Calculating Line/Pressure Loss Across Expansion Joints
Calculating Line/Pressure Loss Across Expansion Joints
(OP)
Guys & Gals --
Does anyone know how to calculate the pressure drop across an expansion joint? Or, what kind of pressure losses and/or K (Cv) values can one expect from an expansion joint? Lets say for water at any condition. I have checked with several manufactures, and they don't seem to test for this property....
Does anyone know how to calculate the pressure drop across an expansion joint? Or, what kind of pressure losses and/or K (Cv) values can one expect from an expansion joint? Lets say for water at any condition. I have checked with several manufactures, and they don't seem to test for this property....





RE: Calculating Line/Pressure Loss Across Expansion Joints
The more you learn, the less you are certain of.
RE: Calculating Line/Pressure Loss Across Expansion Joints
RE: Calculating Line/Pressure Loss Across Expansion Joints
Some expansion joints are lined and so the loss will be small. Other joints may have corrugated inners and create a higher loss.
If the question was for flexible air ductwork hose, the PD is about 2 or 3 x the rate of standard ducting (for corrugated compared to straight).
Friar Tuck of Sherwood
RE: Calculating Line/Pressure Loss Across Expansion Joints
In many types of duct and piping EJ's, there is a flow liner built into the joint to protect the convolutions (metal) or material (fabric) of the joints.
Flow distrubances that would contribute to pressure drop in the system would be specifically related to the protrusion (or not) of the flow liner into the flow stream.
Joints with no flow liners, now, that is another matter.
rmw
RE: Calculating Line/Pressure Loss Across Expansion Joints
RE: Calculating Line/Pressure Loss Across Expansion Joints
thanks
RE: Calculating Line/Pressure Loss Across Expansion Joints
The reference “Idelchik, I. E., 1986, Handbook of Hydraulic Resistance, Second Edition, Hemisphere Publishing Corporation, New York (1986)” is the ultimate source for obscure loss coefficients.
Page 462 of Idelchik has loss coefficient for expansion joints. The loss coefficient depends on the type and size of expansion joint. I can e-mail you the page from Idelchik that discusses expansion joints. Please contact me at Elicson@fauske.com.
For bellows type expansion joints, Idelchik reports K=1.7 for 50 mm diameter bellows up to K=2.3 for a 500 mm diameter bellows.
Hope this helps.
RE: Calculating Line/Pressure Loss Across Expansion Joints
I'm looking for the k values for friction loss thru' expansion bellows for a 150mm and 200 mm ID pipe. Please could you help. Will try to get a hold of this handy reference
RE: Calculating Line/Pressure Loss Across Expansion Joints
I would appreciate it if anyone who I e-mailed the reference to could e-mail a copy of it back to me at elicson@fauske.com.
Thank you.
TREMOLO
RE: Calculating Line/Pressure Loss Across Expansion Joints
RE: Calculating Line/Pressure Loss Across Expansion Joints
As I recall, the loss coefficient increased monotonically with increasing pipe diameter. So, interpolation should give you a reasonable estimate.
This is what I get for trying to store everything electronically and eliminate paper from my office. I've failed on both accounts - my electronic files are inaccessible and my office is still overflowing with paper.
TREMOLO
RE: Calculating Line/Pressure Loss Across Expansion Joints
Input:
Minimum ID (ID) (inches)
Length (L) (inches)
Number of corregations per inch (N)
Roughness factor (e)
Output:
Fully Turbulent Friction Factor (f) = 1/(4*(0.57-LOG(12*e/ID))^2)
Equivalent Length = L*N*ID/f*(1-(ID/(ID+0.438/N))^2)^2
You should find the equivalent length of a section of convoluted bellow is generally between 8 and 12 times the actual length.
RE: Calculating Line/Pressure Loss Across Expansion Joints
RE: Calculating Line/Pressure Loss Across Expansion Joints
A bit of algebra converts the equivalent length formula to one for the friction factor for the corrugated hose:
f=N*ID/{1-[ID/(ID+.438/N)]^2}^2
If this formula is correct using the height of the corrugations as the roughness hieght in the Moody diagram, as sailoday28 suggests, overestimates the friction by a factor of 2 (at least for the 6" size that I'm interested in).