"Ten diameters" of pipe upstream of a flow meter?
"Ten diameters" of pipe upstream of a flow meter?
(OP)
There's a rule of thumb that says a flow meter requires ten diameters of straight pipe upstream, and five diameters of straight pipe downstream in order to provide "clean" flow at the meters inlet/outlet. This rule is often printed explicitly in the installation manuals for commercially produced flow meters.
Question: will these lengths of straight pipe permit me to do whatever I want to the flow at positions further upstream/downstream of those limits? Or are these lengths only intended to cope with the typical minor flow perturbations introduced by simple elbows and/or manifolds?
Question: will these lengths of straight pipe permit me to do whatever I want to the flow at positions further upstream/downstream of those limits? Or are these lengths only intended to cope with the typical minor flow perturbations introduced by simple elbows and/or manifolds?





RE: "Ten diameters" of pipe upstream of a flow meter?
If yes, there is no problem as the recommendation of 10/5 is only to ensure steady flow before / after the measuring point.
It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)
RE: "Ten diameters" of pipe upstream of a flow meter?
>at a greater distance than 10/5 from a flow disturbance?
The specific case I'm thinking of is a flow meter with ten diameters of straight pipe upstream, with the upstream end of that pipe (the inlet) open to atmosphere. I'm wonder what sort of obstructions could be tolerated at that inlet while still providing clean flow to the meter.
RE: "Ten diameters" of pipe upstream of a flow meter?
So to answer your basic question, the code allows any piping configuration upstream of the straight pipe requirements.
I don't understand your second post. If the upstream end is open to the atmosphere, the only way you would have any flow is to pull a vacuum on the downstream end, and vacuum is one of the cases where the AGA equations are invalid.
David Simpson, PE
MuleShoe Engineering
In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. ùGalileo Galilei, Italian Physicist
RE: "Ten diameters" of pipe upstream of a flow meter?
It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)
RE: "Ten diameters" of pipe upstream of a flow meter?
OK, here's what I've got:
18" diameter duct. 180-inch-long straight section, upstream end open to atmosphere, downstream end connected to flow meter. Downstream of the meter, there is a 90-inch-long straight section, and then there's a blower, pulling air through the duct.
I'm wondering what sorts of obstructions can be tolerated near the inlet end of this system.
RE: "Ten diameters" of pipe upstream of a flow meter?
For your application, there are a number of unknowns:
- Pipe size
- Velocity
- Type of pipe entrance
- Type of flow meter
- Meter accuracy required
- Pipe orientation
- Air in fluid
The rule of thumb are minimum values, increasing these dimensions will often improve the flowmeter performance (accuracy). Where two or more disturbances are located upstream of the meter, the longest recommended upstream pipe run is to be observed as an absolute minimum. Wherever possible mount any control and butterfly shut off valves downstream of the flowmeter.RE: "Ten diameters" of pipe upstream of a flow meter?
Putting an orifice on the inlet of a blower is a bit off.
Just what level of accurracy are you after?
RE: "Ten diameters" of pipe upstream of a flow meter?
It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)
RE: "Ten diameters" of pipe upstream of a flow meter?
don't really understand why the meter is on that side of the blower - you're either going to introduce more losses in a system which doesn't have much to spare or result in lower flow velocities / bigger diameter meter, neither of which is normally good news.
Swirl, pulsation and vorticies are normally your enemies in this instance so reduce / eliminate those and you're going in the right direction.
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: "Ten diameters" of pipe upstream of a flow meter?
David Simpson, PE
MuleShoe Engineering
In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. ùGalileo Galilei, Italian Physicist
RE: "Ten diameters" of pipe upstream of a flow meter?
RE: "Ten diameters" of pipe upstream of a flow meter?
http://www.nyb.com/Catalog/Supplements/CS-491.pdf
RE: "Ten diameters" of pipe upstream of a flow meter?
The flow measurement device is a smooth-approach orifice. The throat is perhaps 7" in diameter (don't recall exactly), and the main duct is 18" in diameter.
The fluid is air.
Upstream of the SAO is 180" of straight pipe, 18" diameter, with the upstream end of that pipe open to atmosphere. No louvers, filters, or anything like that.
Downstream of the SAO is 90" of straight pipe, 18" in diameter, with the downstream end connected to a blower that pulls air through the whole system.
Flow velocities are on the order of 20 feet per second.
The issue is that there is a stationary object near the inlet end of the pipe. Perhaps a foot upstream, and flush with the outer edge of the pipe.
Question: is this object likely to cause flow perturbations that will persist all the way to the SAO and influence its accuracy, or can I count on the 10 diameters of pipe between the inlet and the SAO to produce axisymmetric flow at the SAO, regardless of what's happening at the inlet?
RE: "Ten diameters" of pipe upstream of a flow meter?
RE: "Ten diameters" of pipe upstream of a flow meter?
http://www2.emersonprocess.com/en-US/brands/rosemo...
You have abided the 10 diameters rule, but your flow accuracy won't be that good
RE: "Ten diameters" of pipe upstream of a flow meter?
http://www2.emersonprocess.com/en-US/brands/daniel...
[img = https://www.dropbox.com/s/r9mygqm70sm4hx5/OMG%20so...
RE: "Ten diameters" of pipe upstream of a flow meter?
RE: "Ten diameters" of pipe upstream of a flow meter?
"The minimum recommended length of unobstructed straight pipe varies from 13 to as much as 145 pipe diameters (internal pipe diameters) upstream of the orifice plate and 4.5 pipe diameters downstream of the orifice plate (Figure 8)."
http://asgmt.com/wp-content/uploads/pdf-docs/2009/...
RE: "Ten diameters" of pipe upstream of a flow meter?