In water supply, irrigation, water treatment, and industrial water circulation systems, the quality of the incoming water directly affects the operational stability of pumps, valves, pipelines, and downstream equipment. If solid particles, suspended contaminants, or particles of different sizes are not properly removed, they can increase pressure loss, cause clogging, and reduce the overall efficiency of the system.

STF FMA-4000 SF is a Self-Cleaning Hydraulic Screen Filter designed to continuously filter water and perform automatic backwashing when accumulated contaminants increase the differential pressure across the filter. The equipment uses a suction scanner, suction nozzles, and a turbine mechanism to remove contaminants from the filter screen without requiring the cartridge to be removed for cleaning during every cleaning cycle.

The FMA-4000 SF series is available in multiple models from FMA-4003 SF to FMA-4010 SF, with inlet/outlet diameters ranging from DN80 to DN250, and a maximum flow rate of up to 580 m³/h, depending on the model and water quality conditions.

1. Overview of STF Product

1.1. What is STF?

STF – Sistemas de Filtrado y Tratamiento de Fluidos S.L. is a brand specializing in filtration and fluid treatment solutions, with products designed to meet filtration and fluid treatment requirements in various industrial systems.

Within the FMA-4000 SF product line, STF has developed a screen filter combining automatic water-based self-cleaning with automatic control. The design is intended to maintain continuous filtration while minimizing system downtime for filter cleaning.

1.2. Outstanding Features of STF FMA-4000 SF

One of the key features of STF FMA-4000 SF is its self-cleaning mechanism using a suction scanner. When contaminants accumulate on the screen and increase the differential pressure, the controller activates the backwashing cycle. The drain valve opens, creating a pressure differential between the inside of the filter and the outside environment, while the motor rotates the suction scanner shaft. The suction nozzles remove contaminants from the screen surface and discharge them outside through the drain line.

Key features include:

• Water filtration using a filtering screen.
• Automatic cleaning of the filter screen.
• Backwash activation based on differential pressure, time, a combination of pressure and time, or manual operation.
• During the backwashing process, water continues to be filtered and supplied to the system.
• Backwash cycle of approximately 35 seconds with automatic adjustment capability.
• Multiple size options from DN80 to DN250.
• Multiple filtration grades, including screen configurations with free passages of 1000, 500, and 300 µm, as well as mesh sizes of 200, 125, 100, and 74 µm.

1.3. Role in Industrial Systems

In a water system, the filter is generally installed upstream of equipment that needs to be protected against solid particles and contaminants.

STF FMA-4000 SF can serve as a filtration stage within the water line, helping reduce the amount of solid particles entering downstream equipment. The filter configuration includes water inlet, filter cartridge, coarse cartridge, scanner assembly, and water outlet, forming a continuous filtration and cleaning process.

1.4. Suitable Applications

Based on the equipment configuration and technical specifications, the FMA-4000 SF is designed for Water – Group 2, with a maximum fluid temperature of 50°C and a working pressure of 2.5–10 bar.

Therefore, STF FMA-4000 SF is suitable for consideration in water systems requiring filtration at relatively high flow rates and continuous operation.

2. Construction and Operating Principle of STF FMA-4000 SF

2.1. Overall Construction

The FMA-4000 SF consists of multiple components working together to perform two main functions: filtration and self-cleaning.

The main components include:

• Filter housing and lids.
• Filtering cartridge.
• Coarse screen cartridge.
• Suction scanner.
• Suction nozzles.
• Scanner tube.
• Centering shaft.
• Turbine.
• Piston.
• Position sensor.
• Flush valve.
• Backwashing valve.
• Victaulic connection and Victaulic clamp.
• SKY Filter controller.
• Sealing gaskets and connection accessories.

Among these components, the filtering cartridge performs the function of retaining particles on the screen surface, while the suction scanner and nozzle system remove the accumulated contaminants during the backwashing process.

2.2. Main Components

Filtering Cartridge

This is the component directly responsible for the filtration process. STF provides multiple filtration grades, allowing selection according to the requirements of the system.

The filtration surface area varies according to the model:

Suction Scanner

The suction scanner moves in a spiral motion inside the filter during the cleaning process. The nozzles mounted on the scanner create direct suction on the screen surface, removing contaminants from the filter screen.

Turbine and Piston

The turbine is one of the mechanical components of the cleaning system. The piston assembly, position sensor, and associated flow paths work together with the control system to perform the backwashing cycle.

SKY Filter Controller

The controller allows monitoring of the filter status, inlet pressure, outlet pressure, and differential pressure – DP. The operator can also monitor the backwashing status, the reason for the previous backwash, and the remaining time until the next cycle when the time-based backwash mode is configured.

2.3. Operating Principle

The operation of STF FMA-4000 SF can be divided into two main stages: water filtration and self-cleaning.

