Quick answer: flight height comes from the product, flight spacing comes from the product footprint plus the incline angle, and side guards come as part of the same order because a flight pushes product up the slope and does nothing to stop it sliding off the side. Standard flight heights are 50, 102 and 150 mm and standard side guard heights are 50, 100 and 150 mm, both in PP or PE, and both can be cut to suit.
First find the angle where your product actually slips
Before any part number, do a five minute test. Put a piece of the belt you plan to use on a board, place the product on it, and tilt the board until the product starts to slide. That angle is your limit for a plain surface, and it will surprise you how much it moves with a wet product, an oily film, or a change from carton to shrink wrap.
If your conveyor sits below that angle, you may not need flights at all, and a textured or nub top surface will do. If the conveyor is steeper, flights are the only honest answer. Do the test with product in the worst state it comes in, not with a clean dry sample.
Flight height follows the product, not the slope
Two different jobs are being confused when people ask how tall a flight should be.
If the flight only has to stop a stable item from creeping back, a low flight is enough. A carton or a case sitting on its base needs a backstop, not a wall, and a 50 mm flight does that on most packaged goods.
If the flight is carrying loose bulk material such as granules, small parts or cut vegetables, the flight is holding a pocket of product against gravity and it has to be taller than the product pile will build up. That is where 102 mm and 150 mm are used. Flights can be cut down, so if the right answer sits between two sizes, take the larger one and trim it.
| Situation | Flight height to start from | Why |
|---|---|---|
| Cartons, cases, stable packs on a mild slope | 50 mm | Only a backstop is needed, taller flights get in the way at the discharge |
| Bottles, jars, unstable single items | 50 or 102 mm | Must reach above the centre of gravity or the item tips instead of being pushed |
| Loose bulk, granules, small parts | 102 or 150 mm | The flight holds a pocket, so height sets how much each pocket carries |
| Steep lift, wet or sticky product | 150 mm | Product slumps backwards down the pocket as the angle rises |
Spacing is set by the product, then checked against the ends
Set the pitch between flights so each pocket holds one product, or one sensible batch of bulk. Measure the product along the direction of travel, add clearance so it drops in without being trapped, and round the result to a whole number of belt pitches. Flights mount on the module, so the spacing is always a multiple of the belt pitch, never an arbitrary millimetre value.
Then check both ends. At the infeed, the pocket has to be open long enough for the product to land in it at line speed. At the discharge, the flight has to release the product cleanly as it goes over the sprocket. Tight spacing plus a small sprocket often means the product is still in the pocket when the flight has already tipped over the nose, and it lands back on the belt instead of on the next machine.
Why flights and side guards get ordered together
A flight only works in the direction of travel. Tilt a belt and the product loses grip in every direction at once, so it slides backwards until the flight catches it, then it walks sideways along the face of the flight and drops off the edge. That is the failure people describe as "the flights are not working" when the real gap is the missing side guard.
Order belt flights and belt side guards on the same line, match the heights, and state the resin, because both parts touch product and belong in the same food-grade material specification as the belt. A 150 mm flight behind a 50 mm guard leaves the top of the pocket open at the sides, and on a wet product that is where you will find the spill.
The clearance at the joint
Flights and side guards must not touch. Both are mounted to the belt and both swing through an arc as the belt wraps the sprocket, and they swing on different radii. If the flight runs hard against the guard, the two parts collide at the nose and one of them breaks off, usually taking a module fixing with it.
Leave the flight short of the guard on each side. How much depends on the sprocket diameter, the guard height, and the belt series, so it is worth asking for the value for your build rather than copying it from another line. The tighter your sprocket, the bigger the gap has to be. Some spill through that gap is normal and accepted; the alternative is broken parts.
What the incline does to tension
On a flat conveyor the belt pull comes from friction alone. Put the same load on a slope and the belt now carries a share of the product weight as well, so tension rises with the angle and with the load in the pockets. Two things follow.
The drive gets bigger, and it sits at the top of the incline pulling the loaded side, not at the bottom pushing it. The belt strength figure on the series datasheet also becomes a live constraint instead of a comfortable margin, so check it against the loaded case rather than the empty one, which is what the belt pull calculation is for, since a lift enters it as a term of its own. Our belt selection guide covers how the strength rating relates to width and pull.
The return run is the second effect. A belt with tall flights on it wants to lift away from its supports on the return, and at the transition where the slope meets a horizontal section the belt tries to leave the track altogether. Pressure rollers hold it down at that point. Fit them at every transition and at any place where the return span is long enough for the belt to hang, since a return that lifts and drops turns into wear and tracking complaints that look like a belt fault.
Which series take flights, guards, or both
| Part | Standard heights | Compatible series | Material |
|---|---|---|---|
| Belt flights (cleats) | 50 / 102 / 150 mm, cut to size | 400, 900, 956, 976, 986, 1000, 5935, 7100, OPB | PP / PE |
| Belt side guards | 50 / 100 / 150 mm | OPB, 976, 986, 4809, 5935 | PP / PE |
Four series accept both parts as standard: 976, 986, 5935 and OPB. If your line needs flights and guards together, start there. The 986 flat top belt is the usual pick for packaged goods on a slope, and the OPB flat top belt suits wider frames and heavier duty. Both sit in the same family as the rest of the belt accessories, so flights, guards and rollers can go on one order.
Picking a series that takes only flights is not a mistake by itself, it just means the guard has to be a fixed rail on the frame instead of a moving guard on the belt. Fixed rails work well for firm packages and badly for anything that can wedge under the rail.
What to send with the enquiry
- Product: what it is, its size in three dimensions, its weight, wet or dry, loose or packaged.
- Incline angle, or the rise and the run if the angle is not known, and the total belt length.
- The slip angle from the tilt test described above, if you can run it.
- Belt width, line speed, and throughput in units or kilograms per hour.
- Whether the conveyor has a horizontal section at either end, which decides where hold-downs go.
- Existing belt series if this is a modification, plus a photo of the belt underside.
Send that through the contact form or on WhatsApp and we will come back with a flight height and pitch, a guard height, and the clearance figure for your sprocket.
