Determination of Filtration Grade in Woven Screen Filters: Influence of Material, Weave Pattern, and Filtration Rate

Abstract

Screen filters are widely used to retain suspended solids. Their performance depends not only on the nominal aperture size but also on the structural characteristics of the filter element, including material properties, weave pattern, and filtration rate. Although manufacturers typically specify filtration grade using mesh size or micron rating, these nominal values sometimes fail to reflect actual retention efficiency under field conditions. This study evaluated how filtration rate influences the retention efficiency of inorganic particles in eleven woven screen filter elements with different materials and configurations. Tests were conducted under two filtration rates and using particles of different size classes to determine the actual filtration threshold. The removal efficiency was determined by measuring total suspended solids (TSS). Eight of the eleven filters achieved more than 85% efficiency for at least one particle class, while three failed to meet this criterion. Higher filtration rates tended to reduce particle retention, particularly in synthetic filters. Nylon and polypropylene elements often exceeded their nominal filtration grades but were more sensitive to flow variations. Stainless steel filters exhibited consistent performance aligned with specifications. The findings emphasize the importance of experimental validation and support more informed filter selection based on particle size and hydraulic operating conditions.

1. Introduction

Filtration is a solid–liquid separation process in which a fluid passes through a porous medium to retain suspended solids, allowing the clarified fluid to flow through [1]. An effective filter must combine high particle retention efficiency with low head loss, mechanical durability, resistance to abrasion and corrosion, and ease of cleaning [2]. The performance of filtration systems depends not only on the nominal pore size of the filter but also on structural factors such as permeability, weave pattern, and material properties.

Screen or strainer-type filters employ one or more filter elements made of woven or nonwoven fabrics to retain solid particles larger than the nominal aperture size specified by the manufacturer. However, their performance can be compromised in the presence of fibrous or algal debris, which tends to become entangled in the mesh structure, making removal difficult as the packing density increases [3,4]. Some screen filters feature automatic flushing cycles, which are triggered by differential pressure or time intervals and are classified as automatic flushing strainer-type filters [1].

Woven meshes are constructed by interlacing threads in predefined patterns, most commonly plain, twill, or satin weaves—resulting in a consistent and stable filter structure [5]. Metallic woven meshes, particularly stainless steel, are widely used due to their high mechanical strength, pressure resistance, and abrasion durability. In contrast, synthetic woven meshes, typically made from polyamide or polyester, offer greater flexibility and corrosion resistance, although with lower structural strength [6]. Their flexibility also facilitates the release of filter cake during cleaning cycles, reducing both cleaning time and water consumption. However, in the case of synthetic woven meshes, concerns remain regarding the long-term stability of the filtration grade and the filtration rate thresholds required to maintain consistent removal efficiency.

Nonwoven meshes consist of randomly distributed fibers that form a three-dimensional porous structure with high surface area and porosity, enabling efficient retention of particles across a wide range of sizes [7]. These properties allow both surface and depth filtration, with high permeability and retention capacity. Furthermore, the ability to use synthetic fibers with distinct mechanical, thermal, and chemical properties enhances adaptability to varied operational conditions [8]. However, nonwoven filters are more difficult to clean than woven ones, since contaminants are retained within the depth of the structure and are harder to dislodge during routine cleaning procedures.

Given the structural and functional differences among filter materials, the proper selection of screen type is critical to filtration performance. This decision must consider the desired filtration rate, water quality, and operational constraints—particularly in systems with automatic self-cleaning routines. Although finer meshes improve particle retention, they also cause greater head loss and clogging, requiring more frequent cleaning. Thus, achieving a balance between filtration efficiency and operational stability depends on both the material and weave configuration of the screen.

Filter element specifications typically include two indicators of filtration capacity: mesh, defined as the number of openings per linear inch, and micron (µm), which refers to the approximate pore size (1 µm = 10⁻⁶ m). These parameters are inversely related: higher mesh values represent finer meshes, while lower micron values indicate smaller pores, both contributing to enhanced particle retention [9]. Despite their widespread use, recent studies have shown that nominal filtration ratings provided by manufacturers do not always reflect actual retention efficiency under real operating conditions [10]. The determination of filtration grades based solely on geometric and constructive characteristics is subject to uncertainty and varies depending on filter technology. In strainer-type filter elements, filtration grade can be influenced by wire properties (e.g., material, elasticity, cross-section, diameter, and spacing), aperture size, and weave pattern. Moreover, operational variables such as water quality, contaminant type and morphology [11], flow rate, and pressure drop across the filter can all affect retention efficiency and actual filtration grade.

The filtration rate (m³ m⁻² h⁻¹) is another critical parameter, as it simultaneously affects both head loss and particle removal efficiency. However, the relationship between filtration rate and performance, particularly for filters constructed with different materials and weave patterns remains underexplored in the current literature [10]. Most available studies have focused on sand filters, limiting the development of specific technical recommendations for screen filter systems [12,13,14].

This study advances the understanding of how filtration rate influences the retention efficiency of inorganic particles in woven screen filters, considering variations in material, weave structure, and aperture size. Despite the recognized importance of these parameters, there is a lack of systematic studies that evaluate their combined influence on the effective filtration grade of woven screen filters under controlled hydraulic and particle-loading conditions. Previous works have largely focused on sand media filtration or have relied solely on manufacturer-declared ratings, which may not reflect real operational performance. This study addresses this gap by experimentally determining and comparing the effective filtration grades of eleven woven screen elements, differing in material and weave pattern, under two filtration rates. The results provide direct evidence of discrepancies between nominal and actual retention capabilities and establish operational thresholds that can guide the technical selection and application of screen filtration systems.

