How does water pressure change as heat is applied to the pipe?

Question

I have 4" ductile iron pipe and it is not holding constant pressure, however, the pipe is exposed and so the heat fluctuates during the day and the pressure changes, what is going on?

Answer 1

Pressure and temperature are proportional to each other. Raise the heat, and you raise the temp. Likewise, you raise the pressure, you will also increase the heat in the fluid.

What kind of pressure/temps are we talking here.....??

Answer 2

If you are sure it is just the changes in temperature that is causing the pressure changes then it is almost certainly due to thermal expansion.

As the temperature of the pipe and water increases their volumes will increase as materials tend to expand when heated and as they cool the opposite happens they will tend to shrink. This will affect the pressure but not by much I would expect.

Why not try insulating (lagging) the exposed pipe to try and reduce the temperature changes  

Answer 3

You will probably find that due to the thermal expansion of steel your pipe is becoming larger and longer as it becomes hot.