Advantage of larger diameter on vacuum cleaner hose?

[gremlin_95]

Hi all,

My Numatic George vacuum cleaner comes as standard with a 32mm hose for
dry use which is 1.9m in length, I was on the look out for a new hose
and gave Numatic a call asking what different lengths can be obtained.
The chap told me it is possible to also use a 38mm hose on the vacuum,
however when asked what the advantage would be, he couldn't really answer.

Is there any advantage at all of having a 38mm hose, apart from the
obvious that larger objects wont block the hose as easily as they would
with a 32mm hose...

--
David

[mogga]

On Fri, 20 Jan 2012 16:56:21 +0000, gremlin_95 <daw**dseed@g**ail.com>
wrote:

Pick up the stuff that is big enough to block the hose!

You'll just get bigger furballs evolving up there!
--
http://www.voucherfreebies.co.uk

[Moonraker]

My logic, which is often faulty, tells me that the vacuum at the hose
end would be lower, so would not suck up as well.

--
Residing on low ground in North Staffordshire

[RJS]

Ha Ha! Exactly my recent experience.

I'm finding that my new Nilfisk was supplied by a very narrow,
concertina, hose which blocked at every opportunity. It now has a
full-bore tube and has yet to block. Also, the motor sounds much less
frantic with the bigger tube.

Richard

[gremlin_95]

Did it make much difference to the suction?

--
David

[The Medway Handyman]

Your logic isn't far wrong.

A bigger hose will mean lower 'suction' (not vacuum) but higher airflow.

Its a trade off. The suction alone isn't any good without enough
airflow to move the debris along the hose. It depends on what you are
picking up.

Small relatively heavy objects are best picked up by machines with high
suction, lighter bigger objects you are better off with higher airflow.

With twin motor vacuums, where the motors are in parallel the suction
remains the same, but the airflow doubles.

Commercial carpet cleaning machines often use twin vac motors to remove
water from carpets, but they are used in series. The suction increases
by about 25% and the airflow by about 50%.

--
Dave - The Medway Handyman www.medwayhandyman.co.uk

[harry]

> David- Hide quoted text -
>
> - Show quoted text -

A bigger hose reduces resistance and hence increases air flow. This
puts more load on the motor and it runs slower but probably not enough
to matter.

However, if there is no air flow (hose blocked off), the vacuum will
be exactly the same as before. (And the motor will run at it's maximum
speed consuming least electricity).

[gremlin_95]

Thanks for that explanation. It's mostly used for vacuuming cars. Think
I will stick with the current 32mm hose. The larger Numatic vacuum with
twin motors seem to have 38mm hoses and 80l/sec airflow as opposed to
George with 40l/sec.

--
David

[gri...@gmail.com]

On Fri, 20 Jan 2012 11:00:05 -0800 (PST), harry <harol...@aol.com>
wrote:

>However, if there is no air flow (hose blocked off), the vacuum will
>be exactly the same as before. (And the motor will run at it's maximum
>speed consuming least electricity).

And then overheat.

[harry]

On Jan 21, 12:12 am, grim...@gmail.com wrote:
> On Fri, 20 Jan 2012 11:00:05 -0800 (PST), harry <haroldhr...@aol.com>

> wrote:
>
> >However, if there is no air flow (hose blocked off), the vacuum will
> >be exactly the same as before. (And the motor will run at it's maximum
> >speed consuming least electricity).
>
> And then overheat.

Depends on how the motor ventilation is arranged but it would take a
while.

[The Medway Handyman]

Direct cooled motors use the air they are sucking to cool the windings,
by-pass motors have separate cooling fans.

[RJS]

On Jan 20, 6:13 pm, gremlin_95 <daw**dseed@g**ail.com> wrote:

No, in fact I think that the suction actually improved because the
motor was not struggling to pull the air through a narrow hose.

My, very old, AquaVac has a hose which is the same size as the
prelacement hose for the Nilfisk and it will pick up 1/4 bricks!

It's interesting to note that the narrow hose issued with the Nilfisk
has an adaptor to make if fit the big-bore hole on the collection
tank. I've asked Nilfisk why the supply the narrow hose.

Richard

[RJS]

On Jan 20, 7:00 pm, harry <haroldhr...@aol.com> wrote:

>
> A bigger hose reduces resistance and hence increases air flow. This
> puts more load on the motor and it runs slower but probably not enough
> to matter.
>

So, am I missinterpreting the quieter motor noise caused by the larger
hose allowing greater air flow when I concluded that the motor sounded
as though it was under a lower load? Sorry if that's really
convoluted!

Richard

[Gazz]

> Is there any advantage at all of having a 38mm hose, apart from the
> obvious that larger objects wont block the hose as easily as they would
> with a 32mm hose...

Depends on the diameter of yer cock, some people find the standard 32mm hose
chafes a fair bit during a vacuum assisted milking session.... so i've been
told.


I'm remembering the subject on here last year about the hoover nozzle that
sliced the power cord in half, and all the suggestions that went with it,
few days later i was in john lewis, and picked up the dysoon handheld vac on
display, battery was full, so turned it on and blocked the end with my palm,
the motor then started pulsing on and off,
my GF burst out laughing, and said 'typical, i can buy a vibro for under a
tenner, yet the male equivalent is over a hundered quid!'

[harry]

If you think about it, the fan absorbs power by accelarating air from
zero to some speed.

If you cut off the air flow, the motor is just churning round the
same air and doing no work except for motor losses and air friction
losses inside the fan housing.
A commutator motor will speed up and use less current.
An induction motor will speed uponly slightly and use less current.

I seem to remember the power/speed relationship with fans is a cube
law.
ie it takes eight times the power to drive a fan twice as fast.

And a square law speed to pressure
ie four times the power double the pressure/suction.

So it makes a big difference.

If you block the blow side of the air flow the fan will thrash round
in high pressure air.
If you block the suck side,it will thrash around in near vaccuum.

So in the latter case, it will use the least power.

From the current readings, things about the fan performance/efficiency
can be deduced.
I forget the details, it was years ago we done these things at tech.

[The Medway Handyman]

On 22/01/2012 09:21, harry wrote:
> On Jan 21, 12:04 pm, RJS<alt...@excite.com> wrote:
>> On Jan 20, 7:00 pm, harry<haroldhr...@aol.com> wrote:
>>
>>
>>
>>> A bigger hose reduces resistance and hence increases air flow. This
>>> puts more load on the motor and it runs slower but probably not enough
>>> to matter.
>>
>> So, am I missinterpreting the quieter motor noise caused by the larger
>> hose allowing greater air flow when I concluded that the motor sounded
>> as though it was under a lower load? Sorry if that's really
>> convoluted!
>>
>> Richard
>
>
> If you think about it, the fan absorbs power by accelarating air from
> zero to some speed.
>
> If you cut off the air flow, the motor is just churning round the
> same air and doing no work except for motor losses and air friction
> losses inside the fan housing.
> A commutator motor will speed up and use less current.
>

This is true. If you put an amp meter on a vacuum cleaner & block the
suction the amps drop. BTDTGTTS.