In this study, a set of woven filter elements was evaluated under two filtration rates using a uniform concentration of suspended particles. For each element, various particle size classes were analyzed to determine the lower threshold of actual filtration grade. The study aimed to assess the performance and operational range of different screen configurations, quantify particle retention efficiency under distinct hydraulic conditions, and propose appropriate operational limits to support the technical application of screen filtration systems.

2. Materials and Methods

The experiments were conducted at laboratory scale in the Hydraulics and Irrigation Laboratory (LHI) of the College of Agricultural Engineering (FEAGRI), State University of Campinas (UNICAMP), Campinas-SP, Brazil, using a test bench equipped with a closed-loop hydraulic circuit, as detailed in the following sections.

2.1. Filter Description

The screen filter used in this study was the FA-20^® automatic self-cleaning model, manufactured by Iavant Equipamentos Industriais e Agrícolas Ltda (Ribeirão Preto, SP, Brazil). The unit is equipped with inlet and outlet connections, having an internal diameter of 80 mm, and its filtering element provides a total filtration area of 272,376 mm². During operation, water flows from the outer surface to the inner region of the screen element, causing suspended solids to accumulate on the external surface of the filtering element.

The screen filter includes an automatic self-cleaning mechanism that is activated once the pressure differential between the inlet and outlet reaches a preset threshold of 50 kPa. The cleaning system is driven by a 0.5 HP electric motor coupled with a gear reducer, which rotates the filter element while brushes assist in removing accumulated particles from its outer surface. The flushed solids are discharged through a dedicated outlet. Although this mechanism is integrated into the filter, it was not evaluated in the present study.

The filter housing is constructed of carbon steel, with both internal and external surfaces coated by electrostatic painting. According to the manufacturer, the operational pressure range is 350 to 1400 kPa. The nominal flow rate varies depending on the filter configuration and application, typically ranging from 7.2 to 100 m³ h⁻¹. If the minimum pressure is not maintained, filtration can still occur; however, the automatic cleaning mechanism will not be activated.

Figure 1 illustrates the main components of the filter.

2.2. Filter Elements

Eleven models of filter elements, composed of different materials and weave patterns, were evaluated, with nominal aperture sizes ranging from 74 to 240 μm. The selected materials include AISI 304 stainless steel, polypropylene, polyester, and polyamide (nylon), considering only woven mesh screens. The selection of filter elements for this study was based on commercial availability, mechanical strength of the materials, and their potential application in automatic filtration systems for the removal of suspended solid particles.

The woven elements consist of interlaced threads following different construction patterns, such as plain weave, twill weave, satin weave, and Dutch weave. Each pattern exhibits distinct characteristics in terms of mechanical strength, shape and pore size, and behavior regarding solids accumulation.

All evaluated filter elements were adapted for installation in the FA-20^® filter, in accordance with the geometry and effective filtration area of this model. Nominal pore size specifications were obtained from the manufacturers and will be compared with experimentally determined removal efficiencies to establish the effective filtration grade of each element. The technical specifications provided by the manufacturers for each element are presented in

Table 1. Technical specifications of the evaluated screen filter elements.

ID	Material	Weave Type	Additional Specifications
REPS 14/102	AISI 304 stainless steel	REPS	Wire diameter: 0.40/0.28 mm
T80	AISI 304 stainless steel	Square twill weave	Number of openings per inch: 80; Wire diameter: 0.14 mm
REPS 16/126	AISI 304 stainless steel	REPS	Wire diameter: 0.36/0.23 mm
N12	Nylon (NSS polyamide)	NSS-12	Number of openings per inch: 112; Wire diameter: 60 µm
T120	AISI 304 stainless steel	Square twill weave	Number of openings per inch: 120; Wire diameter: 0.10 mm
PP120	Polypropylene	Satin weave	Monofilament weave; Basis weight: 300 g/m2; Thickness: 0.57 mm; Air permeability: 40 m3 m−2 min−1
R120	AISI 304 stainless steel	REPS	Number of openings per inch: 24–110; Wire diameter: 0.38–0.26 mm
T150	AISI 304 stainless steel	Square twill weave	Number of openings per inch: 150; Wire diameter: 0.06 mm
R150	AISI 304 stainless steel	REPS	Number of openings per inch: 30–150; Wire diameter: 0.23–0.18 mm
PP200	Polypropylene	Twill weave	Monofilament weave; Basis weight: 300 g/m2; Thickness: 0.58 mm; Air permeability: 40 m3 m−2 min−1
PP240	Polypropylene	Satin weave	Monofilament weave; Basis weight: 300 g/m2; Thickness: 0.57 mm; Air permeability: 40 m3 m−2 min−1

. Furthermore, Figure 2 and Figure 3 illustrate the weave patterns of the tested screen element.

2.3. Test Bench

Experimental tests were carried out using water at a temperature of 20 ± 3 °C in a closed-loop hydraulic system, as shown in Figure 4. The system included a 25 m³ clean-water storage tank and a Worthington 3DBE-83 centrifugal pump driven by a 60 HP, 220 V/60 Hz three-phase motor (Worthington, model 3 DBE-83, Rio de Janeiro-Brazil). The pump featured a 200 mm diameter impeller, operating at a nominal speed of 3550 rpm, with a maximum flow rate of 160 m³ h⁻¹ at a total dynamic head of 80 m.

