Yogurt Duplex Filter | Milk Filter

The milk filter (duplex filter) is positioned between the raw milk reception tank and the pasteurizer in a yogurt production line. It removes physical contaminants—animal hair, feed particles, dust, bedding materials—from raw milk before further processing. Shuliy has manufactured and installed over 200 duplex filter units across dairy facilities in Southeast Asia, the Middle East, and Africa.

Dual-Filter Design: Continuous operation | SUS 304 Construction | 100-400 Mesh | 0.3 MPa Rated | Easy Maintenance

Duplex Filter vs Single Filter

The duplex filter consists of two parallel filtration cylinders connected by three-way ball valves at the inlet and outlet. When one cylinder requires cleaning, the operator switches the valves to the second cylinder without interrupting production.

A side-by-side comparison at a 500L/day yogurt facility in Riyadh showed the single filter required 6 filter changes per day at 15 minutes each—90 minutes of total downtime. The duplex filter required two valve switches totaling approximately 5 minutes. Over a 30-day period, this recovered 42.5 hours of production time.

Selection Guide

Factor	Single Filter	Duplex Filter
Daily production	Under 500L	500L and above
Budget	$400-800	$800-2,500
Downtime tolerance	Can stop every 2-3 hours	Continuous operation required
Labor availability	Dedicated operator	Minimal staffing

For operations running more than one batch per day, the duplex configuration is recommended.

Operating Principle

Raw milk enters through the inlet three-way ball valve, distributes between the two cylinders, passes through the mesh screens, and exits as filtered milk through the outlet valve. Each cylinder is equipped with a top-mounted air release valve.

During startup, trapped air reduces effective filtration area by 15-20%. Open the air release valves for 10-15 seconds until liquid begins to seep through, then close.

Operating Sequence

Step	Action	Time	Notes
1	Open inlet valve to Cylinder A	–	Both cylinders clean
2	Open outlet valve from Cylinder A	–	Air release valves closed
3	Open air release valves briefly	10-15 sec	Bleed trapped air
4	Monitor pressure differential	Continuous	Normal: 0.05-0.1 MPa
5	Switch to Cylinder B when pressure rises	30 sec	Turn both valves simultaneously
6	Clean Cylinder A	10-15 min	Remove, rinse, reinstall

The pressure differential between inlet and outlet serves as the primary indicator for cylinder switching. When inlet pressure is 0.2 MPa and outlet drops to 0.12 MPa or below, switch to the clean cylinder.

Filter Mesh Selection

Mesh size determines both the particle size captured and the flow rate through the filter.

Mesh Size	Particle Size Captured	Flow Rate	Best Application
100 mesh	150 microns	100%	Pre-filtration for very dirty milk
200 mesh	75 microns	85%	Standard raw milk filtration
300 mesh	50 microns	70%	Premium yogurt, fine clarification
400 mesh	37 microns	55%	Specialty products, lab-grade

For standard yogurt production, 200 mesh provides adequate filtration of hair, feed particles, and visible sediment while maintaining acceptable flow rates. Raw milk quality from small farms without pre-filtering may require 100 mesh as a first pass. Premium Greek yogurt production benefits from 300 mesh, though cleaning frequency increases from 3-4 hours to 1.5-2 hours between changes.

A 2000L/day facility in Lagos initially specified 400 mesh. Filter changes were required every 45 minutes. Switching to 200 mesh reduced daily filter changes from 16 to 5 with no perceptible change in final product quality.

Technical Specifications

Parameter	Specification
Filter Type	Single or Duplex (Double)
Material	Food-grade stainless steel (SUS 304)
Surface Finish	Polished inner and outer surfaces, Ra ≤ 0.8μm
Design Pressure	0.3 MPa
Working Pressure	0.1-0.25 MPa
Connection Type	Expansion/contraction fittings, clamp connections
Valve Type	Three-way ball valves (SUS 304)
Filter Mesh Range	100-400 mesh (customizable)
Air Release	Top-mounted manual valves
Inlet/Outlet	Sanitary fittings (DN25-DN50)
Operating Temperature	0-100°C

Capacity by Model

Model	Configuration	Capacity (L/hr)	Inlet/Outlet	Weight
SL-MF-1	Single	500-1000	DN25	18 kg
SL-MF-2	Duplex	1000-3000	DN32	35 kg
SL-MF-3	Duplex	3000-5000	DN40	52 kg
SL-MF-4	Duplex	5000-8000	DN50	78 kg

Installation Requirements

Mounting height. Position the filter outlet at least 0.5 meters above the inlet of downstream equipment (typically the pasteurizer). This gravity assist reduces transfer pump load.

Bypass piping. Install a bypass line with a manual valve around the duplex filter. During deep maintenance—gasket replacement, welded seam inspection—the bypass allows continued production.

Drain positioning. The drain outlet should be at the lowest point of the installation with a floor drain directly beneath. Cleaning flushes 20-30 liters of water and debris through this outlet.

Cleaning and Maintenance

After each production run, close inlet and outlet valves, open the drain, and flush each cylinder with warm water (40-50°C) for 2-3 minutes. Remove the mesh screen and rinse under running water. Stubborn residue requires soaking in 2% NaOH solution for 15 minutes followed by thorough rinsing.

Weekly maintenance includes complete disassembly—mesh screens, gaskets, and air release valves. Inspect screens for tears or stretched mesh. A 2-3mm hole allows contaminants through and compromises filtration.

Maintenance Schedule

Frequency	Task	Time Required
After each batch	Flush with warm water, rinse mesh	10 min
Weekly	Deep clean, inspect screens and gaskets	30 min
Monthly	Check welded seams, test valve operation	20 min
Every 500-1000 hours	Replace mesh screens	15 min

Troubleshooting

Problem	Cause	Fix
Flow rate drops 30%+	Mesh clogged	Clean or replace screen
Pressure differential > 0.15 MPa	Dirty filter element	Switch to clean cylinder, clean clogged one
Leaking at cylinder base	Worn gasket	Replace gasket (standard size, $5-10)
Air in filtered milk outlet	Air release valve stuck open	Clean valve seat, replace if damaged
Milk bypassing filter	Damaged mesh or improper seating	Replace screen, ensure proper seating
Valve hard to turn	Milk residue buildup	Disassemble valve, clean with warm water

Applications Beyond Dairy

The duplex filter design is suitable for any liquid requiring particulate removal. Shuliy has installed these units in juice plants in Kenya, breweries in Tanzania, and sauce factories in Vietnam.

Industry	Applications	Typical Mesh
Dairy	Raw milk, yogurt, cream, whey	200-300 mesh
Beverage	Fruit juice, beer, wine	100-200 mesh
Food Processing	Sauces, soups, syrups	80-150 mesh
Pharmaceutical	Liquid medications	300-400 mesh

For non-dairy applications, verify chemical compatibility. SUS 304 handles most food-grade liquids. For liquids with pH below 4 or above 9 over extended periods, SUS 316L is recommended.

Related Products

• Yogurt Production Line – Complete turnkey solution
• Milk Pasteurizer Machine – Sterilizes filtered milk
• Cow Milking Machine – Automated milking source