wells, long columns, high axial load | Heavier; less inlet area; galvanic risk if base pipe is carbon steel |
| Pipe-based, direct-wrap | Wire wound directly onto the perforated base pipe | Same as slip-on | Base pipe | Very high collapse loads (catalogues recommend it above about 100 bar) | Same as slip-on |
| Pre-packed (double screen) | Inner and outer continuous-slot screens with the same slot; annulus filled with ceramic or glass beads | Per screen similar to rod-based (catalogue: about 7-15% at 0.3 mm slot, up to 48% at 1.26 mm on the inner screen) | Two screens plus packed media | Small boreholes, places where a gravel pack is hard to place | Heavier; larger outside diameter for the same bore; fixed media thickness |
| Bridge slot | Sheet punched in a press, rolled and seam welded, usually in short sections | Usually under 10% | Pipe wall | Low-cost steel wells, common in some public tenders | Low open area; low collapse |
| Louver (shutter) | Louvred openings formed in the pipe wall | Usually under 8%; practical minimum slot about 1.0 mm (0.040 in) | Pipe wall | Gravel-packed wells with a coarse pack | Low open area; coarse minimum slot |
| Mill-slot | Slots cut into pipe by saw or torch | Usually under 4% | Pipe wall | Where low cost matters more than inflow | Very low open area |
| Slotted PVC / PVC continuous slot | Plastic pipe with sawn slots, or plastic continuous slot | Slotted 4-28% (0.30-3.00 mm slot); continuous slot 6-50% (0.30-4.00 mm) | Pipe wall | Shallow, rural and community wells | Slotted pipe sits at the low end of open area |
A caution on the open area figures: the comparison for the steel types comes from a 2023 Water Well Journal article written by an engineer of a continuous-slot screen maker, and the PVC bands come from one PVC screen catalogue. They are good for ranking the types, not for calculating a well. Claims you may see that continuous slot gives "three times" or "nine times" the flow of other types are marketing figures, and we do not repeat them.
Rod-based continuous slot screens
This is the standard stainless water well screen and the type most wells use. The wire profile decides the collapse strength. A wider and taller wire resists more outside pressure. The rods decide tensile strength: the rod count, rod size and the yield strength of the steel give the load the screen can carry. The common design basis is tensile strength at yield of at least twice the hanging load, and one technical report on stainless screens suggests two to three times for rod-based screens, because end fittings are welded to the rods by hand.
A rod-based screen does not carry axial compression. The column of casing and screens is lowered and held hanging from the surface, never stood on the bottom of the hole.
Open area depends on slot width and wire width. The formula is open area % = slot x 100 / (slot + wire top width). For our standard wire profiles:
| Slot (mm) | AW28 (2.2 mm wire) | AW34 (2.8 mm wire) | AW42 (3.4 mm wire) |
|---|---|---|---|
| 0.50 | 18.5% | 15.2% | 12.8% |
| 1.00 | 31.2% | 26.3% | 22.7% |
| 1.50 | 40.5% | 34.9% | 30.6% |
Deeper wells need a heavier wire, and a heavier wire means less open area at the same slot. These are gross values. Slots in contact with a gravel pack are always partly covered by grains, so the open area in the well is lower than the table. Use them to compare screens; they do not guarantee a flow. More on wire shapes in V-wire profile performance and on the formula in open area explained, or try the open area calculator.
Pipe-based screens: slip-on and direct-wrap
A pipe-based screen puts a wire-wrapped jacket over a perforated base pipe. The base pipe is stainless steel or API 5CT carbon steel casing, drilled and deburred before the jacket goes on. On a slip-on screen the jacket is wound separately and welded to the pipe; its rods lead the water along to the nearest hole. On a direct-wrap screen the wire is wound straight onto the pipe and grips it along the full length.
Choose pipe-based when the casing and screen column is long and heavy, or when the expected collapse load is beyond what a rod-based screen of reasonable wire size can take. The base pipe carries the load, so the jacket can use a thinner wire and keep more open area.
