The flexible connector between your separator's spouts and the plant's fixed ductwork is one of the cheapest parts on the machine and one of the few checked daily in the OEM manual. It has two jobs: let the separator move freely, and keep product off your floor. Get its length wrong and it fails at both. You can order replacement connectors and boots here or have one built to your dimensions — but read the length rule first.
On a round vibratory separator — Sweco, Kason, Midwestern, Russell Finex, and the rest — the machine is supposed to move. The springs underneath it isolate that motion from the floor. The flexible connector at each inlet and discharge spout is what lets the machine keep moving while it's bolted into a plant full of pipe that doesn't move at all. That's a harder job than it looks, and it's why a cheap rubber sleeve shows up on the same daily checklist as the amplitude reading.
Need one now? Standard corrugated connector boots (4"–10" ID, from about $49) and cut-to-length tubing in five materials are available to order online for any machine we support, and in-stock sizes ship ASAP — usually same or next business day. Odd diameter, tapered, or extra-long? We build custom connectors to your dimensions in rubber-coated nylon — any diameter, any length, tapered if you need it, stainless clamps included, typically 3–5 business days with rush jobs available.
Don't forget the clamps. Stock boots ship without them, and Sweco calls for two or three bands per connection point — so add quick-release connector boot clamps to the order. Call 866-265-1575 for other materials, a firm ship date, and rush options; the most common sizes build fast.
What a Flex Connector Actually Does — and What It Doesn't
1. Don't restrain the machine. This is the one the OEM leads with. Sweco's installation instructions for its Low Profile round separators state that connectors between inlet and outlet spouts and material conveyors must be flexible so as not to hinder the action of the separator, warning that failure to comply can damage the connectors or the material being processed. Kason and Russell Finex describe the same arrangement.
2. Contain the product. Sweco's own global marketing manager, writing in Powder & Bulk Solids, puts it plainly: cracked or torn spout connectors can cause major losses of material, allowing it into the manufacturing environment. On a food, pharma, or fine-powder line, that second clause is the expensive one.
Here's a distinction worth drawing on a flex connector: it is not primarily a vibration damper. The OEM installation instructions don't ask this part to absorb energy — they ask it not to hinder the machine's action. It's a motion accommodator; some suppliers do market convoluted flexibles on their vibration-absorbing qualities, but that's a bonus, not the job. If your connector is stiff enough to meaningfully resist the motion, it's the wrong connector or the wrong installation. (For the parts that actually do the isolating, see coil springs vs. rubber mounts and the vibration isolation glossary entry. For where the connector sits among the other wear parts, see the anatomy of a round vibratory separator.)
How much motion does it have to absorb? Less than you'd think — Sweco's Low Profile manual caps amplitude at 1/4" at 1200 RPM, down to 1/8" at 1800 RPM. A correctly sized connector is never short of travel for that. Connectors fail from how they were installed and how long they've been on, not from the amount of movement they follow.
The Length Rule: 1.5 × Spout Diameter
Sweco's installation step for connectors on its Low Profile separators gives four rules in one paragraph, and they're worth following:
- Length ≈ 1.5 × the diameter of the inlet or outlet — stated as a guideline. A 6" spout points to roughly 9"; an 8" spout roughly 12".
- Not compressed. Don't squeeze it in to close a gap that's too short.
- Installed vertical. Not cocked at an angle to reach a misaligned pipe.
- Avoid over-stretching. A connector is never installed under tension.
That last pair is where the classic field error lives. A tech looking at a floppy sleeve thinks "let me snug that up" — and installs a part that now fights the machine on every cycle. The reasoning carries to any round separator: the connector should hang straight and slack, neither taut nor squashed. Too long is a real failure too, just a slower one — excess length folds, and the fold line is where abrasion and cracking start.
Treat 1.5× as a starting point, not a tolerance. Sweco's own spare-parts list spans a wide band around it — from a 3" connector 8" long (2.7× diameter) to a 10" connector just 10.5" long (about 1×). The real constraint is your machine's actual spout-to-spout gap plus enough overlap to clamp at each end; the 1.5× guideline is the sanity check on it.
