How to size a bag filter housing: bag size, flow, pressure and material

Bag filters are the simple way to take solids out of a liquid at high flow. A filter bag sits in a basket inside a pressure housing; the liquid passes through the bag and the solids stay inside it, so each change-out takes the dirt away with the bag. Sizing the housing comes down to five things: the bag size, the number of bags, the pressure, the temperature and the housing material.

At a glance

• Most housings take size 01 or 02 bags. A size 02 bag is twice the length of a size 01 and carries about twice the flow.

• For clean, water-like liquids allow about 20 m³/h per size 01 bag and 40 m³/h per size 02 bag. Viscous or heavily loaded liquids need more bags.

• Single-bag housings cover up to 40 m³/h; multi-bag housings with 2 to 16 bags go up to 640 m³/h.

• Stainless steel housings in the Vens range take up to 10 bar and 90 °C. Plastic housings are for corrosive liquids at lower pressure and temperature.

• A quick-opening cover saves time where bags are changed often.

Bag sizes and flow

Bag size	Nominal flow per bag	Vens housings that take it
01	20 m³/h (15 m³/h in UPVC)	EBF-0101, ETPL-0101, ESDL-0101, plastic PSDL-0101
02	40 m³/h (25 to 40 m³/h in plastic)	EBF-0102, ETPL-0102, ESDL-0102, all EMBF and FOBF multi-bag housings, plastic PTPL and PSDL-0102
03	6 m³/h	EBF-0103, ESDL-0103
04	12 m³/h	EBF-0104, ESDL-0104, PSDL-SF-0104
05	20 m³/h	PSDL-SF-0105

These flows are for clean, water-like liquids. For oils and other viscous liquids, fine ratings or heavy solids, we size the housing with more bag area.

Choosing the housing type

Series	Bags	Flow	Pressure, temperature	Connections	Choose it when
EBF, eco	1 (size 01 to 04)	6 to 40 m³/h	6 bar, 90 °C	BSP thread	Light duty and pre-filtration at low cost
ETPL, top entry	1 (size 01 or 02)	20 to 40 m³/h	10 bar, 90 °C	DN 50 flange	Even loading of the bag and a quick eye-bolt cover
ESDL, side entry	1 (size 01 to 04)	6 to 40 m³/h	10 bar, 90 °C	DN 50 flange or BSP	Bag changes without spilling unfiltered liquid
EMBF, multi bag	2 to 12	80 to 480 m³/h	10 bar, 90 °C	DN 80 to DN 250 flange	Large continuous flows
FOBF, flash open	3 to 16	80 to 640 m³/h	10 bar, 90 °C	DN 80 to DN 250 flange	Frequent change-outs and batch processes
PBF, plastic	1 (size 01 to 05)	12 to 40 m³/h	4 to 10 bar, 45 to 100 °C	DN 40 to DN 65 flange	Acids, alkalis and other corrosive liquids

Pressure, temperature and material

The stainless steel housings are rated to 10 bar (6 bar for the EBF) and 90 °C. The ETPL, ESDL, EMBF and FOBF are designed in accordance with PED and ASME. For acids, alkalis and other corrosive liquids, plastic housings avoid metal altogether:

• PP: up to 80 °C and 6 bar

• PVDF: up to 100 °C and 6 to 10 bar, depending on model

• UPVC: up to 45 °C and 4 to 7 bar

Check the bag material and the seals against the liquid as well.

Choosing the bag

• Needle felt, polypropylene or polyester: general-purpose depth filtration.

• Nylon monofilament mesh: a surface mesh for coarser ratings.

• Extended-life bags: more media in the same size, for longer runs between changes.

• Absolute-rated bags: higher efficiency at the stated rating.

• Oil-absorbing bags: take traces of oil out of water.

• Activated carbon bags: remove odour and organic compounds.

Vens bags are available in ratings from 1 to 100 µm.

When to change the bag

Fit a pressure gauge on the inlet and the outlet. As the bag fills, the difference between them rises. Change the bag at the differential pressure recommended for it, before it can burst or be bypassed. A multi-bag housing, or two housings in parallel, lets the line keep running while bags are changed.

What to send us for a quotation

• The liquid, its viscosity, temperature and pressure

• The flow rate

• The solids to remove and the rating you need

• The pipe connection size

• How often you can change bags

Frequently asked questions

How many bags do I need?

Divide the flow by the nominal flow per bag for your bag size, then allow extra for viscosity or heavy solids. For 150 m³/h of water with size 02 bags, that is four bags; for a viscous liquid we would use more.

Bag filter or cartridge filter?

Bags suit high flows and heavy solids, and a change-out is quick and clean. Cartridges give finer and absolute ratings. Many plants put a bag filter ahead of a cartridge filter.

Can a bag filter housing be used for oil?

Yes. Allow more bag area for the viscosity, and choose bags and seals that suit the oil.

Vens bag filter housings and bags

• Eco bag filter housing (EBF)

• Top entry bag filter housing (ETPL)

• Side entry bag filter housing (ESDL)

• Multi bag filter housing (EMBF)

• Flash open multi bag filter housing (FOBF)

• Plastic bag filter housings: PP, PVDF and UPVC (PBF)

• Filter bags, 1 to 100 µm

Related guide: How to choose a filter cartridge. See the full Vens filter range.

Customers in the EU are supplied and supported through our European company, VDT Europa OÜ in Tallinn, Estonia.