The main discharge line, with a 100 mm nominal diameter, included a 50 mm branch for particle injection. Flow rate, pressure, and temperature were continuously monitored using a data acquisition system. Flow rate was measured using an electromagnetic flow meter (Siemens, model Sistrans FM Mag 5100 W, Karlsruhe, Germany) (range: 10–200 m³ h⁻¹; accuracy: ±0.5% of the measured value), installed at the filter inlet. Pressure was measured using pressure transmitters located upstream and downstream of the filter, including a differential pressure transmitter (range: 0–100 kPa; accuracy: ±0.5% of full scale). Temperature was measured with a PT100 sensor (range: 0–50 °C; accuracy: ±0.5 °C).

The particle injection system consisted of a 1.5 HP centrifugal motor pump, which acted as a booster to provide the necessary pressure for a Venturi-type injector. This injector introduced sand particles into the main discharge line. The concentrated particle mixture was pre-stored in a 1.0 m³ reservoir, equipped with a 1 HP mechanical agitator. This agitator, installed at the top of the tank to prevent particle sedimentation, operated at a nominal speed of 1720 rpm and was controlled by a 60 Hz frequency inverter.

The injection flow through the Venturi was regulated by manually adjusting 1” gate valves, based on the differential pressure across the injector. This pressure was monitored using gauges installed upstream and downstream of the device. The injected flow rate was determined using a rotameter connected to the injection feed line.

To control the operational conditions during the tests, 4” gate valves were installed on the filter’s inlet and outlet lines, allowing manual adjustments of pressure and flow rate. Additionally, the system includes two ¾” ball valves positioned upstream and downstream of the filter, intended for collecting samples for total suspended solids (TSS) analysis.

2.4. Hydraulic Conditions for Determining Filtration Efficiency and Effective Filtration Grade

Tests to determine filtration efficiency and the effective filtration grade were performed under a constant inlet pressure of 400 kPa for all evaluated filter element models. During testing, solid particles (silica sand) were injected at controlled concentrations ranging from 30 to 145 ± 2 mg L⁻¹, simulating typical operating conditions found in drip and microirrigation systems.

Each filter element was tested under two distinct filtration rates: 187.5 m³ m⁻² h⁻¹ and 375 m³ m⁻² h⁻¹. These rates correspond to 50% and 100% of the recommended filtration rate for the filter element’s use, equivalent to flow rates of 50 and 100 m³ h⁻¹, respectively. The maximum filtration rate was established based on the criteria defined by Cano et al. [15].

2.5. Determination of Filtration Grade

To evaluate the solid removal performance of the filter elements under particle injection conditions, three pairs of approximately 5 L samples were collected upstream and downstream of the filter. Total Suspended Solids (TSS) were determined according to Method 2540 D—Total Suspended Solids Dried at 103–105 °C, as described in the Standard Methods for the Examination of Water and Wastewater [16].

Samples were filtered using Whatman glass microfiber membranes (Whatman, Cytiva, Maidstone, United Kingdom), model GF/C (47 mm diameter), with a nominal pore size of 1.2 µm. TSS concentration in each sample was calculated using Equation (1):

$$TSS={\displaystyle \frac{A-B}{V}},$$

(1)

where TSS is the total suspended solids concentration (mg L⁻¹); A is the final mass of the glass microfiber filter with dried residue (mg); B is the initial mass of the glass microfiber filter (mg); and V is the sample volume (L).

Based on the TSS concentrations at the filter inlet and outlet, the removal efficiency (E_f) was calculated using Equation (2):

$$E_f=100\left(1-{\displaystyle \frac{C_e}{C_s}}\right),$$

(2)

where C_e and C_s are the TSS concentrations at the filter outlet and inlet, respectively (mg L⁻¹).

The selection of particle size ranges for the tests was based on the filtration grades reported by the manufacturers in order to assess filter performance across different size classes. The effective filtration grade was defined as the smallest particle diameter retained with an efficiency ≥ 85% at each tested filtration rate, following the criterion established in filtration performance standards such as ISO 16889 [17] and applied in previous solid–liquid separation studies [18].

The silica sand used in all tests was previously washed, oven-dried (105 °C, 24 h), and fractionated by mechanical sieving using a stack of standardized stainless steel sieves (nominal apertures: 250, 177, 149, 120, 105, 88, and 77 μm). Three narrow particle size classes were selected for each filter element according to the nominal filtration grade declared by the manufacturer, with the selected fractions bounded by two consecutive sieves. Although particle size distributions within each class were not characterized by laser diffraction, the use of calibrated sieves ensured well-defined aperture limits and minimized the presence of particles outside the target range. All sand fractions originated from the same batch to maintain mineralogical composition, density, and particle shape. Visual inspection under a stereomicroscope indicated predominantly subrounded to rounded quartz grains, which reduces the variability in retention efficiency due to particle morphology.

To achieve this, at least three distinct particle size classes were evaluated per filter element, enabling the determination of the lower threshold of effective grade. This approach follows the methodology described by Cano et al. [10].