In practice, stock corrugated boots come in 4", 6", 8", and 10" IDs — all four in a 10.75" length, with a 12" length stocked in 6" and 8". Most installations land on one of them. If your gap doesn't, that's the case for a made-to-length connector rather than forcing the wrong one into place.
How Connectors Actually Fail
Five signatures, all findable in about thirty seconds with a flashlight:
| What you see | What it means |
|---|---|
| Dry, hard, chalky rubber; fine surface cracking | Age embrittlement. Rubber dries out, gets brittle, and cracks. Ozone and sunlight accelerate it — natural rubber and nitrile are the most vulnerable; EPDM, silicone, and neoprene hold up better. |
| Thin or worn-through spot on the inside, usually low | Abrasion. Product runs through this part continuously and the wear can be severe — worst with sharp or dense material. |
| A crack following a fold or crease line | Flex fatigue, usually from a connector that's too long and folding. The connector flexes continuously; a permanent crease concentrates every cycle in one line. |
| A tear at the clamped end, or the sleeve pulled off | Too short, over-stretched, or misaligned. Often shows up at start-up or shutdown, when movement is greater than during steady running. |
| Dust film on the floor or frame under a joint | Loose clamp or a pinhole. Clamps loosening under vibration is expected, not exceptional — it's on the daily checklist for that reason. |
Check It Daily. Change It on a Schedule.
Spout connectors appear on the daily maintenance table in Sweco's Low Profile separator manual — check for holes, cracks, or damage, and check that connectors are properly fastened at the connection point. They're also on its pre-start-up checklist. Not weekly. Not "when it leaks." Most plant screener maintenance schedules leave connectors off entirely; they belong on yours.
And there's a published number most people have never seen: for that same Low Profile line under normal usage, Sweco estimates connector life at about six months and recommends changing them at that point. Treat it as OEM guidance for normal duty, not a universal law — an abrasive mineral line will eat one faster, and a clean, cool, intermittent powder line may go considerably longer.
The way well-run plants actually handle this
Don't wait for the tear. Buy connectors two at a time and keep the spare on the shelf next to your spare screen. Then change them on your own schedule — during a planned shutdown you already have, with the machine already open and cool — instead of at 2 a.m. with product on the floor. A connector is a five-minute change with the right part in hand and an hour of scrambling without it. If you're already pulling the machine down, that's also the moment to inspect the screen and get worn ones out to be rescreened so they come back as your next spare. Same discipline, two parts, one shutdown.
Clamping It Right
Before your hands go anywhere near a spout: lock out the machine against accidental start-up. Changing a connector is a five-minute job that puts you in contact with parts that move — see our vibratory screening safety guide.
Sweco's instruction for its Low Profile machines is to fasten each connector with two or three heavy-duty clamp bands per connection point — not one, and stock boots don't come with any, so order clamps alongside the part. Beyond that, three things matter:
Don't crank it. Clamp makers publish real limits — Ideal-Tridon gives roughly 35 lbf-in installation torque for its standard worm-gear series against a published minimum destructive torque on the order of 60 lbf-in, and warns that overtightening damages the hose and decreases clamping efficiency. Tight enough to seal, not tight enough to cut.
"Stainless" clamps often aren't, entirely. A very common configuration pairs a stainless band with a plated carbon steel screw. On a washdown line or anywhere with chlorides, that screw is the part that rusts and seizes — and all-stainless versions are separate part numbers, so specify them. Clamp makers' own corrosion-class tables put food processing in the all-316 class, not the plated-screw class. (Same logic as 304 vs. 316 for the screen itself: 304 standard, 316 for sanitary and corrosive duty.)
Make it easy to remove. Sweco's cleaning procedure specifically recommends easily removable fastening devices, because the connector has to come off to be cleaned properly. If your clamps are a fight, cleaning gets skipped — which is the argument for quick-release clamps on any connector that comes off for washdown.
