Chamber or Membrane Filter Press? How They Differ

The chamber filter press and the membrane filter press look almost the same from outside. Both consist of a pack of filter plates between a fixed and a moving head, closed hydraulically and fed by a pump. The difference lies inside the plates, and it decides how dry the cake becomes and how long a cycle takes. This guide explains how each type works and when the extra cost of membrane plates is justified.

How a chamber filter press works

Each plate has a recess on both sides. When the press is closed, two neighbouring plates form a chamber, typically 25–50 mm deep, lined with filter cloth.

1. Closing — the hydraulic cylinder presses the plate pack together so that the plate edges seal against each other.
2. Filling — the feed pump pumps the conditioned sludge through the central feed channel into all chambers at once.
3. Filtration — the cloth holds back the solids. The filtrate runs through the cloth, along the drainage surface of the plate and out through the filtrate channels. As the cake builds up, the pressure rises to the final filtration pressure, typically between 6 and 15 bar.
4. End of filtration — when the filtrate flow has fallen to a small trickle, the chambers are full of cake and the pump stops.
5. Discharge — the press opens, the plates are shifted one by one and the cakes fall onto a conveyor or into a container.

The dewatering force in a chamber press comes only from the feed pump. That is why the pump matters so much; see our guide to filter press feed pumps.

What a membrane filter press does differently

In a membrane plate the drainage surface is a flexible membrane of polypropylene or rubber. Filling and filtration run as in a chamber press, but only up to a moderate pressure of 6–8 bar. Then the feed stops, and water or compressed air is pumped behind the membranes at up to 15 bar. The membranes bulge into the chamber and squeeze the cake from both sides over its whole surface.

This squeeze has three effects:

• The cake becomes drier, typically by 3–8 percentage points of dry solids.
• The cycle becomes shorter, because the slow final phase of filtration is replaced by a squeeze of 10 to 20 minutes.
• The cake is uniform, even when a chamber was not completely filled.

Most membrane presses use a mixed pack: membrane plates alternate with ordinary chamber plates, so every chamber has one membrane side.

Chamber and membrane filter press at a glance

When the membrane press pays off

• Compressible sludges — biological sludge and metal hydroxide sludge release water slowly under pump pressure alone. The squeeze gains the most with these.
• High disposal cost — a cake with 35 % instead of 30 % dry solids weighs 14 % less. With expensive disposal, the membrane plates are paid back by the saving.
• Required minimum dryness — where a landfill or incineration plant sets a limit, the squeeze gives a safety margin.
• Cake washing — where salts or valuable liquid have to be washed out of the cake, the squeeze before and after washing makes the wash effective.
• Varying sludge — when the solids content of the feed changes, a chamber press may end a cycle with half-filled chambers. A membrane press squeezes them anyway.
• More cycles per day — shorter cycles allow a smaller press for the same sludge quantity.

When a chamber press is enough

• Mineral sludges that dewater easily, such as stone and gravel slurries or lime sludge.
• Small sludge quantities with one or two cycles a day, where cycle time is not critical.
• Plants where simple equipment and low maintenance count for more than the last points of dryness.

Sizing in brief

• Chamber volume per cycle — the daily cake volume divided by the number of cycles per day. The filter press calculator gives a first figure.
• Plate size and number — plates from 470 × 470 mm to 2,000 × 2,000 mm; the chamber volume is reached with fewer large plates or more small ones.
• Chamber depth — 25–30 mm for sludges that are hard to dewater, up to 50 mm for mineral sludges.
• Filter cloth — material and weave are matched to the particle size and the chemistry of the sludge. The cloth decides how clear the filtrate is and how easily the cake releases.
• Conditioning — polymer, or lime and iron salts, dosed ahead of the press. See chemical dosage systems.

Our filter presses are supplied as chamber presses or with a membrane squeeze, complete with feed pump and automatic plate shifting.

Frequently asked questions

How much drier is the cake from a membrane filter press?

Typically 3 to 8 percentage points of dry solids, depending on the sludge. The gain is largest with compressible sludges and small with coarse mineral sludges.

Can a chamber filter press be converted to a membrane press?

Often, yes. If the frame and the hydraulic closing are strong enough, part of the chamber plates can be replaced by membrane plates and a squeeze unit added.

Is the squeeze done with water or with air?

Both are used. Water is the safer medium at high pressure and is standard for larger presses; compressed air is simpler for small presses and lower pressures.

How long do membrane plates last?

Several years in normal operation. Membranes are damaged mainly when a chamber is squeezed empty, which a correct control sequence prevents. On many plates the membrane can be replaced without changing the whole plate.

Is a membrane press harder to operate?

No. The squeeze is one more automatic step in the cycle. The plant needs a squeeze unit and its valves, which are part of the supply.

Send us your sludge type, quantity and the cake dryness you need via our contact page. We will tell you whether a chamber press is sufficient or a membrane press is worth it, and size the press with pump and conditioning.