Stage 1 – Filtration

Water enters through the filter inlet and passes through the filtering cartridge. Particles larger than the selected filtration grade are retained on the screen surface, while filtered water continues to flow through the outlet.

As contaminants accumulate, the resistance across the screen increases, creating a pressure differential between the inlet and outlet sides.

Stage 2 – Backwashing

When the differential pressure reaches approximately 0.3 bar, the system can activate the cleaning cycle based on differential pressure. The drain valve opens, creating a pressure differential between the inside of the filter and the external environment.

A high-velocity water flow passes through the screen in the cleaning direction and is discharged through the nozzles. At the same time, the motor rotates the suction scanner, creating a spiral movement so that the nozzles progressively clean the entire screen surface.

An important feature is that water continues to be filtered and supplied to the system during the backwashing process, allowing continuous system operation.

2.4. Control and Operation

The FMA-4000 SF can use several backwash control methods:

• Differential pressure.
• Time.
• A combination of time + differential pressure.
• Manual backwashing.

Through the control interface, the operator can monitor:

• Press IN.
• Press OUT.
• Differential pressure.
• Backwash status.
• Reason for the most recent backwash.
• Remaining time until the next backwash.
• Pressure trend over time.

2.5. Factors Affecting Performance

The filtration performance of FMA-4000 SF depends on several factors, with the most important being:

• Incoming water quality.
• Actual flow rate.
• Selected filtration grade.
• Amount of contaminants in the water.
• Operating pressure.
• Differential pressure across the filter.
• Piping and system configuration.

In particular, the STF flow-rate table is based on data at a 125 µm filtration grade and is divided according to high, medium, and low water quality. Therefore, model selection should be based on actual water conditions rather than only on pipeline diameter.

3. Outstanding Technical Characteristics of STF FMA-4000 SF

3.1. Materials

The standard material configuration of FMA-4000 SF includes:

• Filter housing and lids: S-235-JR.
• Suction scanner: AISI-304.
• Filtration screen: AISI-316.
• Suction nozzles: PVC.
• Backwashing valves: PP.
• Seals: NBR, EPDM, or Viton depending on configuration.
• Housing surface coated with epoxy-polyester polymerized in oven.
• Bolts/nuts using 5.6, bichromated configuration.

The use of AISI-316 for the filtration screen provides a material configuration suitable for the component directly exposed to the industrial water flow.

3.2. Dimensions and Connections

The FMA-4000 SF series includes five main models:

The specified working pressure is 2.5–10 bar, with a maximum fluid temperature of 50°C.

3.3. Pressure and Temperature

FMA-4000 SF has:

• Min. working pressure: 2.5 bar.
• Max. working pressure: 10 bar.
• Max. fluid temperature: 50°C.

In addition, the technical documentation specifies a design with corresponding pressure and temperature values of PN10–16 bar / 50°C in the equipment declaration section. For actual selection and operation, the specific working limits of the supplied model and configuration should be prioritized.

3.4. Flow Characteristics

At a 125 µm filtration grade, the maximum flow rates of the models are shown below:

These values show that larger models provide not only larger connection diameters but also greater filtration surface areas and higher flow-handling capabilities.

3.5. Backwash Configuration

The backwashing system uses:

• Backwashing valve: G-2″ thread / 2″ NPT.
• Backwash cycle: approximately 35 seconds, automatically adjustable.
• Backwash water flow rate:
  • FMA-4003 SF: 5 m³/h.
  • FMA-4004 SF: 12 m³/h.
  • FMA-4006 SF: 20 m³/h.
  • FMA-4008 SF: 25 m³/h.
  • FMA-4010 SF: 35 m³/h.
• Water consumption per cycle:
  • 48 L.
  • 115 L.
  • 195 L.
  • 240 L.
  • 340 L respectively for the five models.

4. Advantages of STF FMA-4000 SF

4.1. Automatic Self-Cleaning

One of the key advantages of FMA-4000 SF is its ability to automatically perform backwashing when contaminants accumulate on the screen.

Instead of frequently removing the filter cartridge for manual cleaning, the system uses the suction scanner and nozzles to clean the screen directly during operation.

4.2. Continuous Filtration

During the backwashing process, water continues to be filtered and supplied to the system. This is particularly useful for applications where water flow cannot be easily interrupted for filter cleaning.

4.3. Differential Pressure Control

Differential pressure is an important parameter for evaluating contaminant accumulation on the screen. FMA-4000 SF can use DP to initiate the cleaning process, with an activation value of approximately 0.3 bar described in the standard configuration of the documentation.

4.4. Multiple Filtration Grades

Users can select the filtration grade according to system requirements:

1000 µm → 500 µm → 300 µm → 200 µm → 125 µm → 100 µm → 74 µm

Selection should consider the required particle retention size, flow rate, water quality, and allowable pressure loss.

