Y‑strainers, 1/4" to 4"

A Y‑strainer is a tee with a screen in the leg. Flow enters, passes through a perforated or woven mesh element angled down into the branch, and leaves clean. Anything larger than the mesh opening stays behind in the leg. Because the leg points downward in service, gravity keeps the debris where the screen already put it, and a cap at the bottom lets you flush or lift it out.

What it catches is rarely the fluid’s fault. It is construction debris — weld spatter, pipe scale, rust, thread cuttings, jointing compound, the odd offcut. A new system sheds all of it in the first weeks of running, and it all arrives at whatever is narrowest downstream. That is usually a globe valve seat, a control valve trim, a flow meter, a pump impeller or a regulator — parts that cost far more than the strainer and take far longer to replace.

• It protects, it does not isolate. A Y‑strainer has no closure member and no handle. Put a gate valve or a ball valve either side of it so you can take it out of service to clean the screen without draining the line.
• The mesh is a trade, not a setting. A finer screen catches more and blocks sooner, and pressure drop rises as it fills. Choosing mesh is choosing how often someone goes and cleans it. The chart, and how to read it.
• The screen is the wear part. Everything else is a casting. Screens are SS316 on the stainless variants and SS304 on the cast steel ones — the part‑by‑part comparison.
• Pressure drop is the instrument. A clean strainer costs you very little. A blocked one costs you a great deal, and the only way to know which you have is to watch the differential. How to monitor it.
• Five variants, one screen principle. The manufacturer’s catalogue is the reference for every figure below; anything it does not state — a dimension, a mesh size, a temperature — we obtain from the factory or measure on a stocked unit. The comparison.

Five variants, one photograph each. All photographs of the stocked item, not renders.

• JIS 10K cast steel dimensions are quoted per order. The catalogue publishes the part numbers for this variant but not a dimension table, so we quote dimensions against your enquiry instead — ask us for any figure and we will measure a stocked unit. The JIS 10K SS316 table is complete if you want a guide to JIS flange dimensions at these sizes.
• ANSI 150 cast steel part numbers are quoted as per the catalogue. The rows from 1" to 2½" read VL‑CS‑YS‑F‑10K‑nn and the 3" and 4" rows read ‑150‑; the dimensions are ASME B16.5 Class 150 throughout, so the fit is ANSI. State the size and flange standard on your order and we match the code for you.
• Temperature ratings are as the catalogue states them: −20 to 230 °C for the stainless variants and −29 to 150 °C for cast steel, both with a PTFE gasket. If your duty runs above 150 °C, choose a stainless variant.
• The threaded variant runs 1/4" to 4" (DN8 to DN100) — the dimension table carries full rows with part numbers from 1/4" up, and 1/4" through 1¼" are available in both thread forms. No working temperature is published for it; we obtain one from the factory on request.
• ANSI 150 and JIS 10K do not bolt to one another. Both sit near 1.6 to 2 MPa, which is what makes it an expensive mistake rather than an obvious one. Check the bolt circle on the mating flange, not the pressure rating.
• The flanged variants stop at 4" and the threaded one starts at 1/4". Between them they cover DN8 to DN100 with no gap, and 1½" to 4" is available in either style.

• Read it downwards for finer. Mesh number rises, opening falls, filtration improves and pressure drop rises. There is no free end of this table.
• The millimetre column is ours. The manufacturer publishes microns and inches; we have added millimetres because that is what the screens are specified in — the standard 1 mm element is exactly 18 mesh.
• “Typically catches” is guidance, not a specification. What a screen actually stops depends on particle shape as much as size — a long thin sliver can pass a hole it is much larger than. Size the screen from the smallest clearance you are protecting.
• Every micron figure here is the standard sieve value for that mesh, and every inch figure is that micron figure divided by 25,400. We re‑checked all seventeen rows and changed none of them — only the explanation above needed fixing.

A Y‑strainer has no moving parts. There is a body, a screen, a cover or cap, a gasket and the bolting that holds the cover on. That is the whole machine, and it is why a strainer outlasts everything it protects — provided somebody empties it.

• The screen grade differs from the body grade on the cast steel variants. A WCB body with an SS304 screen is the normal, sensible arrangement — the screen is thin and needs corrosion resistance the body does not. But note it is 304, not 316: on chloride‑bearing service the screen will pit before the body does.
• ⚠ The cast steel variants do not publish a mesh size. The stainless pair state SS316 1 mm mesh; the cast steel pages say only “filter screen, SS304”. Specify the mesh you want when you order a cast steel strainer rather than assuming 1 mm. The chart.
• The bolting is the real material difference. A193 B7 / A194 2H on cast steel is stronger alloy‑steel pressure bolting; SS304 on the stainless variants is more corrosion‑resistant and weaker. Each suits its body.
• PTFE gasket on all five. Which is what makes the 150 °C ceiling on the cast steel variants hard to explain — the stainless ones use the same gasket and are rated to 230 °C. The published figures.
• Screens are a spare part, not a fixture. They are the only thing that wears or blocks, they lift out through the cover, and we stock them. Send the size, the variant and the mesh.

There is no fixed service interval for a strainer, and any supplier who gives you one is guessing. The interval depends entirely on how dirty your fluid is, and the only honest way to set it is to measure. That is what the two gauges are for.

• Record the pressure drop when it is clean. Fit a gauge at the inlet and one at the outlet, and note the difference on a new screen. That baseline is the number everything else is judged against — without it, a later reading tells you nothing.
• Watch the differential, then set your interval from it. As the screen fills, drop rises. Check and log it often at first — especially in the first weeks of a new system, when the pipework is shedding its own construction debris — and let the pattern tell you the interval.
• Flush the bottom cap first. Small amounts of contamination clear by opening the cap and letting flow carry the debris out. That is a minutes job and needs no dismantling.
• If flushing is not enough, lift the screen out. Remove the bottom cover and take the element out. It is self‑aligning, so it goes back the way it came. Clean it, check it for damage, and replace it if it is torn or deformed — a holed screen filters nothing and gives no warning that it has stopped.
• ⚠ A blocked screen can collapse. The differential across a fully blocked element can exceed what the mesh will take, and once it tears the debris goes straight downstream. This is the real failure mode of a strainer, and it happens far below the body’s pressure rating.
• Rising drop with a clean screen means something else. If the differential climbs and the element is clear, look downstream — a partly closed valve or a fouled component. The strainer is doing its job and telling you about someone else’s.
• Keep a spare screen. The element is the only wear part on the whole assembly. Having one on the shelf is the difference between a clean and a shutdown.