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steel cylinder hydraulic test

steel cylinder hydraulic test

steel cylinder hydraulic test

(OP)
Hi all.
In a factory in Portugal we are testing (with water) the steel cylinder for the production of concrete pressure pipes diam. ID 500 till 1600 mm (AWWA C301). The cylinder is a steel pipe with very thin wall (2 or 2.5 mm) and completed with steel spigot and socket rings for rubber sealing. When the test is performed (in average the test pressure is 4 - 5 kg/cm2), the cylinder has to be emptied (by a pump) and simoultaneously water has to be replaced by air to avoid vacuum : if not the cylinder will shrink immediately like paper.
How it is possible to calculate the vacuum, knowing of course the pump caracteristics ?
And how to calculate the air delivery (from tank at 8 kg/cm2) to avoid vacuum or at least the buckling disaster ?
At present said procedure is performed manually, but we want to speed up because the operation is a bottle neck.
Attached photos of prototype machine
Thanks

RE: steel cylinder hydraulic test

No need to calculate the vacuum, since you do not want any vacuum to form at all, ever!
Size the air inlet valve, using a full port ball valve, to have the same port diameter as the pump's discharge line's inside diameter. Air flow capacity through such a valve, as long as attaching pipe remains short, will be greater than the water flow capacity through the discharge pipe. If it is sized using that simple method, no vacuum will be possible to form thereby keeping the pipe safe.

I hate Windowz 8!!!!

RE: steel cylinder hydraulic test

Why remove the water with a pump? Just use compressed air to force the water out.

Ted

RE: steel cylinder hydraulic test

(OP)
hi HYDTOOLS

because the air pressure (8 kg/cm2) is higher than the hydraulic testy pressure (4 - 5 kg/cm2)

thanks to all

Regards

RE: steel cylinder hydraulic test

I agree with hydro tools - Why don't you just install an air regulator and relief valve?? sounds like a much better plan than the risk of vacuum collapse which I imagine would occur with very little negative pressure.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

RE: steel cylinder hydraulic test

That doesn't make sense unless your pipe from the pump is small or very long or both as the maximum head into the pump can only be 1m assuming your air inlet is just open to atmosphere. with 2 bar air it would be a lot more.

you could always put in 2 bar air as well as the pump....

How does it work now?

I don't think anyone really answered your original question which is basically you need to add air at the same volumetric rate in standard terms as the pump outflow rate. There are many equations on how to calculate pressure difference across an air intake given the flow rate and density (atmospheric conditions). Big Inch probably has it right, i.e. make your air inlet as big if not bigger than your water outlet nozzle. If you add pressurised air at say 2 bar it would go even faster.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

RE: steel cylinder hydraulic test

(OP)
Thanks, LittleInch
I will report your suggestions (they sound very simple and easy to modify on the machine)

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