# Dewalt dust extractor DVW902M - annoying alarm



## chriscrofty (14 Jun 2017)

Hi folks,

I have a Dewalt DVW902M dust extractor, for cutting up MDF sheets etc and generally it's very good (suction, auto on/off). However, it makes a horrendous alarm sound when the flow drops below a certain level. This could be just from using a tool, like a sander, that doesn't let sufficient airflow through or from a blockage.

Obviously being told about a blockage is useful in some cases, but there is no way of adjusting the settings to accommodate tools with lower airflow. Does anyone else have this DE? Any easy workarounds? 

I have though about using a Y connector to allow additional airflow, but also wondered whether it would be possible to replace the alarm with an LED? This would need some nifty wiring and would voiding the warranty so any other ideas would be appreciated.

In addition to the loud alarm it also makes a constant ringing/buzzing noise in the background. No idea where from or why... again any ideas would be appreciated and I'll look into them.

Chris


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## No skills (15 Jun 2017)

From the model number it sounds like a class m machine, the alarm is there for your safety as annoying as it is  

Sound like you need to add an adjustable air bleed somewhere between the tool and the hose to allow extra air in so the extractor doesn't think it's blocked.

Some m class extractors have ways of self cleaning their filters to keep flow rates up (and you safe  ) whilst you are working - some vibrate the filter others use blasts of air etc, this might be what your hearing.


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## ComfortablyNumb (19 Jun 2017)

Has it not got a dial in front to adjust for different diameters of hose and air flow? 22-27-36-50?


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## sunnybob (20 Jun 2017)

are you sure its a flow loss alarm? the only thing I could find on a quick search is an automatic clean alarm, which can be turned off and reset.
if it is a flow loss alarm, can you find it? usually they are whats known as "sail" switches which have an adjustment on them for fine tuning.


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## chriscrofty (21 Jun 2017)

Thanks for the replies - It's definitely the flow loss alarm and it does have a dial, but even turned to the minimum it's still goes off using some tools because it's not just the hose it's the inlets that can bottleneck the flow. 

Will have a look inside for the sail switches and report back. Thanks


Sent from my iPhone using Tapatalk


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## Amclaussen (10 Aug 2019)

AT LEAST your's is still working! ...
Mine failed in it's electric tool outlet after only two uses (It has to be started manually as the tool outlet does fail to start the dust extractor. The tool outlet is alwas live). I used it with twice with my old Bosch 1587 AVS jigsaw that draws 580 watts at 120 volts 60 Hz (I live in mexico City), so I DIDN'T overload it at all. They did not repair it under warranty because it happened one week after the one year period passed, and I happened to use it only twice in that period! So I asked them about the cost of repair and learned the hard way the they only replace the entire module at more than half the vacuum cost! Disgusted by the abusive DeWalt (lack of) customer support, I preferred to go to a local electronics repair shop, where the clever technician found that the electronic switch (cannot remember right now if it was a Triac or Thyristor) was too small for the task (CHEAP), and was not properly protected against the voltage spikes produced every time an electric motor tool is switched off. BAD design, mediocre performance and WORST support.
Later on I became painful aware that in an excellent comparison of 8 different dust extractors in You-Tube ("Best Dust Extractors Head-2-Head Testing") the lousy DeWalt came last among the eight tested!


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## plywood_king (8 Feb 2021)

Hello,
I had the exact same problem with my DVW902M when using it with an orbital sander. I later added a Y connecter to connect to two orbital sanders. The alarm would not sound as often but still came on every now and again. I have joined the forum with a solution as this is where I came when trying to find one myself.

For those that would like to disconnect the alarm permanently, here's how it's done:

Remove the plate on the front using the appropriate torx bits.
Locate the thin red and black wires that plug into the PCB with a white connector and dissapear into the rear of the vacuum
Disconnect them from the PCB
Your alarm is now disconnected and will not sound. I'm sure this voids your warranty and poses a question over health and safety, though I would argue that the deafening sound of the alarm causes more harm than a slight drop in pressure.

Matt


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## Sachakins (8 Feb 2021)

Use any hoover hose connector, they have a small slider on the handle you slide open to release pressure when your vacuuming something like a rug, to stop it being sucked onto end of cleaner.









