Tee
You have not stated what material you are using....
This is a Ford vs Chevrolet deal here. I believe you are splittings hairs. Pneumatic convey systems should not be designed with this close of tolerance. One plug and all savings are gone,
Have seen tee's in the plastic industry. This is done mostly due to cost-they are cheap. Stick with the sweeps. If you wish, we could test the difference on our equipment in our test facility.
regards, Peter Hoefler ■
"Blind Tee"
It is quite unfortunate that someone would ever try to convince an unknowing person, that a "blind tee" has a lower pressure drop than a long radius bend. A long radius bend would be defined, as a bend with a radius larger than 12 times the pipe diameter.
It is without question, that a long radius bend has a lower pressure drop than a blind tee or a short radius bend. In fact, we have done significant
tests at Dynamic Air Inc and have proved that the longer radius becomes, the
lower the pressure drops results. There is a direct relationship between
the bend radius and the pressure drop. One simple test is to simply measure
the resistance through the pipe, using lower pressure compressed air or a
liquid. One finds very quickly a short radius or blind tee has a very high pressure drop, as compared to a long radius bend.
I have heard of one particular manufacturer of short radius bends, who has
made the claim that a short radius bend or blind tee has a lower pressure
drop than a long radius bend. It is unfortunate, someone has not made this
manufacturer prove this ridiculous claim, because it is against all sound
engineering principles.
In my opinion, any manufacturer who makes this claim, just wants to sell
his product at any cost and thus falsely makes this claim! Irrespective of
the application as to if the application is moving air, solids, air and
solids or just liquid, the fact remains the longer radius bend is always a
better situation. You can also verify these statements, by using standard
available computer software, where the pressure drop through a bend can be
calculated.
A short radius bend has installation and cost advantageous and this is
primarily why engineers sometimes use short radius bends. If this false claim of lower pressure drops were true for blind tees and short radius bends, you would hardly ever see a long radius bend, because the blind tees and short radius are less expensive. However this exactly why one sees long radius bends, because they have performance advantageous not avail with the blind tees.
Regards,
James R. Steele
President
Dynamic Air, Inc.
Tel: (651) 486-3000
Jim.Steele@Dynamicair.com ■
Blind Tee
No a blind tee does not have a lower pressure drop than a long radius bend. I would be curious to know if any established pneumatic conveying company would claim it did. ■
Re: Blind Tee
Thank you all for your comments.
Regards
Pål G ■
Pressure Drop In Bends
Please e-mail me your full postal addess. We have undertaken much research work on the effect of bend radius and would be happy to post a couple of papers covering our results to you!
You would usually find a blind tee being used in applications where the conveyed material is highly abrasive and the increase in pressure drop in the system (from the use of blind tees) - hence operational overheads can be justified. Some aggregate handling plants use simple drum type bends which operate on the same principle as blind tees - i.e. fill with the conveyed material and provide a material on material impact region within the bend.
Hope this helps in some way!
Regards
Richard Farnish
The Wolfson Centre for Bulk Solids Handling Technology, Univ.Greenwich, London, UK
http://www.bulksolids.com
mailto: r.j.farnish@gre.ac.uk ■
Re: " Blind Tee"
I've just finished an extensive literature survey on the effects that various bends have on flow characteristics and all of the articles agree with the comments made above. A blind tee does not result in a lower pressure drop. However, if the conveyed particles are very abrasive, the use of a blinded tee can result in least particle attrition/equipment wear. It is closely followed by short radius elbow bends and the long radius bend causes the most equipment and particle damage. This is believed to be due to the conveyed materials filling out the pocket of blinded tee bends, dampening the impact of the particle/wall collisions. Similar results can however be obtained by using a flexible material for the bend or using drum bend.
Regards,
Smeeta ■
Re: " Blind Tee"
If flexible (by which I presume you mean rubber of uhmw-pe) materials are applied to impact regions it is important to be aware that you will only get acceptable wear life if the impact angle with the conveyed material is high (i.e. 90 degrees). Once the impact angles become much lower (say 10 degrees less) the rate of material loss from the lining material will accelerate. Conversely, the use of traditionally hard materials (i.e. basalt,etc) which tend to be brittle and hence tend to be less suitable for high impact angles - but better for lower impact angles. Again, papers dealing with this issue are available from The University of Greenwich.
