From Overs Pianos <sec@overspianos.com.au>
Hi Terry,
>I recently purchased a 5 hp cyclone dust collector/separator for my
>woodworking shop. It has yet to be delivered. I would like to
>solicit input from any of you folks that have used/installed one of
>these units - or maybe even someone who has just put some thought
>into it.
Haven't installed one yet, but have done some research on the
subject. We're making plans to install a complete workshop system
after I return from Rochester, cashed up after receiving the final
payment for piano no. 6.
> My air-conditioned concrete-block shop is attached to the rear of
>my concrete-block 2-car garage. I have been thinking of installing
>the cyclone in the garage, piping through the shop and exhausting
>outside the rear of the shop with no filters. This has the advantage
>of keeping a lot of the noise out of my shop and no hassles with
>filters. The downside of such an installation is that the garage is
>very close to my neighbor's nice back porch with pool (the noise
>might be a problem) and all the air that is exhausted outside the
>shop has to be made up with outside air coming back into the shop
>(half the year, humid and hot) - if this thing actually moves
>anything close to 1,500 CFM, it will replace all the air in my shop
>every six minutes or so.
Yes, this approach will avoid the use of filters, but you'll be
losing the workshop air that you've either heated or cooled,
depending on the season. A 5 hp unit with appropriately sized ducting
should pull around 2300 CFM. The manufacturer should be able to
supply you with a flow chart for the unit, which plots CFM flow
against restriction of the ducting in inches water gauge. When you
design the system, don't forget to include the restriction of the
flexible hose which connects the fixed duct to your machine. The
flexible ducts are very lossy (these also vary considerably between
makes - try to source one with a smooth inner bore).
I've uploaded the performance chart of a 5 hp unit that we're
considering, to my personal webspace at;
http://members.optusnet.com.au/ronovers/25SDC.jpg
You can see on the chart the flow of this unit, with no restriction,
is its fully rated 3200 CFM. At 10 inches water gauge the flow is cut
to 2000 CFM and at 16 inches WG the flow falls to zero. The chart
performance for each pump will depend on the design of the housing
and in particular the impeller design. A straight bladed impeller
will give you a higher unrestricted flow but will fall dramatically
when subject to restriction. A backward curved impeller will give you
less CFM at no restriction, but will deliver more CFM at a high
restriction (which is the way it will operate most of the time). The
best units use impellers with backward curved blades. Backward curved
impellers also deliver a higher efficiency so they tend not to heat
the air so much as it passes through the cyclone and back into the
workspace.
You should be able to design your system so that the restriction of
the system is low enough to enable the unit to pull the required
number of CFM to keep the system clear and the workplace clean.
The general rule of thumb is that you size the runners to your
machines so that the air velocity is around 4000 ft/min, with the
horizontal main duct sized so that the air velocity is around 3500
ft/min. In your case the calculations will be simple since you'll
have only one machine operating at any time. The vertical runners,
which usually run up from the machine to the main runner, require are
higher velocity to lift the chips to the main runner, but once they
arrive at the main runner 3500 ft/min is adequate to keep the duct
clean. The use of a smaller main duct will cause unnecessary
restriction which will lower the overall performance of the system.
If the restriction is too severe it may restrict the air velocity to
such a degree that wood chips become permanently lodged in the
ductwork. If you get a copy of Woodshop Dust Control, this writer
will take you through the entire process of designing a system which
works. He also publishes the water gauge losses of pipe section sizes
at the air velocities of 3500 and 4000 ft/min. You can calculate the
losses at different velocities from the table yourself, since air
restriction goes up according to the square of the increase in air
velocity. In other words, if you increase the air velocity by a
factor of 2, the restriction in the system will be four times
greater. The design of a system is quite straightforward with the
help of a good publication such as the one previously mentioned.
I've just about decided that I will make the ductwork from
polyethylene (PE) pipe, since it is available in a great range of
diameters. It is very important, when designing a system, that the
runner diameters are appropriately sized. Runners which are too large
will have insufficient air velocity to keep the wood chips in the air
flow, while runners which are too small will cause too much
restriction for the cyclone to pull the required CFMs and keep the
machines clean. We'll be installing spiral earth wires around the
runners to prevent static build up and the risk of an explosion.
Another advantage of PE pipe is that large radius sweep bends are
available, which will allow for the construction of relatively
low-loss branch junctions.
> The alternatives are to install it inside the shop and exhaust
>through filters inside the shop (noisy, filter expense and hassle).
The idea of mounting the unit in your garage is a good one, since it
will keep the noise of the unit away from your work space. It will
also keep the noise contained in your garage which will please your
neighbours (unless there are no doors on the garage). If your garage
has no doors you may eventually need to enclose the unit to keep
noise down.
If you are running the outlet back through your shop then exhausting
it outside, why don't you consider setting up some column style
filters along one of your workshop inside walls? These filter types
require a distribution plenum at the top (preferably just underneath
ceiling level), to which is attached a number of tubes of filter
material. The filter tube lengths are set so that they just reach low
enough to be connected to collection buckets on the workshop floor.
The filters are attached to the collection buckets with large hose
clamps. The cyclone will remove most of the dust down to around 5
micron (1/5 th of one thou). The filter media will take care of the
particles down to 1 micron. The advantage of this system is that you
get to keep the air in the shop at a suitable temperature. There will
be some heating which comes from the inefficiency of the impeller,
which will have a slight workshop-warming effect in the winter and
place a little more load on your air conditioner during the summer.
But overall, the air con' will cope a lot easier than it would if you
simply plumb the exhausted air from the cyclone out to the
atmosphere. Your neighbour's pool will probably stay a bit cleaner as
well.
Looking forward to meeting some of you listers at Rochester.
Isn't living fun some of the time.
Ron O.
--
OVERS PIANOS - SYDNEY
Grand Piano Manufacturers
_______________________
Web http://overspianos.com.au
mailto:ron@overspianos.com.au
_______________________