3. Results

3.1. Filtration Grade and Suspended Solids Removal Efficiency

The experimental results enabled a detailed comparative analysis between the nominal filtration grade specified by the manufacturers and the effective grade observed under operating conditions representative of industrial manufacturing and microirrigation systems. Among the eleven evaluated filter elements, eight demonstrated satisfactory performance, with suspended solids removal efficiency (E_f) exceeding the established minimum threshold. However, significant discrepancies were observed between the nominal and effective values, particularly in elements made of synthetic materials. These findings underscore the importance of experimental validation to ensure the reliability of components used in filtration systems.

Figure 5 and Figure 6 present the results of suspended solids removal efficiency (E_f) as a function of the injected particle size for each filter element, evaluated under two operational flow rates (50 and 100 m³ h⁻¹). The dashed lines indicate the E_f = 85% threshold, adopted as the reference for determining satisfactory filter performance. This approach enables the identification of the effective filtration grade under different hydraulic conditions and provides technical support for selecting appropriate filter elements based on water quality and filtration rate.

As shown in Figure 5, synthetic screen elements exhibit greater variability in performance between flow rates, with some models (e.g., N12 and PP120) outperforming their nominal ratings at lower flow rates, while others (e.g., PP200 and PP240) show reduced selectivity and higher sensitivity to flow changes. These trends suggest that the flexibility and pore structure of synthetic materials can lead to both enhanced fine-particle retention under favorable conditions and performance losses when hydraulic stress increases.

In contrast, Figure 6 shows that metallic screen elements generally maintain consistent performance across both flow rates, with REPS and twill weaves (e.g., REPS 14/102, T80, REPS 16/126, R120) closely matching manufacturer specifications. The smaller standard deviations indicate stable hydraulic behavior and lower susceptibility to deformation under higher flow, confirming the greater dimensional stability of stainless steel meshes compared to synthetic counterparts.

Together, Figure 5 and Figure 6 highlight the distinct operational profiles of synthetic versus metallic screens. While certain synthetic elements can surpass nominal performance under optimal conditions, metallic elements offer more predictable retention across a wider range of filtration rates. This reinforces the importance of considering both material and operational parameters when selecting filter elements for specific applications.

A direct comparison between plain weave and twill stainless steel screens with similar nominal grades indicates that twill weaves tend to reach slightly higher efficiencies, particularly for fine particle retention. This effect is likely related to the increased tortuosity of the pore paths and smaller effective pore openings in twill structures compared to plain weaves. Although the performance advantage was modest, it was consistent across replicates, suggesting that weave geometry has a measurable influence on retention mechanisms, independently of filter material. These findings are consistent with the structural parameters summarized in Table 1 and with the efficiency patterns observed in Figure 2 and Figure 3.

Relevant differences were observed between the nominal effective filtration grade provided by manufacturers and the actual values obtained experimentally, particularly for filter elements made from synthetic materials. This discrepancy underscores the importance of experimental testing as an essential tool for validating filtration components used in irrigation systems, in agreement with findings reported by Ribeiro et al. [19].

Filter elements made from AISI 304 stainless steel, especially those with REPS and twill weave patterns, demonstrated high performance stability, with effective filtration grades closely aligned with manufacturer specifications, even under varying flow rate conditions. This operational consistency is attributed to their high structural rigidity, abrasion resistance, and precise control of pore openings, characteristics that provide greater predictability in the filtration process [20,21].

In contrast, elements manufactured from synthetic materials such as polypropylene and polyamide exhibited variable performance relative to their nominal ratings. This behavior is associated with the greater flexibility of synthetic fibers, irregularities at thread intersections, and heterogeneity in pore distribution.

Another critical aspect observed was the influence of filtration rate on particle removal efficiency. Elements such as REPS 14/102 and T80 performed better at the lower flow rate (50 m³ h⁻¹), demonstrating the ability to retain particles finer than their nominal rating. However, when operated at 100 m³ h⁻¹, the effective filtration grades matched the specified value, indicating that increased filtration rates may reduce mesh selectivity. This behavior is consistent with the findings of Zhenji et al. [22], who reported decreased filter cake thickness and retention efficiency at high flow velocities due to intensified hydrodynamic drag forces.

N12 and PP120 elements, made from synthetic fibers, outperformed manufacturer specifications by effectively retaining smaller particles with high efficiency. This enhanced performance may be attributed to the lower rigidity of the fibers, which can lead to partial collapse of the porous structure and increases the likelihood of retention by direct interception. However, this same characteristic may also result in higher susceptibility to clogging and mechanical degradation over time, particularly under high-flow conditions or in the presence of organic matter.

Experimental results confirmed that the REPS 14/102 and T80 models, with nominal filtration grades of 250 μm and 177 μm, respectively, had these values experimentally confirmed under the flow rate of 100 m³ h⁻¹. However, when operated at 50 m³ h⁻¹, they exhibited superior performance, retaining particles of 177 μm and 149 μm with suspended solids removal efficiencies (E_f) of 94.33% and 94.58%, for each filter element.

The T120 element, designed to retain particles of 125 μm, demonstrated the ability to remove smaller particles, specifically 105 μm, with efficiencies of 92.76% and 85.61% at flow rates of 50 and 100 m³ h⁻¹, respectively. Similarly, elements REPS 16/126, R120, and R150 met expectations based on the values declared by the manufacturers (177, 125, and 105 μm, respectively), presenting removal efficiencies ranging from 89.57% to 97.70% under both tested filtration rates. These results underscore the reliability of these models under varying operational conditions.

