MAX-24-Dean
Veteran Member
How to calculate thermal expansion or contraction in Sch. 40 PVC. See attached. This is for electrical PVC, but the same calculation is used for all PVC pipe.
Help! Micro hydro pipe expansion
- Thread starter Ktm rider
- Start date
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There is a trench. I looked into expansion joints. Unfortunately they are WAY out of my budget. I really wanted to put water to it before burying it to check for leaks But I guess I will know if it’s leaking either way.
I should have mentioned that I did install Fernco fitting in both places where it separated. theyre both in the first half of the run. However the latest separation came close to the bottom. So I. A bit concerned about the pressure on this Fernco. I may install one with the stainless reinforcement sleeve.
I posted some pics in a different thread a while back. Just search micro hydro
sea2summit
Elite Member
This thread is realative to my interests.
Is the water level above your feedpoint changing or constant?
Is the water level above your feedpoint changing or constant?
i have another thread explaining my whole system. Just search MicroHydro Project
jigs_n_fixtures
Veteran Member
Mound the pipe backfill, leaving the joints exposed. PVC has a fairly large thermal expansion coefficient and doesn’t like changes in temperature.
For example, the coefficient of thermal expansion for PVC (3.38 x 10-5 in./in./°F) is almost three times as high as for aluminum and six times as high as for steel. Thermal expansion and contraction have a significant effect on long straight runs of conduit or pipe.
Once you get it buried, the temperature will be fairly stable, and the movement will be minimized. What are the specs on the pipe you are using?
For example, the coefficient of thermal expansion for PVC (3.38 x 10-5 in./in./°F) is almost three times as high as for aluminum and six times as high as for steel. Thermal expansion and contraction have a significant effect on long straight runs of conduit or pipe.
Once you get it buried, the temperature will be fairly stable, and the movement will be minimized. What are the specs on the pipe you are using?
chim
Elite Member
Neat project. Some time back I remember looking at the NEC for PVC expansion fitting requirements. For a location with a 100° swing (conservative for some locations between Winter and Summer) you'd need an expansion fitting in each stick of pipe. Burying the pipe might help.
I've been involved in some piping systems where the changes in the length of the pipe due to temperature change required anchors and guides in addition to the expansion fittings to ensure the movement happened where it should. Expansion loops were installed in some piping systems as well.
An excavating contractor once told me he dug a trench for a farmer for a water line to an outbuilding. They used a coil of black poly pipe that had been laying in the sun. The farmer did the connections and they backfilled the trench. The pipe contracted as it cooled and ripped both ends loose.
I've been involved in some piping systems where the changes in the length of the pipe due to temperature change required anchors and guides in addition to the expansion fittings to ensure the movement happened where it should. Expansion loops were installed in some piping systems as well.
An excavating contractor once told me he dug a trench for a farmer for a water line to an outbuilding. They used a coil of black poly pipe that had been laying in the sun. The farmer did the connections and they backfilled the trench. The pipe contracted as it cooled and ripped both ends loose.
EddieWalker
Epic Contributor
Looking at your pictures, the first thing that jumps out at me is the lack of purple primer. PVC pipe needs to have the purple primer to soften it so the clear cement will melt the two pieces together. When this is done, the joint is stronger then the pipe, and all your breaks will happen in the pipe, or at a T.
All the different colors and types of glues are pretty much worthless when dealing with PVC under pressure. They work OK for gravity lines, but even then, where I live, you will not pass an inspection if your drain lines do not have purple primer showing at each joint.
Here in East Texas, all water lines that have a decent amount of run will be slip jointed and not glued together. When the soil is wet and it freezes, it moves. When it thaws, it moves. The pipe needs to be able to slide in and out of itself so it doesn't break.
Since your line isn't under any significant pressure, you can probably get away with just a couple of slip joints. I've never worked with 8 inch pipe, but I'm sure that there are slip joints available for it since it's a common sized pipe used for city supply lines.
If it leaks now, it will only get worse if it's buried.
All the different colors and types of glues are pretty much worthless when dealing with PVC under pressure. They work OK for gravity lines, but even then, where I live, you will not pass an inspection if your drain lines do not have purple primer showing at each joint.
Here in East Texas, all water lines that have a decent amount of run will be slip jointed and not glued together. When the soil is wet and it freezes, it moves. When it thaws, it moves. The pipe needs to be able to slide in and out of itself so it doesn't break.
Since your line isn't under any significant pressure, you can probably get away with just a couple of slip joints. I've never worked with 8 inch pipe, but I'm sure that there are slip joints available for it since it's a common sized pipe used for city supply lines.
If it leaks now, it will only get worse if it's buried.