Hello,
I have a 1.5hp Charnwood w680 dust collector which is then connected to my cyclone seperator. This is via a 2.5m flexible hose from extract to cyclone it is 50mm diameter. The cyclone is connected to a 220litre plastic barrel with screw on airtight lid. The cyclone then feeds out to a 50mm 2.5m flexible hose which is then positioned near my lathe. Everytime I turn on the extractor the barrel starts to collapse under the pressure/ suction?? Any help? Is the cyclone too small or flexible hose to narrow?
Hi Moller,
I hope we haven't confused you with a blizzard of replies, dust collection seems to be a hot topic on this forum. To summarise some of the replies and add in some of my own observations to put it all in perspective.
You are right to assume the cause is due to the small cyclone with narrow flex hose leading from it, however the large barrel is also a bit weak so prone to collapse. As others have pointed out. the W680 is quite a powerful collector with a wide pipe (ca 4''?) so throttling down to 2'' at the cyclone will lead to a pressure drop in the cyclone and barrel causing it to collapse.
There are a number of solutions, in order of simplicity.
1. Fortify the barrel
The simplest is to fortify the barrel or replace it with a stronger and smaller tin one. That will probably do what you want.
2. wider pipes
Your narrow pipes reduce the efficiency of dust collection. Although the narrow pipes force the air to move faster, which is good if you want that kind of vacuum cleaner suck (fast air through narrow hole), overall there will be less air flow, as the air flowing in narrow pipe experiences a lot more drag from friction of the air over the narrow pipework. If you find you need more suck at your lathe then you may want to increase the pipe diameter to equal that of the W680 port and replace the cyclone with one with wider ports or buy something like this to turn your barrel into a Thein type cyclone
Cyclone Dust Collector Kit | Next Day Delivery
This is a much bigger change, so only worth doing if you need the extra suction.
3. Pressure relief valves
Lots of debate on the virtues of PRVs
A pressure relief value PRV is great for protecting against occasional one-off events, typically when a pipe gets blocked and will save a dust collector from imploding when that happens, it also relieves strain on the vacs motor (actually it protects from the motor overhearing - thanks DBT85). The vac could get blocked by shavings or inadvertently closing a blast gate etc the PRV opens and relives the pressure when an ABNORMAL EVENT occurs.
However the problem you described of the barrel collapsing under NORMAL operation is a design problem, the system is constantly pulling a vacuum and pulling-in the barrel. A PRV wont be helpful in this case, it will end up being permanently open, so reducing the effectiveness of your dust extractor. The solution is as referred too above is to strengthen the barrel or increase the pipe diameter.
However a PRV is a good safety feature. As some have commented the proper place for it is as close to the motor as possible, that way it protects all the upstream pipework and barrel. However it is often convenient to fix it to the top of the barrel - practicle flat surface to mount it, as pointed out by 'Sometime wood worker' once it is triggered it will reduce the effect of the cyclone, but if its only purpose is as safety relief used once in a while that's ok. If you plan to use the value to add in bypass air, then its best fitted downstream as near to the motor as possible, as shown in one of the YouTube clips.
Personally I regard the PRV as primarily a safety feature that will protect the motor and pipework from an abnormal event, when the pipe gets blocked. But that's my preference
I hope that is clear summary of what has gone before - this topic seems to attract a lot of heated agreement which is confusing. Let me know if you need a further explanation. Best wishes Tom
