Using air to increase pressure in Hydrostatic test
Using air to increase pressure in Hydrostatic test
(OP)
hello all,
I would like to know if filling a hose with water and then adding air on top of the water to increase pressure would work. I believe its the same theory as a air over hydraulic pump which can get 100 psi of air pressure to create 10,000 psi of oil pressure.
I attached a very professional photo
of the basic idea.
1. open water supply and opposite end of hose until it is completely full with no air in the hose.
2. close opposite end and then water supply.
3. open air supply until water pressure increases to desired test pressure.
4. stop air supply. release pressure at opposite end of hose.
Would this work? Any links, standards, procedures, examples, special equipment, anything at all would be fantastic.
Thanks for reading!!
I would like to know if filling a hose with water and then adding air on top of the water to increase pressure would work. I believe its the same theory as a air over hydraulic pump which can get 100 psi of air pressure to create 10,000 psi of oil pressure.
I attached a very professional photo
of the basic idea.1. open water supply and opposite end of hose until it is completely full with no air in the hose.
2. close opposite end and then water supply.
3. open air supply until water pressure increases to desired test pressure.
4. stop air supply. release pressure at opposite end of hose.
Would this work? Any links, standards, procedures, examples, special equipment, anything at all would be fantastic.
Thanks for reading!!





RE: Using air to increase pressure in Hydrostatic test
The water pressure I want to get to is only 525 psi.
RE: Using air to increase pressure in Hydrostatic test
RE: Using air to increase pressure in Hydrostatic test
The tricks are: (1) the piping on the small side of the piston must be completely full of liquid and mostly not compressible; (2) the seal between the two ends of the piston must be nearly perfect; and (3)there must be enough travel in the piston to handle the small compressibility that you do have.
Just pumping air into a water line will just turn the test into a pneumatic test and you will have to add enough air to get to your test pressure without any multiplier effect at all.
David Simpson, PE
MuleShoe Engineering
"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
RE: Using air to increase pressure in Hydrostatic test
RE: Using air to increase pressure in Hydrostatic test
So, the air would push it's way through the water into the hose?
RE: Using air to increase pressure in Hydrostatic test
RE: Using air to increase pressure in Hydrostatic test
The 2nd problem is that the pressurized gas contains a lot more explosive potential than water, and so is more dangerous. Even if the air pocket is small, the gas dissolved into the water can un-dissolve very rapidly, giving a lot more "boom" when a pipe or fitting ruptures.
RE: Using air to increase pressure in Hydrostatic test
Good luck,
Latexman
RE: Using air to increase pressure in Hydrostatic test
Air will dissolve in the water which will tend to lower the pressure reading during the testing time.
It is too dangerous to hydrotest with air pressure. Most air pressure tests limit the air pressure to approximately 20 psi or less.
Unlike water, which is incompressible, air is very compressible, making it hydraulically equivalent to a large mechanical spring. If something were to break or come free during a high pressure air test, the released air could propel an object a great distance with much force. This is why the necessary elimination of trapped air when initially filling pipelines can be so hazardous; air tries to move things to relieve built up pressure; water, because it is incompressible, does not.
http://www.ejprescott.com/media/reference/PresTestwAirvsWaterR-25.pdf
RE: Using air to increase pressure in Hydrostatic test
The test will be greatly less sensitive to leakage than a test where water is used as the pressurizing medium IF a pressure gauge is used as the means of detecting leakage. The gas pad will dampen pressure losses due to small liquid leaks, and as mentioned will also tend to dissolve (slowly) into the water.
This sort of test is nowhere nearly as dangerous as a full pneumatic test, contrary to what some people have stated above. The hazard of such a test is proportional to the volume of stored gas at a given pressure, which should be small unless the vessel under test is quite large, the test pressure very high and/or the item under test is very elastic- I don't know the nature of your hose, but that might be a problem in your case.
As to pressure multiplication, you have the answer above: you need two diaphragms or pistons of different areas, coupled by a rigid shaft. You only need a pump if one stroke of the cylinder/diaphragm doesn't give you enough water, which is likely even if your hose is quite rigid.
RE: Using air to increase pressure in Hydrostatic test
http://www.irc.wisc.edu/pda.php?/file&id=328
RE: Using air to increase pressure in Hydrostatic test
Losing 0.5 psi from a hydrotest could just be due to temperature. Losing 0.5 psi from your pneumatic/hydro combo could represent enough liquid loss to be of concern. Visual inspection should catch it but you never know.
RE: Using air to increase pressure in Hydrostatic test
From a sensitivity perspective using pressure loss as the means of detecting leakage, I agree that a test performed this way is less sensitive than one performed with the unit certified liquid full by evacuating and then filling with water. However, most people who perform hydrotests are far less scrupulous than that, tending to leave trapped gas in nozzles etc. Those gas pads behave in exactly the same way as far as test sensitivity is concerned.
RE: Using air to increase pressure in Hydrostatic test
CoolDude003 posts that he is pressure testing a hose, not a vessel. Pressure testing of flexible hoses is different than pressure testing of rigid wall tanks. Unlike a vessel, a hose will stretch and release energy in a springlike fashion.
http://www.jgbhose.com/data_returns/testmethods.asp
CoolDude003 doesn't post whether this hose is 1-Inch or 500-Feet in length, nor does he post the diameter, materials, sevice life, pressure rating, or material of construction.
With the limited information posted, the best course of action is for CoolDude003 to take his hose to someone that does pressure tests for hire, rather than attempt this by himself.
Moltenmetal:
"Always use water for pressure testing."
See page 11.
http://www.gates.com/downloads/files/catalogs/IndHosePrevMainMan.pdf