Most people start with volume, because it is the figure in the product name and the easiest to compare. It is also the one that most often turns out not to be the constraint.
Usable volume tells you how much mixture goes in.
Key points at a glance
Working load tells you how much you may lift afterwards. With mineral sludges this is nearly always the real limit. A bag can be geometrically half full and…
Two readings of that table are worth spelling out. XL and XXL occupy exactly the same square metre of floor and differ only in height, 0.80 against 1.25…
Volume decides how much goes in. Density decides what it weighs. The load rating has to match the second figure.
Three numbers decide the size, and volume is the least useful
Working load tells you how much you may lift afterwards. With mineral sludges this is nearly always the real limit. A bag can be geometrically half full and already at its rating.
Build height tells you whether the bag fits under your filling point and under your crane hook. Two of our sizes have an identical footprint and differ only here, which makes height a decision in its own right rather than a detail.
To those three, add a fourth question that costs nothing to ask and a lot to answer late: how does the filled bag leave the site? Hook height, forklift lift and the clear height of the route to the disposal point all belong in the sizing, not in the delivery week.
The six versions side by side
| Version | Usable volume | Base area | Height | Working load |
|---|---|---|---|---|
| Compact nonwoven bag | not volume rated | 1.19 × 0.55 m flat | needs a holder | none stated |
| Size M | 0.125 m³ | 0.50 × 0.50 m | 0.50 m | up to 400 kg |
| Size L | 0.5 m³ | 0.90 × 0.80 m | 0.70 m | 400 / 600 / 900 kg |
| Size XL | 0.8 m³ | 1.00 × 1.00 m | 0.80 m | 400 / 600 / 900 kg |
| Size XXL | 1.25 m³ | 1.00 × 1.00 m | 1.25 m | 400 / 600 / 900 kg |
| Custom size, low profile | not stated | 0.99 × 0.60 m | 0.40 m | up to 400 kg |
Two readings of that table are worth spelling out. XL and XXL occupy exactly the same square metre of floor and differ only in height, 0.80 against 1.25 metres, so the choice between them is about headroom rather than space. And the L, at 0.90 by 0.80 metres, is the size that fits on a Euro pallet, which is why it often wins on handling even where a larger bag would fit the quantity.
Working out the load rating from density
Volume decides how much goes in. Density decides what it weighs. The load rating has to match the second figure.
| Starting material | Approx. density after dewatering | Mass at 0.5 m³ | Mass at 0.8 m³ | Mass at 1.25 m³ |
|---|---|---|---|---|
| light organic sludges | around 0.8 t/m³ | around 400 kg | around 640 kg | around 1.000 kg |
| mixed mineral sludges | 1.0 to 1.3 t/m³ | 500 to 650 kg | 800 to 1.040 kg | 1.250 to 1,625 kg |
| heavy mineral sludges, stone, metal fines | 1.5 t/m³ and above | 750 kg and above | 1,200 kg and above | 1,875 kg and above |
These figures are orientation, not a commitment. Actual density depends on grain size, residual moisture and conditioning.
Read down the columns and the practical conclusion appears on its own: with mineral material the larger sizes cannot be filled to the top edge whatever rating you order. You are then filling to a mass, not to a line. Two things follow. Order the 900 kg rating, and mark a fill height on the bag for the people who use it. Where the calculation says you would only ever use half of an XXL, two L bags will often do the same job with less handling risk, because each one can be lifted on its own.
The fastest way to replace all of this with certainty: dewater one batch, weigh the bag, note the number, and use it for every order from then on. Half an hour of work settles the question permanently.
Sizing by application
| Situation | Sensible starting point |
|---|---|
| Occasional small batches, tight floor space | Size M, 0.125 m³ |
| Regular batches, a fixed wash-down point | Size L, 0.5 m³ |
| Larger batches, headroom limited | Size XL, 0.8 m³ |
| High quantities, floor space tight | Size XXL, 1.25 m³ |
| An existing chamber, pit or shallow tray | Custom size at 0.40 m |
| A holder is already there and only an insert is needed | Compact nonwoven bag |
How the process itself runs, and where it stops being the right method, is covered in the process guide. If you would rather have the sizing checked than work through it yourself, send us the figures.
Frequently asked questions about choosing a filter bag size
These answers provide a first guide to volume, weight and installation conditions
Which size is suitable for small sludge batches?
For small batches and limited floor space, the 0.125 m³ version is usually the most practical starting point.
Is the largest filter bag always the most economical choice?
No. A large version only pays off if the sludge quantity, working load, floor space and removal route all suit it.
Can the bag be filled completely?
Only while the permitted working load is not exceeded. With heavy sludge, the working load can be reached before the bag is full.
What is the difference between 0.8 and 1.25 m³?
Both versions have the same 1.00 × 1.00 m footprint. The 0.8 m³ version is 0.80 m high, while the 1.25 m³ version is 1.25 m high. The choice therefore depends mainly on filling height, hook height and available headroom.
When do I need a custom size?
A custom size makes sense when the standard dimensions do not fit the available footprint, build height or existing holder.
Which working load should I choose?
The working load must match the actual mass of the bag and its contents. With heavy mineral sludge, do not select on usable volume alone.
Still unsure which filter or next step fits?
Send us the medium, dimensions and application. We will help you decide whether a standard product is suitable or whether the case needs a custom solution.
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