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| Technical Bulletin #1 |
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TB-1 |
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| Subject: |
Page 1 of 2 |
| Pressure Cracking of Pool Liners During Storage |
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| The major type of deterioration that we are aware of during storage of vinyl liners is the development of "pressure cracks" under certain conditions. More recent investigation of this phenomenon has revealed that it is a two phase process:
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| Phase I |
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| 1. |
During Phase I, a heavy crease develops on the inside of a double or triple fold. |
| 2. |
The factors that affect the crease formation adversely are: |
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a) |
Higher Temperature During Storage: the higher the temperature, the |
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softer the vinyl becomes, causing a greater amount of material |
| displacement in the crease area. |
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b) |
Higher Pressures: the greater the weight on the fold, the higher the rate |
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of flow will be. |
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c) |
Time: the longer the fold is under pressure, the deeper the crease will |
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become. |
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| Phase II |
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| Phase II is by far the more critical part of the process and involves the unfolding of the liner and flattening of the creased areas at moderately lower temperatures of 38-50°F.
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| If the liner is not allowed to completely warm up to 70-72°F, the deformed inner loop of the crease, which has become shorter due to creep and is stiffer as a result of the lower temperature, cannot withstand the excess tension caused by the unfolding action, splits open, transforming the crease into a crack. |
| If, however, the liner returns to room temperature, flexibility increases, minimizing the tension on the inner loop and greatly reducing the probability of splits developing. |
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