" 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?
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
Last edited by Peter Hoefler; 18th October 2002 at 17:05.
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
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
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.
James R. Steele
Dynamic Air, Inc.
Tel: (651) 486-3000
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.
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!
The Wolfson Centre for Bulk Solids Handling Technology, Univ.Greenwich, London, UK
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.
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.
The Wolfson Centre for Bulk Solids Handling Technology, Univ. Greenwich, London.
20th September 2002, 15:02
Principal Process Technologist
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,
4th October 2002, 18:40
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.
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