On the other hand, the T150 element, characterized by a square weave, was the only filter element that underperformed relative to its nominal specification. Although it was rated to retain particles as small as 105 μm, the experimental results indicated that it effectively retained only 125 μm particles, with E_f values of 93.03% and 91.07% under the two flow conditions.

The PP240 element, also with a satin weave and designed to retain 63 μm particles, showed even more limited performance. Experimental data revealed effective retention only for 149 μm particles, with E_f values of 87.30% and 89.59% under the two test conditions, revealing a significant divergence from the manufacturer’s specifications.

The experimental results confirmed that stainless steel elements with REPS and twill weaves (such as REPS 14/102, T80, REPS 16/126, and R120) exhibited effective filtration grades in good agreement with the values declared by the manufacturer, maintaining consistent performance across both tested flow rates. This consistency suggests a more predictable performance of these elements, regardless of filtration rate. Stainless steel monofilament screens with plain Dutch weave exhibit high thermal, chemical, and mechanical resistance, making them suitable for liquid-solid separation under high pressure environments. For these reasons, they are widely used in the food, pulp, and agricultural industries. In these waves, filtration occurs at the intersection points between longitudinal and transverse wires, where triangular openings allow the flow of the influent [23].

In contrast, elements made from synthetic materials, such as polypropylene and polyamide, showed significant variations between nominal filtration grades and the experimentally obtained results. The N12 element, manufactured from nylon, outperformed its declared specification: although designed to retain particles down to 125 μm, it effectively retained 88 μm particles, achieving E_f values of 92.5% and 90.17% at flow rates of 50 and 100 m³ h⁻¹, respectively. Similarly, the PP120 element, made of polypropylene with a satin weave, exhibited comparable performance, retaining particles smaller than declared (125 μm), with E_f values of 90.70% and 94.33% for particles of 74 and 88 μm, respectively, under the same test conditions.

Finally, the synthetic elements PP200 and PP240, which were designed to retain the smallest particles among the tested materials, exhibited performance below expectations. The PP200 element, featuring a twill weave and declared to retain particles of 74 μm, demonstrated effective retention only for 88 μm particles at a flow rate of 50 m³ h⁻¹, with an E_f of 88.29%. In tests conducted at 100 m³ h⁻¹, the efficiency increased to 95.25%, but for 125 μm particles, indicating a loss of nominal retention capacity under higher filtration rates.

3.2. Effects of Filtration Rate on Particle Removal Efficiency

Among the eleven evaluated filter elements, five showed changes in their effective filtration grade in response to increased filtration rates.

Table 2. Comparative summary of the filtration grade declared by the manufacturer and the experimentally determined grade according to test flow variation for each filter element.

ID	Manufacturer-Specified Filtration Grade (μm)	Test Flow Rate (m3 h−1)		Flow Rate (m3 h−1)
		50	100	50	100
		Experimentally Determined Filtration Grade (μm)		Filter Performance Classification
REPS 14/102	250	177	250	High	High
T80	177	149	177	High	Moderate
REPS 16/126	177	177	177	Moderate	Moderate
N12	125	88	88	High	High
T120	125	105	105	High	Moderate
PP120	125	74	88	High	High
R120	125	125	125	Moderate	Moderate
T150	105	125	125	Moderate	Moderate
R150	105	105	105	Moderate	Moderate
PP200	74	88	125	Low	Low
PP240	63	149	149	Low	Low

presents a comparison between the manufacturer-declared filtration grades with the values experimentally determined for each element under two flow rate conditions (50 and 100 m³ h⁻¹).

The performance classification presented in the “Filter performance classification” column was established based on the suspended solids removal efficiency (E_f) determined experimentally for each filter element. The following thresholds were adopted: elements were classified as “high” when they exhibited an E_f ≥ 90%, indicating superior performance and high reliability in retaining suspended particles. Filters with “moderate” performance were those with efficiencies in the range of 85% ≤ E_f < 90%, reflecting acceptable but slightly reduced retention capabilities. Lastly, elements were categorized as “low” performance when E_f < 85%, indicating suboptimal filtration efficiency and potential limitations in retaining fine particulate matter under operational conditions.

Elements such as REPS 14/102 and T80 outperform their nominal specifications at the lower flow rate of 50 m³ h⁻¹ by retaining smaller particles than expected, indicating improved separation efficiency under reduced hydraulic stress. However, under the higher flow rate, the effective filtration grade matched the nominal value, indicating a loss of selectivity as the filtration rate increased.

The REPS 16/126, R120, and R150 elements demonstrated consistent performance under both tested conditions, confirming the reliability of the effective filtration grades reported by the manufacturer. Notably, the N12, T120, and PP120 models exhibited superior performance, retaining smaller particles than their nominal ratings, with removal efficiencies that remained stable or only slightly affected by variations in flow rate. Conversely, synthetic fiber elements (e.g., PP120, PP200, PP240) tended to show greater sensitivity to flow variations. Their effective filtration grades increased at higher flow rates, suggesting reduced selectivity and potential deformation of the pore structure under elevated hydraulic loads.

The T150 element showed the least favorable performance, retaining only larger particles than declared at both flow conditions. This suggests limitations in material rigidity or weave integrity affecting filtration efficiency.

Overall, these results highlight the impact of filtration rate on the effective separation grade of screen filters and underscore the necessity for experimental validation tailored to real-world operational scenarios, particularly in irrigation systems, where water quality and flow conditions can vary widely.

