The principle of plate and frame filter press and solutions to common faults

Plate and frame filter press, commonly known as plate and frame filter press, is a solid-liquid separation equipment widely used in chemical, pharmaceutical, food processing and sewage treatment fields. The working principle is based on the process of physical compression filtration, and the main structure includes filter plates, filter frames, pressing mechanisms and feeding systems.

1. Structural composition:

The plate and frame filter press is composed of multiple filter plates with convex and concave patterns and filter frames arranged alternately and assembled on the frame.
In simple terms, it consists of the following parts:

Filter plates and filter frames: The core components of the plate and frame compressor, the filter plates are usually fixed, while the filter frames are movable. A closed filter chamber is formed between the two.
Squeezing mechanism: responsible for applying pressure to the filter plate, causing the liquid to be discharged through the filter cloth, and the solid is trapped in the filter chamber.
Feeding system: Feed the material to be filtered into each filter chamber.

2. Workflow

The plates and frames are generally made into squares. There are round holes at the corners of the plates and frames. After assembly and compaction, the round holes at the corners are connected to form a channel for the flow of slurry, filtrate or washing liquid. The two sides of the frame are covered with filter cloth with holes at the four corners. The empty frame and the filter cloth form a space for accommodating filter slurry and filter cake. The filter plate is divided into two types: washing plate and filter plate. There is also a side channel in the round hole in the upper left corner of the washing plate, and the washing water can enter the frame from this channel. For easy identification during installation, small buttons or other signs are often cast on the outside of the plate and frame. Usually, the filter plate is cast with one button, the frame is cast with two buttons, and the washing plate is cast with three buttons. When assembled, the plates and frames are arranged in the order of buttons 1-2-3-2-1-2... The pressing device can be driven by manual, electric or hydraulic transmission.

During filtration, the suspension enters the frame through the dark hole at the corner of the filter frame through the filter slurry channel at a specified pressure. The filtrate passes through the filter cloths on both sides and then drains along the adjacent plate surface to the filtrate outlet. The solids are retained in the frame. When the filter cake fills the filter frame, the filtration stops. There are open and dark flows for filtrate removal. If the filter cake needs to be washed, the washing water can be pressed into the washing water channel and enter between the plate surface and the filter cloth through the dark hole at the corner of the washing plate. At this time, the filtrate outlet at the bottom of the washing plate should be closed. The washing water will pass through the filter cloth-the entire filter cake thickness-the filter cloth on the other side in turn under the pressure difference, and finally be discharged from the filtrate outlet at the bottom of the filter plate. This is the cross-washing method, and its function is to improve the washing effect.

3. Classification

4. Common problems and solutions

1. Plate and frame filter plate loosening or even oil leakage fault analysis: The hydraulic system of the plate and frame filter is mainly to provide pressure. When the oil filling of oil chamber A increases, the piston moves to the left, pressing the filter plate to make it airtight. When the oil filling of oil chamber B increases, the piston moves to the right, and the filter plate of the filter is loosened. Due to precision manufacturing, the hydraulic system of the filter has fewer faults, and you only need to pay attention to daily maintenance. Due to wear and tear, oil leakage will occur every year or so, and then you need to repair and replace the O-ring. Solution: Common hydraulic faults of the filter include pressure maintenance and improper hydraulic cylinder advancement. The main reasons for the failure to maintain pressure are oil leakage, O-ring wear, and abnormal operation of the solenoid valve. The common treatment methods are to remove and check the valve, replace the O-ring, clean and check the solenoid valve, or replace the solenoid valve. Improper advancement of the hydraulic cylinder of the filter is generally caused by air being sealed inside. At this time, as long as the system is evacuated, it can generally be solved quickly.

2. The filter plate of the plate and frame filter moves slowly or even deviates and falls off.
Fault analysis: Too much oil and dirt on the guide rod may cause the filter plate of the plate and frame filter to move slowly or even deviate and fall off.
Solution: At this time, the guide rod should be cleaned in time and greased with butter to ensure its lubricity. One thing to note is that it is strictly forbidden to apply thin oil on the guide rod, because thin oil is easy to fall and make the bottom very slippery. It is very easy for personnel to fall here during operation and maintenance, causing personal injury accidents.

3. Fault analysis of groove marks on the filter plate of the plate and frame filter

After several years of use, the filter plate of the filter machine has some groove marks washed out at the corners for some reason. Once the groove marks appear, they will expand rapidly until they affect the formation of the filter cake. At first, the filter cake becomes soft, and then becomes semi-slurry, and the filter cake cannot be formed.

Solution: Replace the new filter plate or repair it with a repair agent. The repair process is as follows: first, use a small saw blade to clean the groove until the original material of the filter plate is exposed; prepare the repair agent; apply the prepared repair agent to the groove, and apply it slightly higher; quickly put on the filter cloth, squeeze the filter plate together, so that the repair agent and the filter cloth stick together, and flatten the groove at the same time.

4. The plate and frame filter cake is unevenly formed or cannot be formed. Fault analysis
There are many reasons for the plate and frame filter cake to form unevenly or unevenly. Insufficient or too thin feed, or blockage can cause this phenomenon. For these faults, the causes must be carefully investigated, and the exact problem must be found, and then the symptomatic treatment must be given.

Solution: increase feed, adjust process, increase feed, clean filter cloth or replace filter cloth, clean blockage, clean feed hole, clean drain hole, clean or replace filter cloth, increase pressure or pump power, start at low pressure, and continuously increase pressure.

5. The reasons for the damage of the plate and frame filter plate itself
the outlet is blocked by solids or the feed valve or outlet valve is closed during startup, and the pressure has nowhere to leak, causing damage. When the feed is insufficient or the feed contains abnormal solid particles, the plate frame itself may be subjected to excessive force and damaged. The feed port is blocked by sludge that is too thick or dry. There is no medium between the filter plates of the filter, only the pressure of the hydraulic system itself, and the plates are damaged by long-term pressure.

Solution: clean the blockage at the feed port; reduce the volume of the filter plate of the filter to complete a working cycle normally; check the filter cloth of the filter, clean the drain, check the outlet, open the corresponding valve, and release the pressure. Clean and restore the filter plate function.