4.5. Suitable for High-Flow Systems

With model sizes from DN80 to DN250 and a maximum flow rate of up to 580 m³/h, FMA-4000 SF can be considered for relatively high-flow water systems.

5. Applications of STF FMA-4000 SF

5.1. Industrial Water Systems

FMA-4000 SF is suitable for filtering water streams where solid particles and suspended contaminants need to be removed before the water enters downstream equipment or processes.

In high-flow systems, the use of a self-cleaning filter helps reduce the need to stop the system for manual filter cleaning.

5.2. Water Treatment Systems

The filter can be installed as a mechanical filtration stage in a water treatment system, depending on the incoming water quality and the requirements of downstream processes.

The selection of 1000, 500, 300, 200, 125, 100, or 74 µm filtration grade should be based on the actual requirements of each system.

5.3. Systems Requiring Reduced Loading on Downstream Equipment

When solid particles are retained at the appropriate filtration grade, the amount of contaminants passing to downstream equipment can be better controlled. This is particularly important when downstream equipment has more stringent water-quality requirements.

5.4. Systems Requiring Continuous Operation

The ability to maintain water flow during backwashing makes FMA-4000 SF suitable for consideration in systems where interrupting the water flow simply to clean the filter is inconvenient.

5.5. High-Flow Water Systems

The FMA-4006 SF, FMA-4008 SF, and FMA-4010 SF models provide DN150, DN200, and DN250 sizes, with maximum flow rates of 270, 410, and 580 m³/h respectively.

6. STF FMA-4000 SF Model Selection

6.1. Based on Water Quality

Water quality directly affects the filtration capacity of the filter. For the same model, the suitable flow rate may vary depending on water quality.

For example, FMA-4010 SF has a maximum flow rate of 580 m³/h, while the reference flow rate under low-water-quality conditions is 240 m³/h at a 125 µm filtration grade.

Therefore, model selection should not be based solely on the maximum flow-rate value.

6.2. Based on Flow Rate

The model should be selected so that its filtration surface area is appropriate for the actual flow rate and water conditions.

Larger models provide greater filtration surface areas:

• FMA-4003 SF: 2,475 cm².
• FMA-4004 SF: 4,950 cm².
• FMA-4006 SF: 7,425 cm².
• FMA-4008 SF: 9,900 cm².
• FMA-4010 SF: 12,375 cm².

6.3. Based on Filtration Grade

If the system requires the removal of smaller particles, a finer mesh or screen grade may be required. However, a finer filtration grade is not always better, because contaminant accumulation and pressure loss must also be considered.

6.4. Based on Pressure and Temperature

FMA-4000 SF is designed with a working pressure of 2.5–10 bar and a maximum fluid temperature of 50°C. These parameters must be compared with the actual operating conditions of the system before selection.

6.5. Based on Installation Conditions

In addition to model and filtration grade, the following factors should be considered:

• Inlet/outlet dimensions.
• Installation space.
• Backwash drain-line arrangement.
• Power supply for the controller.
• Possibility of installing a bypass line, if required.
• Accessibility for maintenance.

7. Installation and Operation of STF FMA-4000 SF

7.1. Pre-Installation Inspection

Before installing FMA-4000 SF into the system, check the model, inlet/outlet diameter, filtration grade, pressure and temperature conditions, and overall condition of the equipment.

The piping, valves, and drain line should also be checked to ensure that they are arranged appropriately for the system design.

7.2. Piping Requirements

The piping should be arranged so that abnormal mechanical loads are not imposed on the filter.

The backwash drain line must be securely connected and capable of discharging water containing contaminants outside the system.

STF also recommends installing a check valve on the outlet side to help prevent water hammer from affecting the filter.

7.3. Power Supply and Control

The FMA-4000 SF control system uses a configuration of 4 AA batteries / 220 VAC 50 Hz, depending on the configuration. Where electrical wiring is required, the work should be performed by appropriately qualified personnel.

Electrical components and the control panel should be protected from water splashing during installation and operation.

7.4. Post-Installation Inspection

The start-up sequence is performed according to the appropriate valve configuration. In the FMA-4000 SF instructions, the initial configuration includes:

1. Inlet valve: OPEN.
2. Outlet valve: CLOSE.
3. Bypass, if applicable: CLOSE.
4. Supply power to the equipment.
5. Check the controller.
6. Perform one manual backwash cycle.
7. Open the outlet valve.

When opening and closing valves during operation, they should be operated slowly and gradually to minimize sudden pressure fluctuations.

7.5. Monitoring During Operation

The following parameters should be monitored:

• Inlet pressure.
• Outlet pressure.
• Differential pressure.
• Backwash status.
• Backwash frequency.
• Actual flow rate.
• Drain-line condition.

