Plate and Frame Filter Guide: Setup, Operation and Care
How to size, set up, run, sanitize and clean a 40 x 40 cm plate and frame filter. A plate and frame filter (also called a filter press or sheet filter) pushes product through a stack of filter sheets held between plastic plates. It handles anything from coarse clarifying to sterile filtration, depending on the sheets you load.
Most problems with sheet filters come from three things: sheets loaded the wrong way round, a papery taste from sheets that were not rinsed, and pressure that climbs too high. This guide covers all three.
1. Sizing: How Many Plates
The more sheets in the stack, the more filter area, and the more product you can filter before the sheets clog. As a rule of thumb:
| Batch size | Suggested filter size |
|---|---|
| 3 bbl | About 9 sheets |
| 15 bbl | 20 to 30 plates |
| 25 bbl | 30 to 40 plates |
40 x 40 cm filter sizes
| Filter | Filter plates | Filter sheets | Filter area |
|---|---|---|---|
| 20 plate | 18 | 19 | 2.6 m² |
| 30 plate | 28 | 29 | 4.0 m² |
| 40 plate | 38 | 39 | 5.3 m² |
| 50 plate | 48 | 49 | 6.7 m² |
Each size also has two end plates. Plate counts and areas are for Letina 40 x 40 cm filters.
2. Loading the Sheets
- Use only new sheets in good condition, chosen for the clarity you need. Coarse sheets clarify; tight sheets polish or remove microbes.
- Soak the sheets for about 10 minutes in water (or in the product) so they are evenly wet before they go in.
- Get the orientation right. Each sheet has a rough side and a smooth side. The rough side faces the inflow plate, where the unfiltered product comes in. The smooth side faces the outflow plate. A sheet loaded backwards does not filter properly.
- Place one sheet between each pair of plastic plates and tighten the stack with the threaded spindle. Make sure every sheet sits flush between its plates and gaskets.
3. One-Stage and Two-Stage Filtration
A diversion (dividing) plate lets you run two grades of sheet in one pass: product goes through coarse sheets first, then through finer sheets. The coarse sheets catch most of the solids, so the fine sheets last much longer.
| One stage | Two stage | |
|---|---|---|
| Diversion plate | Removed | Installed in the stack |
| Sheets | One grade throughout | Coarse sheets on the inlet side of the diversion plate, finer sheets on the outlet side |
| Inlet and outlet | Inlet bottom right, outlet upper left | Inlet upper right, outlet lower left |
To convert to two-stage, move the discharge fitting from the fixed pressure plate to the movable pressure plate, close the openings left on the fixed plate with the sample tap and closure from the movable plate, and insert the diversion plate. Install it with its closed-off port on the inlet and outlet side of the machine.
To choose sheet grades for each stage, see the Filter Sheet Selection Guide.
4. Rinsing Before You Filter
New sheets can give product a papery taste, and sheets stored somewhere damp can pick up a musty one. Rinsing removes it.
- Run 50 to 100 liters (13 to 26 gallons) of water through the filter.
- In the last 20 liters (5 gallons), add a little citric acid to make about a 0.6% solution, and let it soak into the sheets.
- Push the acid solution out with more water.
- When you start filtering, the product pushes the remaining water out. Take samples at the outlet until it runs pure product, then divert at least the first 20 liters (5 gallons), more on a large filter, so no water ends up in the batch.
5. Running the Filter
Start and stop in the right order
Sheets are damaged by sudden pressure changes, so bring the filter up and down gently.
- To start: switch on the pump, then slowly open the inlet valve, the vent (air release) tap and the discharge valve. Close the vent once no more bubbles come out.
- To stop: close the discharge valve, then the inlet valve, then switch off the pump.
- Use a pump suited to filtration. A pump that surges or pulses can break the sheets.
- Filter product that has been racked off its lees. Lees clog the sheets very quickly.
Pressure limits
| Reading | Guideline |
|---|---|
| Back pressure during filtration | 0.1 to 0.2 bar (about 1.5 to 3 psi) gives good filtration |
| Difference between inlet and outlet gauges | Stop and change sheets at 2 bar (29 psi), or 1.5 bar (22 psi) for sterile filtration |
| Outlet (discharge) gauge | Never above 2.5 bar (36 psi) |
Above 2.5 bar on the outlet, the sheets can break through, and product flows past them unfiltered. As the pressure approaches the limit, close the inlet valve a little to reduce the flow and bring the pressure down, then carry on. Repeat until the flow has dropped right off, then replace the sheets and start again.
Avoid stopping partway through a run. If you must, close the inlet and discharge valves and leave the stack tightened.
6. Hot Water Sanitizing
- Ease the spindle slightly so the stack is not over-tight. This lets water and air pass through the sheets and is gentler on the gaskets, while still sealing.
- Open the water slowly and let it run through the filter and out of every valve, then reduce the flow.
- Once the water reaching the filter is 80 to 85 °C (176 to 185 °F), run it for about 20 minutes. Keep the back pressure at 1 bar (15 psi) or less and watch the gauge the whole time.
- At the end, close the valves and taps except the discharge valve, and cover the discharge with sterile gauze.
- Run cold water through the filter to cool it down, then tighten the plates again.
- When you next filter, divert the first product and filter it again, so you can be sure it has not picked up any taste of water or sheets.
Never loosen the plates or remove them while they are hot. Hot plastic plates deform if they are released and will not go back to shape. Leave the stack tightened until it has cooled.
7. Cleaning and Storage
- Wash the filter with a food-safe detergent before its first use and rinse it well before every run.
- At the end of a run, push the remaining product out with water, with a tray under the plates to catch drips.
- Release the spindle and remove the used sheets straight away, before they dry onto the plates.
- Clean the plates with a soft brush. Never use a wire brush. Stubborn residue softens if the plates soak in very hot water. Rinse well afterward, since a brush cannot reach every corner.
- Wash all valves and taps, unscrew and wash the sight glass, and remove and clean the outlet gauge.
- Store spare plates flat, separated by corrugated cardboard.
Products for Plate and Frame Filtration
Plate & Frame Filters (All Sizes) 20 Plate Filter 30 Plate Filter 40 Plate Filter Pall Seitz Filter Sheets BECOPAD Filter Sheets Plate Gaskets (40 x 40 cm) Replacement Parts