4. Discussion

4.1. Filtration Grade and Suspended Solids Removal Efficiency

The results obtained are consistent with those reported by Cano et al. [15], who demonstrated that fabrics made from polypropylene (PP) monofilament threads demonstrate greater flexibility compared to metallic meshes. This characteristic favors the detachment of particles and impurities during cleaning cycles, improving the removal of the filter cake. Additionally, PP fabrics are lighter and exhibit good chemical resistance, which makes them advantageous in environments with corrosive agents. However, they present lower resistance to mechanical abrasion and are more susceptible to aging when compared to stainless steel meshes.

The pore size distribution and overall porosity of textile filter media play a crucial role in filtration performance. In such materials, finer pores combined with high porosity are typically associated with smaller fiber diameters. When the pore size becomes smaller than the fiber diameter, porosity is significantly reduced, which compromises permeability. Conversely, reducing fiber diameter promotes the formation of finer pores while maintaining adequate porosity, thereby improving filtration efficiency without severely impacting flow capacity [24].

Furthermore, materials with smaller pore sizes are more susceptible to early clogging, which necessitates more frequent cleaning and may compromise the system’s operational stability. In contrast, materials with broader pore size distributions, such as REPS meshes, commonly referred to as plain Dutch weave, combine threads of varying diameters to form structures with both fine and coarse pores. This configuration facilitates both effective particle retention and adequate flow, resulting in more efficient filtration, as observed in the REPS 14/102 and REPS 16/126 elements. In this setup, larger particles are retained in the outermost layers, while smaller particles penetrate deeper into the filter matrix, delaying surface saturation and extending the filtration cycle [25].

In this context, En-Nabety and Boudi [26], using computational fluid dynamics (CFD) modeling, confirmed the relationship between flow, pore size, particle characteristics, and retention efficiency in mechanical bar screens used for wastewater filtration. The authors demonstrated that screens with smaller pore size provide greater retention capacity, especially for fine particles, compared to screens with larger openings.

Moreover, they highlighted that filtration efficiency is influenced not only by particle size but also by particle density: larger and denser particles tend to be more easily retained due to their lower susceptibility to drag forces. On the other hand, high inlet fluid velocities reduce filtration efficiency by promoting the passage of fine particles through the openings. These findings underscore the importance of selecting appropriate bar spacing based on both the physical properties of the suspended solids and the hydraulic operating conditions, to optimize filtration performance and minimize the risk of clogging.

Overall, the selection of the filter element should be based not only on the nominal pore size but also on operational parameters, including filtration rate, the type and size distribution of suspended particles, and the frequency of automatic cleaning cycles. This integrated approach helps maintain water quality while minimizing head loss and reducing the frequency of self-cleaning operations. Screens with higher porosity, such as REPS type, tend to combine high removal efficiency with lower head loss, thus extending the interval between self-cleaning cycles and reducing the system’s operational costs. Furthermore, the internal geometry of the weaves directly influences flow distribution and particle behavior during the retention process.

Experimental results from the present study confirm that filtration efficiency is governed by the interaction between the physical characteristics of the filter medium (such as material, weave pattern, and pore distribution) and the hydraulic operating parameters (including flow rate and suspended solids concentration). As such, experimental determination of the effective filtration grade is essential for identifying potential limitations in manufacturer-provided specifications and for guiding the accurate selection of filter elements. Thus, the adoption of more rigorous technical criteria, supported by standardized tests conducted in controlled environments or under representative operating conditions, contributes to the reliability of filter elements by ensuring more predictable performance, compatibility with the characteristics of the fluid being filtered, and greater efficiency in solid–liquid separation processes across various industrial and environmental applications.

In summary, the experimental data demonstrated that most of the evaluated screen filter elements performed at or above the expected efficiency thresholds under realistic hydraulic conditions. However, notable variability was observed, especially among synthetic materials, highlighting the limitations of relying solely on nominal ratings for filter selection. The results emphasize the importance of considering both the filtration rate and the structural characteristics of the filter element, particularly the weave pattern and material rigidity, when evaluating filtration performance. These findings support the adoption of experimental validation protocols and reinforce the need for more transparent and standardized manufacturer specifications to guide the proper selection of screen filters in filtration systems.

It is important to note that downstream particle size distributions were not measured directly in this study. Instead, the effective filtration grade was inferred from TSS measurements of mono-fractional particle feeds prepared by standardized sieving. Although this approach ensures consistent and well-defined particle size inputs, direct outlet size characterization (e.g., by laser diffraction or image analysis) would improve the precision of threshold determination and enable formal uncertainty quantification. Future work should incorporate such analyses to complement TSS measurements and provide more robust statistical confidence in filtration grade estimates.

The present study did not include quantitative measurements of particle shape descriptors, density variations, or surface chemistry. However, these variables were controlled by sourcing all test particles from the same batch of washed and oven-dried silica sand, composed predominantly of quartz with an estimated density of 2.65 g cm⁻³ and visually classified as subrounded to rounded grains. This uniformity in mineralogy and morphology minimizes variability in particle–mesh interactions beyond that caused by size differences. Nevertheless, future work should incorporate quantitative characterization of particle morphology, density, and surface properties to further clarify their influence on filtration efficiency and retention mechanisms.

