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Thread: The Generic 2HP DC
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12th June 2013, 12:11 AM #31.
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13th June 2013, 04:28 PM #32GOLD MEMBER
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13th June 2013, 06:08 PM #33.
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14th June 2013, 07:15 AM #34
Bob,
I think I speak for many when I thank you for sharing your efforts, knowledge and research with us. You provide an extremely detailed and precisely documented record for those (like myself) that are new to the complexities of efficient dust collection and how to best combat and/or maximise the existing downfalls of the required hardware currently available to consumers.
I personally am still trying to digest the mass of information you are constantly bombarding us with, and hope to soon be able to contribute to your threads in a constructive and meaningful manner. Until then, I can assure you that your efforts are well appreciated and are providing a steep learning curve to us mere mortals.
Please keep up the good work, and rest assured that any shortfall of forthcoming questions are due to a lack of understanding, and not due to a lack of wanting to engage with you in discussion on this fascinating topic.
Craig.
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14th June 2013, 11:06 AM #35.
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Cheers guys, much appreciated.
Yesterday I played around with an old small squirrel cage fan that I scavenged from a dumpster at work.
It was used to extract air from a small fume hood and uses a 1/4 HP, 1440 RPM, 3 Phase motor and an 8" squirrel cage impeller with 6" inlet and outlet ports.
The unit is over 40 years old and built like a brick outhouse from sturdy 6 mm thick PVC and steel plate.
The fan is attached to a 19 mm shaft that runs on two chunky pillow block bearings to a twin belt pulley and then there are two V-belts between the shaft and motor pulleys.
The whole thing was covered is gunk and the motor badly corroded, so I washed everything down and temporarily replaced the motor with a single phase 1HP 1440 RPM motor so I could test the flow.
As expected the pressure generated by this is very low and was only 0.5" of WC.
The expected flow from a 6" inlet/outlet is 250 cfm and I measured 240 cfm, ie useless for a DC or venting fan of any kind.
I will probably end up stripping it down for parts.
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14th June 2013, 11:58 AM #36... and this too shall pass away ...
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29th June 2013, 09:18 PM #37.
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Today I went to visit Jonno2000 and measured the flow on his new modified 2HP DC (see his mod in this post).
Johhnos static pressure was 8.6" of H2O Pressure which is 6% better than mine (@8.1").
The 6% difference could be due to slight differences in the impeller location within the impeller housing or maybe mine still has a leak in it somewhere.
The spec on these machines is 8.0" so Jonno's value means his system before the impeller is well sealed and will be a good reference value to use once his ducting is installed to check for leaks etc.
The flow rates came out as follows
Without any filters Jonno's DC has a flow rate of 1132 CFM (mine is 1112) which is consistent with his pressures being higher.
The 6% difference in pressure between the two DCs should result in an approximate increase in flow rate of about 3% but the increase in flow rate is only 1.7%.
This could be because mine has a Bell Mouth entry into the impeller whereas Jonno's uses a straight sided entry.
This difference of 20 CFM is marginal but could be worth exploring at a later date.
With the pleated filter (PF) Jonno's DC has a flow rate of 924 CFM whereas mine has 840 with the needlefelt bag.
So a PF seems to add about 10% to a DC flow rate over a Needlefelt bag.
This is a very positive result in terms of flow rate if it was not for the fact that the PF seemed to let through a surprising amount of dust - ie more than the needlefelt bag.
I do expect the PF will clog significantly and the filtering efficiency improve as it is used - the question is how much.
The PF was brand new as was the Needlefelt bag - what would be interesting is to measure the flow and efficiency as they get dirtier.
The PF should of course take much longer to clog and is much easier to clean with the internal paddle arrangement.
By looking at the pics you will see Jonno's is an H&F model and mine is of course a Timbecon unit.
The needlefelt bags suppiled are the "thinner" needle felt type, H&F rates theirs as a 5 micron bag, and I am pretty sure when I bought the Timbecon unit a few years back they rated theirs at 5 micron as well, but now looking at their website these bags are now rated at 15 microns . . . . . . .???
I am still calculating some filtering efficiency values and will report back when I have finished
Back to TOCLast edited by BobL; 5th March 2020 at 01:53 PM.
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29th July 2013, 02:12 PM #38Intermediate Member
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Hi Bob,
Thank you for the information. I am fairly new to woodworking and predominantly spend shed time on the lathe.
I am wanting to restrict my time in the shed until I can set up some form of extraction. I will need to compromise on the system as it is only a hobby and if I spend too much I will impact my ability to spend time in the shed.
- Would the Carba Tec 2hp (fm-300) be suitable for this mod?
- You mention that the system is not powerful enough to normally be located outside. If the ducting is fairly straight, what range would you consider reasonable from lathe to extractor?
- Is there benefit in changing the inlet to 6inch today but not changing the outlet yet? I will be moving house in the next few months so would prefer not to change too much yet as it wont be permanently fixed in place. I understand the full benefit arises with all 6 inch ducting.
Thanks for your help.
Cheers
Jarrad
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29th July 2013, 03:08 PM #39.
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Yes very suitable, have you seen Jonnos mod?
- You mention that the system is not powerful enough to normally be located outside. If the ducting is fairly straight, what range would you consider reasonable from lathe to extractor?.
A theoretical calculation for the modified DC is as follows.
The fully modified DC using bags has a flow of 840 CFM. Adding 6" ducting consisting of 2 long radius 90º bends, 3 m of pipe and 1 m of flex (ie just enough to get the ducting into a shed will get a flow of 762 CFM at the machine, adding the machine will drop that flow further depending on how throttled the machine is.
