SDB Type PVC Mixing Element
SDB type PVC mixing element for corrosive water-treatment and pool-chemical service. DN25-DN200, 60°C continuous, cost-effective for HCl, NaClO, and Al₂(SO₄)₃ dosing lines.
Product Overview
The SDB type PVC mixing element is the unplasticized-PVC (UPVC) replacement cartridge used in the SDB family of low-cost corrosive-service static mixers. The element is built from a stack of injection-molded UPVC blades in a half-pitch configuration, with each blade layer rotated 90° to the next. The SDB element is the cost-optimized alternative to the SS316L and PP elements for water-treatment chemical dosing where the duty is well-defined and the operating envelope is moderate.
Material Properties
Unplasticized PVC (UPVC, also called RPVC or PVC-U) is an amorphous thermoplastic with a density of 1.40-1.45 g/cm³, a heat-deflection temperature of 70°C under 1.8 MPa load, and a Vicat softening point of 80°C. The grade used for mixing elements is a Type I Grade I compound per ASTM D1784, with a tensile strength of 50 MPa, flexural strength of 90 MPa, and a chemical resistance spectrum covering HCl below 36%, H₂SO₄ below 70%, NaOH up to 50%, sodium hypochlorite up to 15%, ferric chloride, and aluminum sulfate. The material is not suitable for aromatic or chlorinated solvents, ketones, or esters. UPVC is self-extinguishing (UL94 V-0) and is approved for potable water service under NSF/ANSI 61.
Compatible Housings
The PVC SDB element fits the ywmixing SDB type housing in DN25-DN200, with UPVC flanges (DIN PN10 or ANSI B16.5 Class 150) and EPDM gaskets. The housing and element are both UPVC, which makes the assembly fully recyclable at end of life. The element is also supplied as a drop-in replacement for SS316L elements in light-corrosion service, with PTFE centering spacers. Operating envelope is limited to 6 bar at 20°C, derating to 1 bar at 60°C.
Installation & Replacement Guide
The PVC SDB element is light and easy to handle. Depressurize, drain, and unbolt the end cover. Pull the element out by the central tie-rod extension. Inspect the housing interior for stress cracking or chemical attack; UPVC becomes brittle and whitens when exposed to excessive stress or incompatible chemicals. Fit new EPDM cover gaskets, slide the new element in, and torque the cover bolts in a star pattern to 8 N·m. The full replacement takes 10-15 minutes.
Technical Specifications
| Parameter | Value |
|---|---|
| Material | Unplasticized PVC (UPVC), Type I Grade I per ASTM D1784 |
| Element Geometry | Half-pitch crossed blades, 4-6 blade layers, 90° rotation |
| Blade Thickness | 3.0 mm (DN25-DN50); 4.0 mm (DN65-DN100); 5.0 mm (DN125-DN200) |
| Pipe Diameter Range | DN25 to DN200 |
| Pressure Rating | PN6 at 20°C, derating to PN1 at 60°C |
| Temperature Range | 0°C to +60°C continuous |
| Viscosity Range | 1 cP to 10,000 cP |
| Pressure Drop | ΔP = 0.8-1.5 × empty-pipe ΔP at Re = 1,000-10,000 |
| Mixing Precision | Coefficient of variation σX ≤ 7-10% at L/D = 5, 5 blades |
| Connection Types | Flange (DIN PN10, ANSI 150), wafer, socket fusion |
| Mass (DN100, L/D=5) | 0.7 kg per element |
Applications
The PVC SDB element is the standard replacement for low-pressure corrosive water-treatment duty. Municipal water-treatment plants use the element for sodium hypochlorite dosing (5-15% active Cl₂ at DN50-DN150) and ferric chloride coagulant injection (FeCl₃ at 30-40% concentration). Swimming pool chemical dosing systems use the element in pH adjustment (5% HCl or 5% NaOH at DN25-DN80). Industrial wastewater treatment uses the element in aluminum sulfate dosing (50% Al₂(SO₄)₃ at DN50-DN100) for phosphate removal. Other typical services include electroplating rinse-water pH adjustment, scrubber recirculation in air-pollution control, and aquarium/life-support system chemical injection.