4.2. Effects of Filtration Rate on Particle Removal Efficiency

The filtration rate affects not only the solids removal; it also affects the system’s operational stability. High filtration rates can compromise particle retention performance, as demonstrated, because the increased water velocity may dislodge previously captured solids, thereby reducing overall system efficiency. Therefore, defining appropriate operational limits is essential to ensure a balance between filtration efficiency and durability of screen filter elements.

According to Zhenji et al. [22], increasing the flow rate amplifies the flow field forces acting on suspended particles. This promotes their transport through the filter body and reduces the likelihood of adhesion to the filter mesh surface. Consequently, even under the same particle concentration, the thickness of the filter cake layer tends to decrease as the flow rate increases, thus compromising the efficiency of suspended solids retention. This effect is particularly relevant in filter elements where the screens are made from materials with higher elastic modulus, such as nonwoven meshes, or when the intersections between warp and weft threads exhibit greater flexibility, as observed in plain, twill, and Dutch weave.

REPS combines a relatively fine weft (crosswise wire) with a coarser warp (longitudinal wire), creating a mesh with high mechanical strength and a dense network of pores with narrow, wedge-shaped flow paths. This configuration allows for efficient particle retention by capturing larger particles on the surface and enabling smaller particles to be trapped within the porous structure, resulting in a more gradual clogging pattern and improved filtration efficiency. Compared to twill and satin weaves, REPS structures offer greater dimensional stability, higher resistance to deformation under pressure, and a more uniform flow distribution, which collectively enhance operational reliability and particle separation performance.

The relationship between solid removal efficiency and filtration rate has been widely explored by various authors. In general, it has been demonstrated that filtration efficiency in metallic screen elements is affected by flow rate and fluid velocity [27]. As the magnitude of these factors increases, solids removal efficiency tends to decrease, primarily due to the rise in drag and shear forces. These forces hinder particle retention and promote their detachment from the filter surface. In screen filters, the structure of the element itself offers resistance to flow, flattening the velocity profile and amplifying this effect as mesh permeability decreases.

In parallel, higher flow rates lead to increased head loss not only in a clean filter element but also during prolonged operation, due to elevated frictional forces. Therefore, the relationship between filtration efficiency and head loss must be carefully considered in the design and operation of systems employing screen filters, to ensure a proper balance between hydraulic performance and solids removal efficiency [28].

At low filtration rates, hydrodynamic drag forces are lower than the frictional forces acting on particles, resulting in high retention efficiency. However, as filtration rate increases, drag forces may exceed frictional forces, causing particle slippage or fragmentation and increasing the likelihood of detachment. This effect is especially pronounced for larger particles, which are more susceptible to dislodgement due to the greater hydrodynamic forces acting upon them. Consequently, higher filtration rates tend to increase the average particle size observed in the effluent [28].

Flow velocity is another factor that significantly influences permeability by inducing deformation in the screen structure, which in turn affects particle retention capacity. Ängeslevä et al. [29] experimentally investigated the permeability of different woven screens and compared the results with numerical simulations. The authors found that maximum flow velocity occurred at the center of each pore and, despite applying the same pressure across all samples, each pore behaved as an individual flow channel, exhibiting distinct velocities and flow rates. Overall, the study demonstrated that increasing pore diameter led to higher flow velocities and volumetric flow rates, reinforcing the critical role of mesh geometry in governing flow dynamics.

On the other hand, a material’s filtration capacity is directly related to its permeability, which is the property of porous media to transmit fluids under a pressure gradient. Higher permeability is desirable, because it reduces head loss, facilitating fluid flow with lower resistance. This characteristic is closely associated with the material’s porosity: the greater the porosity, the higher the fluid flow through the filtering medium. Porosity, in turn, depends on the blocking efficiency of the threads, which is determined by their diameter and the geometry of its cross-section [27,30,31].

There are five mechanisms by which particles can be captured: direct interception, inertial impaction, diffusion, electrostatic attraction, and gravitational deposition. The primary function of the filter medium is to retain particles of different sizes. These five filtration mechanisms can act simultaneously, or one may predominate, depending on the characteristics of the particles, such as size and type of electrical charge. As particle size increases, the mechanisms of inertial impaction, gravitational deposition, and direct interception mechanisms become more effective. Conversely, as particle size decreases, the diffusion mechanism plays a predominant role in particle capture [32].

Self-cleaning filters primarily rely on direct interception, wherein particles are retained when they pass close enough to the fibers of the filtering medium. This occurs when a particle follows the fluid streamline and comes within a distance equal to or less than half its diameter from a fiber, resulting in physical contact and subsequent retention [33].

Filtration system operators face the persistent challenge of increasing operational flow rates without compromising solid particle removal efficiency. However, this optimization is limited by physical constraints inherent to the filter element, where the open area is determined by the number and size of pores available on a fixed dimension surface. Traditionally, the main adjustable variable has been pore diameter. But while reducing pore size enhances filtration efficiency, it also increases flow resistance. From a physical standpoint, it is impossible to force more fluid through an opening than its cross-sectional area allows. Thus, smaller pores result in lower achievable flow rates, highlighting the need for careful balancing between hydraulic capacity and separation efficiency.

The advancement of manufacturing technologies, coupled with the ongoing demand for enhanced material performance driven by market needs, has significantly influenced the development of woven composites. Over the past decade, the use of three-dimensional (3D) woven fabrics has garnered increasing attention, particularly in filtration applications.