What you give up is inflow, because water still has to pass the holes in the base pipe. One industry source puts the open area of the inner pipe at about 10% at most. When the base pipe is carbon steel and the jacket stainless, two metals touch in wet ground, so galvanic corrosion has to be addressed in the design. Our coming article on pipe-based screens on API casing covers base pipe grades, hole patterns and connections.
Pre-packed screens
A pre-packed screen is two continuous-slot screens, one inside the other, with the same slot on both. The annulus between them is filled with sized ceramic or glass beads, vibrated in place with the screen upright, and closed with welded end plates. In common catalogue sizes the packed layer is about 25-27 mm thick.
It replaces a gravel pack placed from the surface. That helps where the borehole is small, where the formation is fine, or where placing gravel evenly down a deep or narrow annulus is unreliable. Catalogues also note higher collapse resistance than a single rod-based screen and shorter drilling and development time. The cost is weight and a larger outside diameter for the same inside diameter. A dedicated article on pre-packed screens for water, drainage and remediation wells follows in this series.
Slotted pipe, bridge slot and louver screens
Bridge slot screens are cheap and common in public steel well programmes, and PVC dominates shallow rural and community wells, where cost decides.
A louver screen manufacturer's well design guide states the case against wire-wrapped screens, and it is worth knowing before a client raises it:
- Wire-wrap has the highest open area but usually costs more, and in that guide's view does not always produce more water.
- Its collapse strength is usually lower than that of the casing.
- The inner surface is not smooth because of the rods, so development with a tight swab is harder.
- Repair is harder.
- In carbon steel versions the surface exposed to corrosion is about three times that of other types.
Our view: the open area gap is real, and it matters most in fine formations where the slot has to be small. A louver screen is not practical below a slot of about 1.0 mm, so a formation that needs a 0.5 mm slot rules it out. The collapse point also stands, which is why deep wells use a heavier wire or a pipe-based screen. Swab development needs care with any screen of this type. See also wedge wire vs alternatives.
Materials in brief
Stainless water well screens are usually 304 or 304L, 316L, or duplex 2205. Guidance from the Nickel Institute for neutral pH water at ambient temperature puts the chloride limit at about 200 ppm for 304, 1,000 ppm for 316 and 3,600 ppm for 2205. Our starting rule is 316L above 200 ppm chloride and duplex above 1,000 ppm, then a check of pH, H2S, dissolved oxygen and CO2 in the water analysis. Stainless steel resists corrosion through its passive film, so we pickle and passivate every screen after welding. See material grade comparison and pickling and passivation explained.
How to choose a well screen type
- Setting depth and collapse load. Shallow and medium wells usually take a rod-based screen. As depth grows, the wire gets heavier. When the required collapse resistance or column weight goes beyond a practical wire size, move to pipe-based. German practice uses at least 0.07 bar per metre of setting depth as a rough first figure; it is not a structural proof. The highest loads often come during gravel placement and development.
- Tensile load. Add up the screen and all blank pipe hanging below it. Tensile strength at yield should be at least twice that weight.
- Formation. Get a sieve analysis. A common rule of thumb says that if at least 60% of the formation is finer than 0.75 mm, a filter pack is needed. If a gravel pack is needed but hard to place, consider pre-packed. Slot sizing from the sieve curve is covered in our slot and gravel pack article.
- Water chemistry. Chloride, pH, H2S, CO2 and dissolved oxygen decide the grade (304L, 316L or duplex) and whether carbon steel parts need isolation from stainless.
- Borehole and pump size. The pump chamber casing should be at least 2 in larger than the pump bowls. Inside the screen, upflow velocity is normally kept at or below 1.5 m/s, which sets the minimum screen diameter.
- Open area and length. Many designers still use a slot entrance velocity of about 3 cm/s, although AWWA A100 has not required a maximum entrance velocity since its 2006 edition. Open area, screen length and diameter together set the inflow.