Monitoring DP is particularly useful for evaluating contaminant accumulation and the operating condition of the filter.

8. Maintenance and Troubleshooting of STF FMA-4000 SF

8.1. Periodic Inspection

STF provides a preventive maintenance schedule for the FMA system. After 1,000 cleaning cycles, the complete filter should be checked, including valve opening and the effectiveness of the cleaning cycle.

The housing corrosion-protection coating should also be inspected approximately every 12 months, with epoxy-polyester coating reapplied where necessary.

8.2. Filtering Cartridge Inspection

The filtering cartridge should be inspected and cleaned when necessary, particularly after periods when the equipment has been out of service.

If manual cleaning is required, pressurized water can be used. If acid or other chemicals are required, they must be selected and handled appropriately according to the material, safety requirements, and procedures of the system.

8.3. Gasket Inspection

Internal gaskets should be inspected periodically, approximately every 12 months. If gasket deterioration or loss of sealing performance is detected, the gasket should be replaced.

8.4. Turbine and Flow-Path Inspection

The turbine and associated flow paths should be inspected to ensure that blockages do not occur and affect the automatic cleaning cycle.

8.5. Precautions During Long-Term Shutdown

If FMA-4000 SF is not used for an extended period, the equipment should be drained and appropriate procedures should be followed before returning it to operation.

9. Why Choose STF FMA-4000 SF?

9.1. Suitable for High-Flow Water Filtration Requirements

The FMA-4000 SF series includes five models from DN80 to DN250, with maximum flow rates from 110 to 580 m³/h, providing equipment options for systems of different scales.

9.2. Self-Cleaning Design

The suction scanner mechanism combined with nozzles and backwashing helps reduce dependence on manual disassembly for filter screen cleaning.

9.3. Continuous Operation

During the backwashing process, water continues to be filtered and supplied to the system. This is an important advantage for systems requiring continuous water flow.

9.4. Status Monitoring Through the Controller

The SKY Filter controller provides information on pressure, differential pressure, and backwash status, allowing operators to monitor the equipment’s operating condition more easily.

9.5. Easier Maintenance Planning

The equipment structure includes separate components such as the filtering cartridge, suction scanner, turbine, piston, position sensor, flush valve, and control system, allowing inspection and replacement to be carried out by individual component categories.

10. Selecting STF FMA-4000 SF for Actual Systems

To select the appropriate STF FMA-4000 SF, selection should not be based solely on pipeline diameter. A suitable selection process should begin with the actual operating parameters of the system.

Step 1 – Identify the Water Type

Identify whether the incoming water is supply water, circulating water, or a specific industrial water stream, and evaluate the amount of solids/suspended particles present in the water.

Step 2 – Determine the Flow Rate

Determine:

• Average flow rate.
• Maximum flow rate.
• Minimum flow rate.
• Continuous or intermittent operating conditions.

Then compare these values with the flow-rate table for each model.

Step 3 – Determine the Filtration Grade

Determine the particle size that needs to be removed and select an appropriate filtration grade from 1000 µm to 74 µm according to the FMA-4000 SF configuration.

Step 4 – Check Pressure and Temperature

Compare the actual operating conditions with the limits:

• 2.5–10 bar.
• Maximum 50°C.

Manual FMA 4000 SF – TRI 25.Ver…

Step 5 – Check Installation Conditions

Determine the installation location, equipment dimensions, backwash drain line, valve arrangement, power supply, and space required for maintenance.

Step 6 – Consider the Backwash Mode

Depending on operating requirements, backwash can be controlled by differential pressure, time, a combination of both, or manual operation.

11. Conclusion

STF FMA-4000 SF is a Self-Cleaning Hydraulic Screen Filter designed for water filtration systems requiring high flow rates and stable continuous operation. The equipment combines a filtering screen with a suction scanner, suction nozzles, turbine, piston, and SKY Filter control system to perform filtration and automatic cleaning.

With the models FMA-4003 SF, FMA-4004 SF, FMA-4006 SF, FMA-4008 SF, and FMA-4010 SF, connection sizes from DN80 to DN250, filtration surface area of up to 12,375 cm², and a maximum flow rate of up to 580 m³/h, STF FMA-4000 SF provides multiple options for water systems of different scales.

A key feature of FMA-4000 SF is its ability to self-clean without interrupting the water flow during the backwashing process, combined with monitoring of inlet pressure, outlet pressure, and differential pressure through the controller. This makes the equipment a solution worth considering for systems that need to reduce manual filter-cleaning work and maintain continuous operation.

When selecting STF FMA-4000 SF for a specific system, it is necessary to evaluate water quality, flow rate, filtration grade, pressure, temperature, pipeline size, and installation conditions simultaneously. Selecting the correct model and filter configuration will allow the equipment to achieve effective filtration and maintain an appropriate self-cleaning cycle under actual operating conditions.