Static pressure measurement and best methodology

[harryz8819]

I have few questions with regard to static pressure measurements:

I am trying to understand which is the best place to place a static pressure probe and how it is affected by eddies/turbulence , valves, pipe bends etc....links to papers / detailed explanations would be very helpful

Is it common to see static pressure bouncing around if is placed in eddies/regions of flow swirling ?

Are there good practices to measure accurate static pressure in pipe flow/ near valves ?

Looking forward to your answers....

Thanks,

 

[25362]

Thread403-6738 and more than 4000 others treat the subject of "static pressure". Try to activate Search at the top of this page to find them.

 

[LittleInch]

lots of variables so lots of solutions / issues

Best place for highest accuracy is in a long pipece of pipe with no flow distrurbances (elbows, valves, tees etc) within 5D min of the pressure tapping.

There are many things and codes written about where the tapping needs to be for orifice meters to get the required accuracy.

Does the term "probe" imply something entering the fluid? like a pitot tube?

If yuo put your PI immeadiately downstream of a control valve which is throttling and creating a lot of noise, turbulence and vapour bubbles the it will bounce around a bit, ditto d/s of a PD pump which doesn't have a multiple cylinders and a damper.

Otherwise valves should be open or closed so really no different to pipe, unless they leave something in the flow like a butterfly valve or swing check valve.

A lot depends on the accuracy you're trying to obtain and the purpose behind the reading, but in general try for simple straight bits of pipe.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[PEDARRIN2]

Isn't static pressure, by definition, taken when there is no flow?

If so, then eddies or turbulence are meaningless and location would be directly related to elevation.

Or am I missing something?

 

[LittleInch]

In theory at the pipe wall there is no flow and generally no flow along the tube connecting the main pipe to the pressure guage / transmitter.

However if the fluid itself is subject to pressure changes and fluctuations then the reading on the guage is not representative of the pressure in the fluid and I think that's what the OP is actually asking.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Latexman]

True PEDARRIN2. Most measurements I've seen are the static pressure of a flowing stream, which is an oxymoron, right? A tee of at least 5D length/elevation is recommended to keep the eddies near the T inlet away from the transmitter.

Good luck,
Latexman

To a ChE, the glass is always full - 1/2 air and 1/2 water.

 

[LittleInch]

Indeed you can make use of these issues to measure things - see

http://www.maxiflo.co.kr/English/Technology/flowmetertypes.htm

and scroll down to "elbow tap meters"

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[bimr]

Pressure is the amount of force exerted on a unit area. There are two kinds of pressures, the static pressure and dynamic pressure. Static pressure is the amount of pressure exerted by a non moving liquid due to gravity. When there is a container filled with water, there is a static pressure exerted by the water on the bottom of the container because of gravity.

Regarding: I am trying to understand which is the best place to place a static pressure probe and how it is affected by eddies/turbulence , valves, pipe bends etc....links to papers / detailed explanations would be very helpful

Is it common to see static pressure bouncing around if is placed in eddies/regions of flow swirling ?


You are observing the total pressure of the combined static pressure and dynamic pressure.

If a fluid is not moving (and open to atmospere), the measured pressure is the same in all directions is the static pressure. But if the fluid is moving, the measured pressure depends both on the static pressure and on the pressure caused by the energy of its motion, in the direction of that motion. The added pressure from the fluid's motion is called dynamic pressure.

If you want to measure the static pressure accurately, the fluid will have to be at rest.