Temperature expansion and contraction in PVC piping systems can be compensated with
- expansion loops consisting of pipes and 90o elbows
- flexible bends
- bellows and rubber expansion joints
- piston type expansion joints
Expansion loops are made of standard pipes and elbows and can be produced on the site and adapted to the actual situation.
The length of the loop can be calculated as
Ll = ((3 E D δl) / (2 S))1/2 (1)
Ll = length of loop (in)
E = modulus of elasticity (psi)
D = outside diameter of pipe (in)
δl = change in pipe length L0 due to temperature change (in)
S = allowable working stress at maximum temperature (psi)
A = Ll / 5 (2)
B = 2 Ll / 5 (3)
Modulus of elasticity for PVC:
- 73oF : 400000 psi
- 100oF : 352000 psi
- 140oF : 280000 psi
Modulus of elasticity for CPVC:
- 73oF : 423000 psi
- 100oF : 385000 psi
- 140oF : 330000 psi
- 200oF : 241000 psi
Maximum working stress for PVC:
- 73oF : 2000 psi
- 100oF : 1240 psi
- 140oF : 440 psi
Maximum working stressfor CPVC:
- 73oF : 2000 psi
- 100oF : 1640 psi
- 140oF : 1000 psi
- 200oF : 400 psi
The temperature expansion of the pipe can be calculated as
δl = α Lo δt (4)
α = expansion coefficient (in/in oF)
Lo = initial length of pipe (ft)
δt = temperature change (oF)
Expansion coefficient for PVC:
- 28 10-6 in/in oF
Expansion coefficient for CPVC:
- 44 10-6 in/in oF
Example - Expansion Loop
The expansion of the PVC pipe can from eq. 4 be calculated as
δl = α Lo δt
= (28 10-6 in/in oF) (300 ft) (12 in/ft) ((140 oF) - (70 oF))
= 7.1 inches
The modulus of elasticity is 280000 psi and the maximum working stress is 440 psi at maximum temperature. The length of the loop can from eq. 1 be calculated as
Ll = ((3 (280000 psi) (2.375 in) (7.1 in)) / (2 (440 psi)))1/2
= 126.5 in
A can be calculated from eq. 2 as
A = (126 in) / 5
= 25.3 in
B can be calculated from eq. 3 as
A = 2 (126 in) / 5
= 50.6 in
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