Static pressure difference in different ID pipe tees?
Static pressure difference in different ID pipe tees?
(OP)
Can someone explain what kind of pressure difference I would expect to see on a gage on a pipe tee (1" NPT pipe size) if I had an original pipe tee ID of .815" and changed it to a lower pressure tee with a smaller wall thickness which makes the ID 1.160"?
The gage is located on the non straight through leg of the tee.
I know static pressure increases as pipe size increases and static pressure decreases as velocity increases... so is there a way to calculate the expected difference? is it directly proportional to size difference? thanks
The gage is located on the non straight through leg of the tee.
I know static pressure increases as pipe size increases and static pressure decreases as velocity increases... so is there a way to calculate the expected difference? is it directly proportional to size difference? thanks





RE: Static pressure difference in different ID pipe tees?
Dynamic pressure change is related to velocity difference, which can be related back to the difference in area. V2 = V1/A1*A2, pressure reduction would be (V2-V1)^2/2/g
Only put off until tomorrow what you are willing to die having left undone. - Pablo Picasso
RE: Static pressure difference in different ID pipe tees?
RE: Static pressure difference in different ID pipe tees?
Only put off until tomorrow what you are willing to die having left undone. - Pablo Picasso
RE: Static pressure difference in different ID pipe tees?
total pressure remains constant so when dynamic changes doesnt static have to adjust accordingly to some degree?
thanks for the help so far... I just need to connect the dots
RE: Static pressure difference in different ID pipe tees?
Ptotal = Pstatic + Pvelocity + Phead
ht
Good luck,
Latexman
RE: Static pressure difference in different ID pipe tees?
so if Pstatic1= 100psi and V1=3ft/sec and v2=2v1
then Pstatic2=86.5psi
am I missing something?
RE: Static pressure difference in different ID pipe tees?
http://ww
say @ 20°C = 1.205 kg/m3 = apx. 0.075 lbs/ft3
calculate stagnation pressure of 3 fps
= ρ*v2
= 0.075 pcf / 32.174 ft/s2 * (3 fps)2
= 0.00234 * v2
= 0.00234 * 3 2
= 0.0211 psf
psi
= 0.0211 / 144
pressure change at low velocities will be very very small
Only put off until tomorrow what you are willing to die having left undone. - Pablo Picasso
RE: Static pressure difference in different ID pipe tees?
Since there is no change in the flow conditions in the main 1-in pipe, why should there be a change of pressure readings?
RE: Static pressure difference in different ID pipe tees?
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RE: Static pressure difference in different ID pipe tees?
Only put off until tomorrow what you are willing to die having left undone. - Pablo Picasso
RE: Static pressure difference in different ID pipe tees?
The only change has been apparently done on a dead end pressure gage, therefore no change in flow conditions.
RE: Static pressure difference in different ID pipe tees?
If total energy is assumed to remain the same and flowrate is assumed to remain the same, density same ...
P1/den + V1^2/2/g = P2/den + V2^2/2/g
P2 = P1 + ((Q/A1)^2/2/g - (Q/A2)^2/2/g) * den
In any case, the dP caused by 3 fps dV isn't going to be noticable on my pressure gauge.
Only put off until tomorrow what you are willing to die having left undone. - Pablo Picasso
RE: Static pressure difference in different ID pipe tees?
second thing is I see where you got that density from on the chart but isnt the density at 100psi and lets say 70F is approx the temp in our shop = .585lb/cf which I get from the chart on the same website that relates air density to temp and pressure
If I use those numbers above for psi=density*(v^2) I get 3.22 psi for the larger dia and 13.24 psi for the smaller dia
I am also confused on what pressure the gage is reading... I thought pressure gages only read static pressure... so by figuring out the stagnation pressure are you figuring out what pressure to theroetically subtract from the total pressure to get what you would see on the gage? so in this case it would be approx 97 and 87 psi?
RE: Static pressure difference in different ID pipe tees?
density should be (gauge + atmos) psia divided by atmos
so if 100 is psig, then (100+14.73)/14.73 * 0.00234 = den2
Correct for temperature if you need to do so too.
I wasn't expecting 10 psi difference, is it really that much?
Only put off until tomorrow what you are willing to die having left undone. - Pablo Picasso
RE: Static pressure difference in different ID pipe tees?
0.075pcf /32.174 ft/s^2 * (14.73+100)/14.73 * (3fps)^2 = 0.163 psf
correcting mass density for 100 psiG
0.00233 slugs/ft3 * (14.73 + 100)/14.73 * (3fps)^2 = 0.163 psf
still looks pretty small.
Only put off until tomorrow what you are willing to die having left undone. - Pablo Picasso
RE: Static pressure difference in different ID pipe tees?
Doing calculations like this in customary units is almost a guaranteed way of getting the wrong answers, unless you are doing this on a daily basis and have the units and conversions at your fingertips.
The formula for velocity head is
h = v2/(2g)
where h is the head in feet of flowing fluid
v is the fluid velocity in ft/s
g is the earth's gravity
If you want the answer in pressure units you multiply by the fluid density and the earths gravity
P = ρv2/(2)
BUT if you still have the velocity in ft/s and the density in lb/ft3 then the pressure is in poundals per square ft
If you want P in psi you have to divide by gc to convert poundals to pounds force and by 144 to convert square ft to square inches
i.e. P = ρv2/(2*144*gc)
To get the difference between your two conditions, and assuming constant density
ΔP = ρ x ( v12 - v22) / (2*144*gc)
= 0.59 x (42.12 - 20.82) / (2 x 144 x 32.2)
= 0.085 psi
Katmar Software - Engineering & Risk Analysis Software
http://katmarsoftware.com
"An undefined problem has an infinite number of solutions"
RE: Static pressure difference in different ID pipe tees?
Only put off until tomorrow what you are willing to die having left undone. - Pablo Picasso