- Logistics and budget. A 6 m screen does not fit a 20 ft container, whose inside length is 5.898 m; crated pieces should be 5.7 m or shorter, or go in a 40 ft container. On a low budget for a shallow well, PVC or bridge slot may be enough.
Standards to name in a specification
For stainless continuous-slot well screens the current German standard is DIN 4900-2:2017. DIN 4935, still quoted in older specifications, was withdrawn and replaced by it. In the US, AWWA A100 and ANSI/NGWA-01 cover well construction, and ASTM A580 covers stainless wire. Material certificates to EN 10204 3.1 are normal for export orders.
How we build well screens
ADEN Wedge Wire is a wedge wire screen manufacturer based in Istanbul, Turkey, with a European office in Sindelfingen, Germany. We wind V-wire continuously around the support rods and resistance weld every wire-rod crossing. Every screen is pickled and passivated, material certificates to EN 10204 3.1 come with the order, and we accept third-party inspection. Rod-based screens are our base design. Pipe-based and pre-packed screens are built to the project design. We work from your depth, sieve analysis and water analysis; collapse and tensile checks are a project-specific calculation on request. Product range: water well screen. For oil, gas and geothermal completions see sand control screen.
Send us your well data
Send us your borehole depth, casing size and sieve analysis (or the slot you use today), plus a water analysis if you have one. We reply within 24 hours and follow up with a screen proposal and drawing. Use the RFQ form or reply to this article by email.
Johnson Screens is a trademark of its owner. ADEN Wedge Wire is not affiliated with Johnson Screens. The term "Johnson-type" is used here only to describe a screen design.
Frequently asked questions
What is the difference between a continuous slot screen and slotted pipe?
A continuous slot screen is a V-wire wound in a spiral around support rods, so the slot runs unbroken around the screen and widens inward. Slotted pipe is a pipe with cut openings separated by solid wall. Published comparisons give continuous slot above 30% open area and mill-slotted pipe under 4%, with slotted PVC at 4-28% depending on slot width.
Is a wire-wrapped screen the same as a Johnson screen?
In everyday industry use, yes. "Johnson screen" or "Johnson-type screen" is the common name for a continuous-slot, V-wire, rod-based well screen, after the company that introduced the design. Wire-wrapped, continuous slot and V-wire screen describe the same construction. Johnson Screens is a trademark of its owner.
When do I need a pipe-based screen instead of a rod-based one?
Use pipe-based when the hanging casing and screen column is long and heavy, or when the collapse load is higher than a rod-based screen with a practical wire size can carry. Industry catalogues recommend the direct-wrap version for very high collapse requirements, above about 100 bar. The base pipe holes also limit inflow.
Can a stainless screen be used with PVC casing?
Yes. Stainless screens are joined to PVC casing with adapters. In Europe the PVC well casing thread is to DIN 4925; in the US and in parts of Africa a flush thread to ASTM F480 is common. Tell us the casing standard and size and we match the screen ends.
What open area does a continuous slot screen have?
It depends on slot and wire width: open area % = slot x 100 / (slot + wire width). With a 2.2 mm wire, a 1.0 mm slot gives 31.2%; with a 3.4 mm wire for deeper wells, 22.7%. These are gross figures. A gravel pack partly covers the slots, so the open area in service is lower.
Which stainless grade should I choose?
304L for low-chloride, near-neutral water; 316L above about 200 ppm chloride; duplex 2205 above about 1,000 ppm or in brackish and coastal wells. H2S, low pH and high CO2 also push toward a higher grade.
References
- Well Screens (2023), Water Well Journal
- Chloride guidance for stainless steels, Nickel Institute
- AWWA A100, Water Wells, American Water Works Association
- DIN 4900-2:2017, Brunnenfilter aus nichtrostendem Stahl, DIN
- ISO 668, Series 1 freight containers, ISO