Filter Press repairs

Discover How to filter press repairs with practical tips on troubleshooting, fixing hydraulic systems, replacing filter cloths, and maintaining equipment for longer service life

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Since a filter press consists of multiple components, it is natural that over time, any part may develop issues and require maintenance or repair. Generally, filter press repairs can be categorized into four main areas, which we will list and examine in detail below:

Structural Repairs of the Filter Press

Main Frame Repairs
Drip Tray Repairs
Main Cover Repairs

Main Frame Repairs

Common problems with the main frame that can impair the proper functioning of the filter press include:

Cracks forming in the metal sheets used in the structure
Weld fractures
Warping or twisting of the frame
Bent legs
Deformed Teflon plate rails

These issues can typically be addressed through welding, grinding, repairs, and restoration.

Drip Tray Repairs:

As explained in previous articles, the drip tray closes during the pressing and dewatering process to prevent water from splashing onto the filter cake. Possible problems with the drip tray include:

1. Failure of the pneumatic cylinders (jacks) preventing the tray from fully closing (see attached images for details).
2. Broken legs or supports of the pneumatic jacks.
3. Bent rods or even the drip tray itself, preventing proper closure.
4. Damaged or worn bearings (typically ball bearings) that, if not greased regularly, can break down (images provided).
5. Faulty pneumatic valves and air supply components inside the pneumatic control panel (images provided).
6. Ruptured pneumatic hoses connected to the tray cylinders.
7. Solenoid valve failures.
8. Electrical faults affecting the tray system.
9. Misalignment or loss of tray calibration.

Main Cover Repairs:

Damage or deformation of the main cover can cause operational issues. For instance, if the cover is not properly closed during the dewatering process, water can splash onto other machine parts, causing potential contamination or safety hazards.

Filter Press Filtration System Repairs

Filter Plates
Filter Cloth
Water Channels
Machine Inlet and Outlet

Filter Plates:

Filter plates are among the most critical components of the filter press. Common issues include:

1.Cracked Teflon Plates:
The plates consist of Teflon frames that compress tightly during operation. Causes of cracking include:

Wear and tear over time
Improper pump operation
Foreign objects in the incoming slurry

When cracked, plates fail to seal correctly, leading to:

Leakage of slurry between plates (known as losing the seal)
Slurry spraying around the machine, causing mess and inefficiency
Damage to filter cloths

2.Broken or Worn Plate Handles:
These handles help position the plates on the rails and maintain their alignment.

3.Corrosion of Plate Handles Over Time.

4.Loose Fastening Bolts:
Bolts that hold the plates together may loosen, causing alignment issues.

5.Broken Outlet Pipes:
Blue-colored pipes installed on the plates channel water and slurry out of the system. Over time or due to accidents, these can break or clog, requiring repair or replacement.

Broken chain bolts between the plates can cause chains to snap. This is critical because, in automatic systems, the jack opens the plates by a fixed distance to allow cake discharge. If the chain breaks, plates may not separate properly, resulting in malfunctions or damage.

Filter Cloth

The cloths that cover the filter plates must always be:

Cleaned daily to remain tidy and properly positioned
Free of tears or holes; damaged cloths compromise sealing and cause slurry to form behind the cloth, resulting in poor filtration
Equipped with intact zipper fasteners that secure the cloth to the Teflon plates; damaged fasteners cause wrinkling and overlapping edges that can tear plates and cause slurry leaks.

Repairs Related to the Hydraulic and Pneumatic Systems of the Filter Press

Filter Press Cylinder (Jack)
Hydraulic Unit
Vibrator System

Filter Press Cylinder (Jack):

One common issue with the filter press jack is insufficient pressure to fully compress the plates. It’s important to note that the required jack pressure is uniquely designed for each machine model.

For example, depending on the size of the Teflon plates, different pressure values are set, such as:

150 bar
160 bar
180 bar
200 bar

Filter presses from Denafnon are generally designed to operate at around 200 bar. The larger the filter plates, the greater the pressure and force required to compress and seal them effectively.

Thus, as plate size increases, more force is needed to ensure proper sealing, and this force requirement determines the structural design of the filter press.

The hydraulic jack itself is designed to exert sufficient force. Larger diameter jacks achieve the required force with lower hydraulic pressure, while smaller diameter jacks require higher hydraulic pressure to deliver the same force. Denafnon’s jacks are typically designed to provide adequate compression force at around 200 bar.

However, sometimes the jack pressure doesn’t reach the required level, causing the internal pressure sensor to fail to detect the necessary pressure. As a result, the PLC does not proceed to the next step in the automatic cycle (such as turning on the pump). This issue can have several causes, which we discuss below.

When the jack pressure fails to rise, subsequent automatic steps do not occur because the sensor does not detect the target pressure (usually 200 bar or a set value), preventing the cycle from continuing. The causes can include:

To diagnose the issue, a pressure gauge installed on the jack can be used to measure internal hydraulic pressure. Monitoring this gauge helps identify the problem. By observing the gauge while using the open/close switch for the filter press plates, we may see the following scenarios:

Scenario 1: Hydraulic pressure in the jack does not reach the required maximum.
Scenario 2: Hydraulic pressure reaches the maximum but quickly drops.

For example, if the gauge shows a pressure below 200 bar (say 180 bar) while the hydraulic unit is running, and when the unit is turned off (switch released), one of two cases occurs:

1.Pressure does not drop: The gauge maintains the pressure at the last measured value (e.g., 180 bar). This usually indicates a problem with internal hydraulic unit components such as the pump or hydraulic valves. Further testing is needed to pinpoint the faulty part.

2.Pressure drops: Pressure falls rapidly after shutting off the unit, suggesting leaks in the hydraulic jack’s internal packing and seals, which fail to hold pressure. In this case, the piston packings likely need replacement.

Jack Leakage:

The jack may leak either:

From the rod end (head of the jack)
From the base end of the jack

Rod End Leakage:
If leakage occurs here, the seals around the jack cap should be inspected and likely replaced to stop the leak.

Base End Leakage:
Leaks from the base often result from broken welds on the jack’s welded base plate. Repair involves grinding and re-welding the base to restore integrity and prevent oil leakage.

Physical Jack Issues:

Other physical or mechanical problems with the jack include:

Unusual noises during operation
Scratches or damage on the jack shaft
Jack sticking or jamming

Such issues require inspection and repair by Denafnon’s expert technicians.

Hydraulic Unit:

Problems with the hydraulic unit are often similar to those seen in the jack, such as:

Pressure not rising above 180 bar during operation
Pressure not dropping after the unit stops

If the pressure fails to rise or hold, the hydraulic unit itself is likely the issue.

Potential causes of hydraulic unit malfunction include:

1. Failure of the hydraulic pump
2. Faulty hydraulic valves
3. Malfunctioning pressure relief valves
4. Incorrect internal unit settings or calibration
5. Unusual noises caused by:

Coupling between motor and pump
The pump itself
The motor

6. Internal leaks within hoses and connections
7. Corrosion on hydraulic unit components
8. Broken or damaged hydraulic unit parts
9. Faulty valves

Filter Press repairs | How to filter press repairs