PVC (Polyvinyl Chloride) is traditionally used in the design of plumbing for pools and spas. There are limitations with PVC. After researching this topic I thought it may be helpful to our readers to see what I discovered. What led me to this pursue this research was during a routine inspection of a client’s pool plumbing after the recent installation of a 400 BTU Heater. See Pics below.
The back-story on the design is this 3/4″ pvc is fed from a 2″ PVC that is within 36″ linear inches from the output of the heater. This 3/4″ PVC acts as a bypass to 3 sensors for a Pulse pH/ORP Controller (Model 7215-01). These sensors monitor and control pH and ORP simultaneously.
TECHNICAL POINT: ORP measures the oxidation level in the water typically as a result of water treatment by Chlorine, Bromine, Ozone, Peroxides, Peracetic Acid, etc., and pH allows optimum conditions for the chemistry to be effective.
After a successful installation of the new Raypak 400 BTU heater our client started use immediately to warm the pool and spa. The heater was installed in Las Vegas in the month of June. As the summer progressed and the outdoor temperatures began to rise, we noticed that the 3/4″ plumbing had bent sometime in the month of August. Temperatures in Las Vegas hover around 110 degrees F, however there are other conditions at play here that contributed to the bending of the PVC.
In this scenario, the ground is covered in landscape stone. During the course of the day the stone absorbs heat from the sun thereby radiating this heat to the base of the 3/4′” plumbing before it goes underground (see picture). If we consider the heat produced from the heater, the constant ambient temperatures exceeding 110 degrees F and the radiated heat from the landscape rock…these tree elements created temperatures exceeding the PVC temperature limitations of 140 degrees F. Although the pipe never burst under the constant 50 PSI operating pressure, the PVC literally bent to the ground.
We will replace the bent PVC and wrap with insulation foam followed by a 10 mil polyvinyl chloride (PVC) tape wrap increase the insulation value. This will provide an insulation benefit in TWO ways. During the summer, the pipe will be protected from the ambient heat and radiant heat of the ground. In the winter, when Las Vegas dips below 32 degrees F (usually 1 week out of the year), the pipe will be protected from possibly freezing and bursting.
What are the markings on PVC pipe?
The outside of PVC pipe must be labeled as follows:
- The manufacturer’s name or trademark
- The standard to which it conforms
- Pipe size
- Material designation code
- DWV if for drainage
- Pressure rating if for pressure
- SDR number or schedule number
- If the pipe is for potable water, a laboratory seal or mark attesting to suitability for potable water
For those standards that cover several products, there must be additional markings to indicate the pipe stiffness number, the SDR, the EB or DB number. A certifier’s mark may also be on the pipe.
Does PVC pipe have a long life expectancy?
Yes, studies on PVC pipe made in Europe in the 1930’s and been in continuous use suggest a very long useful life for these products of a hundred years or more, which will generally exceed the lifespan of the structures they are installed in.
How does PVC pipe behave at different temperatures?
PVC pipe exhibits decreasing pressure rating and stiffness with increasing temperature. As with dimensions, the pressure ratings and published pipe stiffness figures for PVC pipe are listed at an operating temperature of 73F. To determine the pressure ratings and stiffness of PVC pipe at higher temperatures, multiply the pressure rating or pressure class and the stiffness / deflection by the pipes de-rating factors at that temperature. An example of a table of PVC pipe de-rating factors is shown below. Consult with the manufacturer of your pipe for specific data. The typical upper limit for continuous use of PVC pipe is 140 F.
As an example, using the table above, a PVC pipe rated at 450 psi at 73 F, used at 100 F would have a pressure rating of:
450 psi x 0.75 = 337 psi
Does long term exposure to sunlight degrade exposed PVC pipes?
PVC pipe contains stabilizers to protect the pipe against attack by UV present in sunlight. After several months of outdoor exposure a discoloration may appear on the surface of the pipe, however, the performance of the pipe is not affected. After two years of exposure, there is only a slight reduction in the impact resistance of the material. PVC pipe used in permanent outdoor exposures should be protected by a light colored compatible water based paint. Do not use oil based paints.
What are the temperature limitations of PVC pipe?
The maximum use temperature for PVC pressure pipe is 140 degrees F. PVC DWV piping readily withstands the hot and cold water discharges that are normally associated with plumbing fixtures.
|Nominal Pipe Size
|Required Minimum Burst Pressure
|Maximum Operating Pressure
|Schedule 401)||Schedule 802)||Schedule 40||Schedule 80|