Three-dimensional woven structures represent a notable improvement over conventional two-dimensional (2D) weaves, offering superior mechanical properties and structural performance. Similarly to 2D woven fabrics, 3D wovens are manufactured using four principal weave architectures: (a) orthogonal, (b) through-the-thickness angle interlock, (c) layer-to-layer angle interlock, and (d) full interlaced. These types of structures exhibit greater internal cohesion, remarkable resistance to delamination, high damage tolerance, and enhanced structural integrity. These characteristics overcome the limitations of traditional laminates, where delamination is a recurring failure mode [34,35,36].

The enhanced mechanical properties of 3D woven structures are intrinsically linked to their complex architecture, which incorporates warp and weft yarns and, in some designs, binder yarns oriented through the thickness. This multilayered arrangement increases stiffness and toughness along the thickness axis, enabling more efficient absorption of impact energy and a progressive failure response, contrasting with the abrupt failure typically observed in laminated materials [37,38].

Three-dimensional (3D) woven screens offer a significant advantage over conventional flat meshes by doubling the open surface area available for filtration, which directly results in a twofold increase in the filtration rate [39,40,41]. This feature provides three relevant operational benefits: (i) it allows for processing up to twice the fluid volume per unit of time without needing to expand existing infrastructure; (ii) it halves the time required to filter a specific volume, enabling increased production frequency in batch operation systems; and (iii) it makes it feasible to specify smaller equipment in new projects or when adapting existing systems without compromising and even surpassing the originally projected flow rate.

Given these potential benefits, future research should explore the application of three-dimensional woven screens in automatic screen filtration systems across various industrial sectors, with the goal of assessing their hydraulic performance and particle retention efficiency under real operating conditions.

Although the application of three-dimensional woven screens represents a significant advancement over the types of filters evaluated in this study, it is equally necessary to propose more immediate and incremental research steps. These include field validation of the experimentally determined filtration grades under dynamic and variable water quality conditions, as well as systematic testing of fouling resistance to assess the performance of filter elements over extended operational periods. Additionally, mechanical resistance tests should be conducted to characterize the structural behavior of the filter screens under different pressure regimes. Such tests are essential to evaluate potential deformations that may occur during operation, which could alter the pore geometry and, consequently, compromise the screen’s permeability and filtration efficiency. These complementary investigations will help establish a more robust technical foundation for selecting and designing durable and efficient filter media for automatic screen filtration systems in diverse industrial applications.

It is worth noting that this study focused on homogeneous inorganic particles to isolate the effects of filter material and weave pattern. However, the presence of organic matter (e.g., algae, biofilms) or mixed particulates could alter retention mechanisms, particularly in flexible synthetic filters where adhesion and clogging behaviors differ [2]. Future studies should evaluate particle mixtures with varying sizes/densities, and organic contaminants to quantify their impact on head loss and self-cleaning frequency.

Although this study focused primarily on the influence of pore size, weave pattern, and filtration rate on particle retention, it is important to recognize that surface interactions also play a crucial role in the clogging of synthetic woven screens (PP/Nylon). Recent research on inorganic–organic hybrid membranes has demonstrated that interfacial charge modulation can significantly reduce colloidal adhesion [42]. Although developed in the context of ion-exchange membranes for flow batteries, these findings provide a valuable conceptual framework that could be extended to woven screen filters. Surface modification strategies, such as plasma treatment or hybrid coatings on polymeric meshes, may represent promising approaches to mitigate organic fouling and enhance the long-term performance of synthetic screen filters.

Moreover, quantifying the long-term performance decay of woven screen filters under dynamic hydraulic conditions remains an important challenge. Future studies should develop durability assessment protocols that integrate accelerated aging tests with dynamic operating modeling, particularly to account for the effects of intermittent high-velocity pulses, particle impact, and structural fatigue on filter integrity. Adapting state-estimation frameworks from durability research may provide a useful approach to predict filter service life by correlating head loss growth with cumulative particle load. Such methods would allow more robust engineering recommendations regarding the stability and operational lifespan of woven screen filters.

Despite these limitations, our results provide critical benchmarks for filter selection under controlled inorganic loads, which represent a worst-case scenario for abrasion and mechanical fouling in filtration systems.

5. Conclusions

The synthetic filter elements N12 (polyamide) and PP120 (polypropylene) exhibited superior performance in retaining suspended solids compared to their nominal ratings, demonstrating their potential as viable alternatives to stainless steel elements—particularly in systems predominantly exposed to inorganic particles. Their lower commercial cost further enhances their applicability in irrigation and water treatment systems.

The experimental results demonstrate that filtration efficiency and system stability are highly dependent on the interplay between pore size and filtration rate. Specifically, when filters operate under conditions that reduce the effective pore size, whether due to particle load or material deformation, head loss and internal flow velocity increase. These effects intensify particle fragmentation and compromise the element’s long-term performance. Therefore, selecting a mesh size with a filtration rating that adequately corresponds to the particle size present in the water allows the clogging process of the filter element to be prolonged, minimizing unnecessary cleaning cycles, promoting rational water use, and reducing maintenance costs.

The findings emphasize the importance of conducting specific experimental evaluations for each filter element type. Reliance solely on manufacturer-declared ratings can lead to inaccurate assessments of filtration capacity and improper system sizing.

This study successfully determined the effective filtration grade for all evaluated elements and proposed operational limits based on filtration rate and particle size distribution. These results provide valuable technical support for the appropriate selection and sizing of screen filters in microirrigation and other water treatment applications, ensuring consistent performance and system efficiency.