Picking the Material
There's no single best material — there's a best material for your product, temperature, and washdown routine. This is connector material selection; deck and ring gaskets are a separate decision, driven by compression set rather than flex life. Here's the honest short version, with the full side-by-side across all nine options on our connector material grading chart:
| Material | Pick it when |
|---|---|
| Natural / gum rubber | Abrasive product, ambient temperature. Top-tier abrasion and tear resistance, low cost. Poor in sunlight and ozone; not a high-heat material. |
| Neoprene | A good all-rounder — solid abrasion, better weather and ozone resistance than natural rubber or nitrile. |
| EPDM | Outdoor installations and higher temperatures. Excellent weather and ozone resistance. Not for oils. |
| Silicone | Hot product and food contact — the widest temperature range of the group. But it rates weakest on tear and among the weakest on abrasion. A heat and food-contact choice, not a wear choice. |
| Clear flex polyurethane | When you want to see flow, plus excellent abrasion resistance and the easiest cleaning in the lineup. A common choice on powder lines. |
| Rubber-coated nylon (RCN) | The workhorse sleeve — a soft rubber coating on a fabric backing, with the reinforcement carrying the load. Our custom connectors are built from it. |
| Wire-reinforced polyurethane | Where vacuum or negative pressure would collapse a plain sleeve, or on long runs. Abrasion resistance plus collapse resistance. |
One caution on temperature ratings. Published figures are usually maximums, not continuous service ratings — the same material can be listed 100 °F apart by two reputable sources. If you're running near a limit, ask us for the specific compound's datasheet. And heat accelerates the aging that eventually cracks any elastomer, so temperature isn't the only clock.
Material certifications and a Certificate of Conformance are available on request, so your QA file has the actual compound documented rather than a field guess.
Food, Pharma, and the Sanitary Question Nobody Answers Straight
Say "compliant," not "approved." The primary regulation governing rubber parts in repeated food contact is 21 CFR 177.2600, and it's permissive, not a certification scheme: it says such articles "may be safely used" in food processing subject to its provisions, enumerating permitted ingredients and setting extractives limits. There is no FDA registration or approval of a rubber connector. The correct phrasing on a spec sheet is conforms to 21 CFR 177.2600. (More in our FDA compliance glossary entry.) PTFE is covered by a different section entirely — 21 CFR 177.1550, perfluorocarbon resins — which permits only specified optional adjuvant substances, each required to comply with applicable food-additive regulations. Virgin unfilled PTFE is the clean case; a filled grade needs every filler documented as compliant.
Don't expect a 3-A symbol on a clamped sleeve. No 3-A standard covers the flexible connector assembly on a dry-bulk separator: the hose assembly standard is scoped to liquid and, per published summaries, excludes band- and worm-gear-clamped fittings along with corrugated inner surfaces. Two things do apply — 3-A covers the machine itself, and its multiple-use rubber materials standard (18-03) can apply to the compound your connector is made from. That distinction is the whole answer: you document the material, you don't certify the assembly.
So the sanitary burden on this part is carried by material compliance and cleaning practice rather than by a symbol — which for your QA file means the compound datasheet and Certificate of Conformance. The OEM cleaning guidance is easy to follow: clean connectors along with the sifter and examine them for holes and cracks while they're off, prefer dry cleaning to wet, and prefer vacuum to brushing or compressed air — blowing dust down just relocates it into the rest of the plant. If connectors stay in place through a CIP cycle, pull and wipe them afterward so cleaning chemistry doesn't sit on the elastomer.
Measuring for a Replacement
Five things get you the right part:
- Spout outside diameter (OD) — measured in several places, and use the largest reading, since the sleeve has to clear the widest point. Out-of-round spouts are common, and one measurement will lie to you. Your spout OD is the sleeve ID you order.
- Overall length — the connector's own length, in the neighborhood of 1.5 × the spout diameter. Measure your spout-to-spout gap first, then add the overlap that sits on each spout. Order to the gap alone and you'll get a part with nothing left to clamp. Shortcut: if you still have the old connector, the clean band where it sat on the spout is your overlap — measure it. If it's gone, call us with the gap and the spout OD and we'll do the math.
- Material — from the table above. Check availability in your diameter while you're there: the common materials run 4"–14", but silicone and wire-reinforced polyurethane are stocked in fewer sizes and anything else is a quick phone call.
- Style — corrugated boot, straight tubing, or wire-reinforced.
- Same or different diameters at each end — tapered transitions are available on custom builds.
