Pressure/Flow Fluctuatons of a nozzle

[karenbob]

Looking for some help in understanding what may be causing pressure/flow fluctations on a nozzle.
Details: The nozzle is basically a 1/4" tube about 3/4" long with one end capped. About 1/4' from the capped end are two orifices 180 degrees apart. The open end of the tube is subjected to calibrating fluid at 49 PSI. Flow from the orfices measures about 2.00 lbs/minute from each orifice. Fluid is at 85 degrees F.

Issue: Some nozzles exhibit a pressure fluctuation of about +/- 2 psi. This occurs at a rate of about 3 times per second. Flow is affected in the same way. Some nozzles exhibit this while others exhibit a contant flow and pressure. This is repeatable. Plumbing, pumps, etc. have been changed with not effect. We do not see anything different between the two types of nozzles.

Any thoughts as to the cause of this phenomina is appreciated

 

[Mordred]

The orifice size may be seeing small miniscule alterations in size due to weak springs,loose gaskets etc without knowing more about the nozzle and its type I'm only guessing here. The fact that some nozzles work correctly lead me to believe the problem is within the nozzle that is not working correctly bad seals etc.

 

[boneh3ad]

How do you cap the tube?

 

[256bits]

You really haven't explained your setup completely.
I assume your fluid is something like water

Are you testing one nozzle at a time, or do you have a string of nozzles on a run of tube being tested all at the same time, with some nozzles acting up and others not.

And how is the "calibrating fluid at 49 PS" generated and where is this pressure meter.

You say "Some nozzles exhibit a pressure fluctuation of about +/- 2 psi. This occurs at a rate of about 3 times per second. Flow is affected in the same way"
How did you determine the 2psi variation?

And are both orifices on a "bad" nozzle affected at the same time or alternately?

You obviously say you have some type of noticeable flow variation in certain nozzles.
1. The pressure valve you are using is sensitive to a certain pressure and flow and because the orfices are not all the same size, the "bad" nozzles will cause the pressure valve to oscillate at the frequency of 3 Hz you mention.
2. You have a vortex or eddy from a sharp bend or obstruction that causes a swing in pressure at the orifice. Perhaps the 2 orifices are misaligned from the 1/4 inch from the end of the nozzle tube, to cause a pressure variation to swing back and forth from orifice to orifice.
3. You have entrained air in the system. Perhaps a bubble has formed at the tip where the capped end is and acting to cause pressure variation.
4. Is there any chance of cavitation around a sharp corner, but that would be at a higher frequency I would bet.

 

[Mordred]

You really haven't explained your setup completely.
I assume your fluid is something like water

Are you testing one nozzle at a time, or do you have a string of nozzles on a run of tube being tested all at the same time, with some nozzles acting up and others not.

And how is the "calibrating fluid at 49 PS" generated and where is this pressure meter.

You say "Some nozzles exhibit a pressure fluctuation of about +/- 2 psi. This occurs at a rate of about 3 times per second. Flow is affected in the same way"
How did you determine the 2psi variation?

And are both orifices on a "bad" nozzle affected at the same time or alternately?

You obviously say you have some type of noticeable flow variation in certain nozzles.
1. The pressure valve you are using is sensitive to a certain pressure and flow and because the orfices are not all the same size, the "bad" nozzles will cause the pressure valve to oscillate at the frequency of 3 Hz you mention.
2. You have a vortex or eddy from a sharp bend or obstruction that causes a swing in pressure at the orifice. Perhaps the 2 orifices are misaligned from the 1/4 inch from the end of the nozzle tube, to cause a pressure variation to swing back and forth from orifice to orifice.
3. You have entrained air in the system. Perhaps a bubble has formed at the tip where the capped end is and acting to cause pressure variation.
4. Is there any chance of cavitation around a sharp corner, but that would be at a higher frequency I would bet.

I concure with this post explained in greater detail than i did LOL. We definately need more detail on the nozzle to further help you (even a part number that we can find a mechanical breakdown on the internet) would prove highly useful.