Basic theory of PVC pressure fittings
Basic concepts and characteristics
PVC pressure fittings are pipe fittings made of polyvinyl chloride resin as the main raw material, with appropriate additives added, and manufactured by extrusion or injection molding. This type of pipe fittings has the following significant characteristics:
Excellent corrosion resistance: can resist the erosion of most acid, alkali and salt solutions
Lightweight design: density is only 1.38-1.45g/cm³, which is 1/5 of steel pipe
Low fluid resistance: smooth inner wall, roughness coefficient is only 0.009
Easy installation: using adhesive or threaded connection, high construction efficiency
Good economic efficiency: comprehensive cost is 30%-50% lower than metal pipes
Pressure level classification
According to national standard GB/T 10002.1-2006 stipulates:
0.6MPa series: suitable for low-pressure transmission systems
0.8MPa series: common pressure levels of conventional water supply systems
1.0MPa series: medium pressure demand occasions
1.25MPa series: high-rise building water supply system
1.6MPa series: high-pressure special application scenarios
Main technical parameters
Operating temperature range: 0℃-45℃ (special formula can reach 60℃)
Thermal expansion coefficient: 0.07-0.08mm/(m·℃)
Thermal conductivity: 0.14-0.15W/(m·K)
Elastic modulus: 2500-3000MPa
Burst pressure: ≥3 times the nominal pressure
PVC pressure fittings types and specifications
Structural classification
Elbow series
90° equal-diameter elbow (DN15-DN400)
45° equal-diameter elbow (DN15-DN300)
Reducing elbow (various specifications)
Tee series
Equal-diameter tee (full specification coverage)
Reducing tee (main pipe/branch pipe combination)
Oblique tee (special flow direction requirements)
Other types
Flange joint (DN50-DN600)
Union joint (DN15-DN200)
Pipe cap (full specification matching)
Connection method
Solvent-based bonding
Threaded connection
Flange connection
PVC pressure fittings selection and engineering design
Selection principle
Pressure matching principle
System working pressure ≤ fitting nominal pressure × 0.8
Water hammer pressure ≤ fitting bursting pressure × 0.6
Medium adaptability
Drinking water system must use food grade materials
Chemical system needs to confirm chemical corrosion resistance
Temperature exceeds 45℃ requires special formula products
Economic considerations
Large diameter (DN ≥ 200) preferably flange connection
Concealed engineering should use solvent bonding
Threaded/flange connection is used for parts that need to be disassembled
Key points of hydraulic calculation
Flow calculation formula:
Q=π×d²/4×v
(Q-flow m³/s; d-inner diameter m; v-flow velocity m/s)
Recommended flow rate range:
Water supply system: 0.6-1.2m/s
Industrial system: 1.0-1.8m/s
Head loss calculation:
hf=λ×(L/d)×(v²/2g)
(λ-friction coefficient; L-pipe length m; g-gravity acceleration)
Installation and construction specifications
Pretreatment requirements
Pipe end processing
Cutting surface verticality deviation ≤1°
External chamfer angle 15°-20°
Thorough burr removal
Cleaning treatment
Acetone cleaning of socket parts
Thread oil treatment of threaded parts
Flange sealing surface inspection
Installation process
Solvent bonding process
Glue coating order: socket first, then plug
Glue quantity control: form a continuous rubber ring
Insertion depth: make obvious marks
Curing time: avoid pressure testing within 24 hours
Key points for thread installation
Sealing material selection:
≤DN50 use polytetrafluoroethylene raw tape
＞DN50 use special thread sealant
Tightening torque control:
DN15: 25-30N·m
DN50: 80-100N·m
Industry application cases
Municipal water supply system
Water supply renovation project in a provincial capital city:
Using DN300PVC pressure pipe fittings
Working pressure 0.8MPa
Total length 28km
No leakage record in 5 years of operation
Industrial circulating water system
Cooling water device in chemical plant:
Medium temperature 35-40℃
Contains trace chloride ions
Using DN200 flange joints
Design life 15 years
This guide comprehensively and systematically introduces the technical characteristics, engineering applications and installation and construction points of PVC pressure pipe fittings, providing practical reference for engineering design, construction and installation, and operation and maintenance personnel.