The fit itself is governed by how much the sleeve has to stretch over the spout:
% stretch = (spout OD − sleeve ID) ÷ sleeve ID × 100
Our sizing guide for rubber-coated nylon gives the working ranges for that reinforced material: 0–2% installs easily with a clamp; 2–4% is usually workable with a little warmth and a slip aid; 4% and up gets difficult, and past about 5% you risk tearing or delaminating the sleeve. Reinforced fabric sleeves stretch far less than bare rubber sheet — the reinforcement is doing its job — so don't assume a rubber elongation figure applies to a reinforced connector. And if you'll be pulling the connector off often for cleaning, a slightly larger ID that relies on the clamp will outlast one you have to fight onto the spout every time.
Not sure what you've got? Send us photos first — a picture of the connector in place, one of the spout, and your two diameters is usually all we need to identify it. If the photos aren't conclusive, then ship us the old one and we'll match it. Everything is built to fit your machine, or we make it right.
The Bottom Line
Three things fix almost every connector problem: install it relaxed, vertical, and roughly 1.5 × the spout diameter in overall length; use two or three clamp bands and don't overtighten them; and put it on a replacement schedule instead of waiting for the tear.
Ready to order? Browse connectors, boots, and cut-to-length tubing, or get a custom connector built to your dimensions — any diameter, any length, tapered if you need it, stainless clamps included, with other materials available by phone. Material certs and a Certificate of Conformance are available on request for your QA file. Built to fit your machine, or we make it right. Call 866-265-1575 or request a quote for a firm ship date and rush options — the most common sizes build fast, and buying the spare now is a lot cheaper than needing it later.
Frequently Asked Questions
How long should a flex connector be on a round vibratory separator?
Sweco's published guideline for its Low Profile round separators is approximately 1.5 times the diameter of the inlet or outlet spout — so roughly 9" for a 6" spout and 12" for an 8" spout. Treat it as a starting point rather than a tolerance: Sweco's own connector part numbers range from about 1× to 2.7× diameter. What governs is your actual spout-to-spout gap plus enough overlap to clamp at each end. However it works out, it should hang vertical and relaxed — not compressed to fit a short gap, and never stretched.
How often should separator connectors be replaced?
Inspect them daily for holes, cracks, and loose clamps — that's where they sit on Sweco's Low Profile maintenance table. For replacement, Sweco estimates roughly a six-month life under normal usage on that same line. Abrasive or hot service shortens that; clean, cool, intermittent duty can extend it. The practical answer is to keep a spare and change it during planned downtime.
Can a flex connector be installed stretched tight?
No. The published instruction is explicit: connectors should not be compressed, and over-stretching should be avoided. A taut connector restrains the separator's motion — the opposite of its job — and tends to tear at the clamped end during start-up and shutdown, when movement is greatest.
What material should I use for a food or pharmaceutical line?
Silicone, clear polyurethane, white gum rubber, and EPDM are all offered in compounds that conform to 21 CFR 177.2600 for repeated food contact. Choose between them on temperature, abrasion, and cleanability rather than on compliance alone — silicone for heat, polyurethane for abrasion and easy cleaning, EPDM for steam and hot water. Ask for the datasheet and Certificate of Conformance for the specific compound.
Are separator flex connectors 3-A certified?
A clamp-and-sleeve connector generally isn't, and no 3-A standard specifically covers flexible connectors on dry-bulk separators. The hose assembly standard is written for liquid hose and excludes band-, strap-, and worm-gear-clamped fittings along with corrugated inner surfaces. A separate sanitary fittings standard exists that some specialized connector designs are certified against, but that's a different connection style. The machine itself is often built to 3-A; on the connector, sanitary performance comes from material compliance and cleaning practice.
How do I measure for a replacement connector?
Measure the spout outside diameter in several places (out-of-round spouts are common), then measure the spout-to-spout gap and add the overlap you need to clamp at each end — that total is the connector's overall length, not the gap alone. Compare the spout OD to the sleeve ID: on reinforced rubber-coated nylon, 0–2% stretch installs easily, 2–4% is workable with warmth and a slip aid, and past about 5% you risk tearing. Send us photos of the connector and spout with those measurements and we'll identify it for you.