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## mr rusty (9 Feb 2021)

You can blame the EU for the annoying alarm.

First, a point - although the standards allow different filter grades in M and H vacuum cleaners, most manufacturers put the _same _HEPA filters in both M and H machines. The big difference is that H versions are also supplied with filter test certificates rather than just a spec sheet. 

The stupid alarm is designed to activate when the filter airspeed drops below 20m/s (it has nothing to do with filter particle size) _when the largest diameter hose the manufacturer sells for that machine is used. - _Think about how stupid that is - if a Manuf sells a 38mm and a 51mm hose for the same machine, they will have different airspeed for the same flow, so the "alarm" calibration is a load of sphericals. It's supposed to show when the filter becomes blinded, but as everyone knows it also goes off every time you restrict airflow at the nozzle. If some machines have adjustments for different hose diameters, it's a manufacturers initiative and not part of the standard.

It gets even more confusing because here in the UK we still have a non-harmonized standard for Type H vacuum cleaners with HEPA filtration suitable for Hazardous dust https://shop.bsigroup.com/ProductDetail?pid=000000000000160257 This standard does not require a flow alarm. Many UK manufactured Type H machines are available commercially, and Type H is still very much a standard recognized by MOD, Nuclear etc. There is no UK-only equivalent of M Class, but in the past many manufacturers supplied (and still do supply) HEPA filtration options for their standard machines - so HEPA filtered vacs have always been available, but now we have to call them "M Class" and put up with the stupid alarm.

M Class and H Class derive from the harmonized EU standard BS EN 60335, which IMHO as far as protection, brings nothing to the party that our own UK BS 5415-2.2:Supplement No. 1:1986 doesn't already cover. It does however introduce the stupid alarm.

The HSE (particularly with regard to asbestos clearing) is totally confused between the difference of Type H and H class, wrapping them together as "the same". Yes the performance is virtually identical, but they derive from different BS which refer to different methods of testing filters.

Moral of the story - go ahead and disconnect your alarm. It won't change the safety, (we all know when a vac is blocked - it stops working), and will save your ears. In fact, according to the standard it doesn't even have to be a sounder - it just needs to be an "indication" - some manufacturers just put a cheap gauge on the machine with a green/red sector.


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## plywood_king (9 Feb 2021)

Thank you mr rusty that is really useful information.


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## Sandyn (9 Feb 2021)

mr rusty said:


> If some machines have adjustments for different hose diameters, it's a manufacturers initiative and not part of the standard.


An alternative way of looking at this problem is that some manufacturers don't think of usability (whoever designed this never actually used it) They don't bother to add the adjustments for alternative hose diameters. They just look for the loopholes in the spec to get their product through at lowest cost. I would change the standard to include 'all supplied accessories' which would force the manufacturers to design a usable product. Far East manufacturers are masters at finding loopholes and even 'cheating'. I think standards can be extremely irritating, but they normally are a very good thing, designed for our protection. Some of them have real inconsistencies, but it can take so long to get the problems flushed though compliance system.


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## mr rusty (9 Feb 2021)

> An alternative way of looking at this problem is that some manufacturers don't think of usability





> Vacuum cleaners of dust class M and class H shall be provided with an indicator which operates before the air velocity, through the largest hose (or tube) supplied by the manufacturer, falls below 20 m/s, referring to the largest section in the hose



Hmm. "useability" - a meaningless air-flow alarm that goes off all the time in normal use. You know it makes sense


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## HDC83 (9 Feb 2021)

plywood_king said:


> Hello,
> I had the exact same problem with my DVW902M when using it with an orbital sander. I later added a Y connecter to connect to two orbital sanders. The alarm would not sound as often but still came on every now and again. I have joined the forum with a solution as this is where I came when trying to find one myself.
> 
> For those that would like to disconnect the alarm permanently, here's how it's done:
> ...



Thanks Matt 
I’m gonna disconnect mine. Just thought it was because I use it with a cyclone hard pipe and blast gates. It can definitely drive you crazy


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## HDC83 (12 Feb 2021)

I opened up the extractor today to disconnect the alarm and found that the clear vacuum pipe was kinked fixed that and has stopped the alarm for now anyway.


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