Regards
Richard
The Wolfson Centre for Bulk Solids Handling Technology, Univ. Greenwich, London.
mailto: r.j.farnish@gre.ac.uk
http://www.bulksolids.com ■
"Blind Tee"
Hi Pal G,
I have been involved with pneumatic conveying of plastic pellets for more than 10 years. I have also been told that Blind Tees can reduce pressure drops, and have read reports of on-line tests proving this. I have also conducted tests, but found no reduction. I honestly did not expect this, but needed to prove my doubts to my colleaques. However, in all of the tests, in pipelines ranging from 50mm ID to 200mm ID at pressures of 45 kPa for the smaller bore, to 2,5 Bar for the larger bore, there was also very little increase in pressure. Normal good design should easily allow for this slight difference.
I have installed Blind Tees on my plant, but this was due to abrasion of the pipeline. In one instance I needed to replace a long radius ( 8 and 12 times Diameter) bend on a 76 mm line every 4 to 6 months. The Tee has now been in for more than a year.
Hope this helps,
Dave. ■
Re: " Blind Tee"
If you look for elbows which resolve at the same moment the problems of loss of load and abrasion, I can inform you about a patented system of an average beam of curvature (between 8 in 12 times the nominal diameter), which reduces the losses of load by variations of sections provoking a venturi effect and which prevents the abrasion because of an immobilization of material in internal traps in the elbow, the booby-trapped material serving as materials anti-abrasion. Communicate I your address so that I inform you on this product. ■
Re: " Blind Tee"
I have used both long radius bends and pocket tees and have not found much of a difference in the total pressure drop. For some materials pocket tees showed a lower pressure drop but not much.
Regards,
Amrit Agarwal
Pneumatic Conveying Consultants ■
Re: " Blind Tee"
My experience is taht if the convey system is working with in the pressure of the motive force, then blind Tees are quite good to use and do not add much pressure drop.
I have also had a system where we took out the blind tees from a system replaced them withlong radus bends and we were able to increase capacity of the system due to the pressure drop system. ■
Blind Tee
Dear friends.
of course the topic is not an easy one , I have used long raduis bends , very lon radius bends 19,mt , short radius bends and blind tees.
Blind tees do not always mean more pressure drop. if you are runing at vey low phase densities, the pocket will not fill, and you might have more pressure drop, if your material is sticky you might have a problem with tee bends and with long radius too, and you might need elastic bends , wheder tees or radius.
I did some extensive work in this field for 8 years and found that there was little pressure drop difference between long radius and tee bends, we had no choice but to use tee bends in my case x bends because of abrasion as you we dis consulted the experts at the time and got , as you mixed responses.
My material was a mixture of particle sizes from 2 inches to fine dust, we run dense phase and diluted phase in a 4 inch diameter 160+ mt long rigg. Rising 45 mt with iron ore. usoing air , nitrogen, hidrogen, CO 2 and CO as conveying media loadings from 1 to 20 tons per hr. had no problem with tee bends. Long and short radius were perforated in less than a day.
Hope this helps.
Marco Flores ■
Blind Tee
There have been a number of studies done on the difference in lines losses due to blind tees, and long radius sweeps and from what I've seen a blind tee doesn't reduce the losses in a system. Where I've used blind tees is for abrasive applications where cross contamination isn't a problem or where there just isn't the space to put a long radius elbow or sweep in. Of course a system should never be designed where its performance is so borderline that the style of turn will make or break the system.
Allen Powell ■
Re: " Blind Tee"
The key to pressure drop is where it is measured. If the test points are just before and just after the elbow - larger radius will show least pressure drop. How ever, to measure true drop one must take the downstream reading some distance from the elbow (after the material has had time to reaccelerate in the air stream.) This work results in addtional pressure drop.
Extensive tests have shown the minimum total pressure drop is lowest at a pipe radius of 2.5 to 3 times pipe diameter. Normally blind tees are made at 1.5 times pipe diam. so drop is not minimal.
A US manufacturer make a "special design blind T" that is at the optimal radius and has a built in bulb similar to a T that minimizes the wear due to holding material being transported.
If material being conveyed is not abrasive, I buy a standard 4 times diam radius sched 40 elbow and call it good.
Info comes from class taken from Paul Solte, pneum convey guru who writes many articles for Powder and Bulk Engineering magazine ■
Re: " Blind Tee"
Do not do it until you have someone review your system that dosnt sell them. Putting them back to back, to close to the pickup point etc is a REAL Problem.
Do some research before you even consider it. ■
" Blind tee"
I have been recommended a special type of bend called “blind tee”. I have been told this one gives less pressure drop than conventional bends (with “long radius”)
Do anyone have experience using those? And is it true that they reduce pressure drop?
Pål G ■