Extending the ducting by 6 m (e.g. to take it across the other side of a medium size shed) will drop the flow from 762 to 707 CFM, its not a BBQ stopper loss but, once again, seeing as the flow is already less than 1000 CFM the more you can retain the better.
Is there benefit in changing the inlet to 6inch today but not changing the outlet yet? I will be moving house in the next few months so would prefer not to change too much yet as it wont be permanently fixed in place. I understand the full benefit arises with all 6 inch ducting.
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29th July 2013, 04:12 PM #40.
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Pressure losses from flow rates for the 2HP DC
Having measured and calculated a few pressures and flows for the modified generic 2HP I thought I would plot these on a pressure/flow graph which makes it much easier to visualise and starts to show the fan curve for the modified DC.
The graph is for Flow rate versus pressure,
"Theory Max" is the theoretical maximum flow rate determined from an actual static pressure reading of 8.5 " of WC.
This is what some manufacturers measure and why the stated flow claim is 1200 CFM
"Actual Max" refers to a measured flow and the corresponding theoretical pressure determined from the flow.
This means the naked impeller provides a self resistance equivalent of 1" of WC.
"with PF" refers to "with pleated filter" and is a measured flow and a theoretical pressure. This indicates a loss of 2.3" of WC.
"With NF bag" is the same as previous but "with needle felt bag"
The two points with labels [2 x 90º + Xm 6" duct + 1m F] refer to adding 2 90º bends, Xm of 6" ducting and 1m of flex.
These are theoretical flow rates based on pressure losses using Bill Pentz "static calc" pressure/flow spreadsheet.
After all of the above the machines have to be added
The direction of the graph towards the LHS is not quite correct.
The trend of the graph must go smoothly through zero so the flows for the left most two points are clearly too high.
The reason for this is that both the pressures and calculated flows for these two points are both theoretical but they will still provide an indication of what is going on.
Back to TOCLast edited by BobL; 5th March 2020 at 01:57 PM.
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1st August 2013, 10:06 AM #41Member
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Bob, with the deepest of respect, I believe that your fan curve below is not drawn correctly.
Fan curves typically follow a descending line from left to right (google images “centrifugal fan curve”) demonstrating how our fans produce their maximum flow when there is the least pressure or restriction to flow and their maximum pressure when there is no flow.
It also shows how one must always take manufacturer’s claims with a grain of salt. They may claim 1200cfm and 8.5” pressure, but what is really meant is 1200cfm or 8.5” pressure, you don’t get them both at the same time.
Incidentally, I also have a theory which possibly explains some of the difference between the manufacturer’s claimed performance and what is actually measured. That is these dusties are typically developed in the US and tested with electric motors powered by 60Hz domestic supply typically running at around 3450 RPM. These performance figures are then used universally wherever the unit is sold or if remanufactured by some other player without further testing. When these machines are sold on our market with 50Hz motors running at around 2850 RPM a corresponding drop in performance is noted. Anyone with a Clervue cyclone or similar with VFD control will know the difference in performance between 50Hz and 60Hz.
Bob, hope you don’t mind, but I’ve taken the liberty to add a few marks to your graph to demonstrate my point.
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1st August 2013, 10:45 AM #42.
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You are absolutely correct, - what I have shown is a sort of inverse fan curve.
What I was really focussing on was the actual loss of flow from adding "stuff" to a system. My experience is that most wood workers attach lengths of 4" ducting and flexies to an already choked DC and then just stick their hands in front of the inlet and think "well that does not seem to have slowed the flow much" so they add a bit more, and then a bit more again, and then wonder why the inside of their shed eventually becomes covered in dust.
Incidentally, I also have a theory which possibly explains some of the difference between the manufacturer’s claimed performance and what is actually measured. That is these dusties are typically developed in the US and tested with electric motors powered by 60Hz domestic supply typically running at around 3450 RPM. These performance figures are then used universally wherever the unit is sold or if remanufactured by some other player without further testing. When these machines are sold on our market with 50Hz motors running at around 2850 RPM a corresponding drop in performance is noted. Anyone with a Clervue cyclone or similar with VFD control will know the difference in performance between 50Hz and 60Hz.
The 20% difference in rotational speed between 50 and 60 Hz translates to a 20% difference in flow rate. The other 30% comes about by the way the flow is measured and the fact that only naked impellers (ie no filters/bags or inlet/outlet constrictions) are measured.
Bob, hope you don’t mind, but I’ve taken the liberty to add a few marks to your graph to demonstrate my point.
Some day I will measure a real fan curve for the modified 2HP DC and post it. Mean while it has gone back to the milling yard to earn its keep.
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7th August 2013, 03:48 PM #43Intermediate Member
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Hi Bob, great post. I intend to do this same thing to my new TTI 2hp DC. It has the same specs as yours, i.e. 7.7amp rated motor with 2x94mm inlets. The intake behind the 2x94mm Y adaptor is 125mm OD which I would need to replace with a timber plate and 150mm ID port.
I am always wary of modifying equipment and want to make sure Im not going to overheat the motor and cause a fire. I have ordered a cheap clamp meter so will be able to measure current but is the 7.7amp really the operating capacity or is it intended as the startup max draw?
Kind regards
Karl
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7th August 2013, 05:47 PM #44.
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I have no idea what the 7.7 A refers to.
It cannot be the start up currents because they shoot up to ~ 35A on start up and take a few seconds to come down below 10A but I have never seen it go above about 6A when free running.
Sometimes I think they just make these numbers up.
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7th August 2013, 06:23 PM #45Intermediate Member
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