Pump

[Bill Shields]

VERY OUT OF DATE.....but then I have always considered myself to be little more than a high-tech blacksmith or a REALLY ADVANCED dinosaur

[Steve Bratina]

Don't we compress water to do a hydrostatic test?

[Builder01]

Don't we compress water to do a hydrostatic test?

I think the elasticity you see on a pressure gauge as you "pump up" a boiler during a hyrdo test, is probably due to the metal of the boiler moving slightly, more than the water actually compressing. Just a guess.

David

[Bill Shields]

also leaks and air bubbles.....

[Steve Bratina]

Leaks? The pressure increases with leaks? My full size HRT boiler needed a lot of pumping to get the pressure to 10% above MAWP. While the volume of the pump was small, water still went in but didn't leak out.
If you have a perfect container with no plate deflection or leaks that is FULL of water and you add one drop of water to the contents of the container, does the pressure inside rise a little, does it rise several pounds, or does it burst the container?
Darned if I know.

[DianneB]

I have done hydrostatic tests for many boilers and other pressure vessels and even a large boiler, if all the air is out, the pressure will rise very suddenly with the smallest amount of additional water.

[Bill Shields]

unless you put in a LOT of pressure...giggle.....

[Harold_V]

Boilers are made of elastic materials, so they stretch. Assuming all air is removed from the water contained within, the pressure is the result of the minor stretch of the entire boiler, as water does not compress. It will continue to stretch as more water is injected, assuming one has the ability to do so, until the weakest feature fails. The pressure rise is very fast in that condition, and the amount of movement (stretch) of the boiler is very small.

H

[Bill Shields]

Never knew that.....

[Builder01]

Bill, is that your loco? You just would not listen!

David

[NP317]

That photo: Must be an Italian locomotive... What's for dinner?

Boiler lengthening and stretching:
While firing up full sized logging steam locomotives from cold, I could see the rear of the boiler move aft about 3/8" to 1/2" during steam pressure increase from zero to 200 psi.
This was from both heat and pressure expansion. This is normal and expected.
And the reason to have flexible stay bolts in certain areas of the structure.
And why the boiler can slide on the rear frame.
And why long piping runs (like the injector delivery line) require expansion bends.

This stretching was also evident during hydrostatic pressure tests, although less, because of lower heat in the system.
Less heat means less expansion of the metals.
So... Boilers can stretch, while water does not compress, at the pressures we deal with in our boilers.
~RN

[Bill Shields]

nah....never put that many flues in ANY boiler I have built

it's interesting to LOOK at that picture and imagine exactly HOW all that spaghetti ended up in that configuration