What are the two square holes for?

[RLWP]

Just now, David Mack said:

453.

And where did you find that?

[David Mack]

In one of my ancient BCN guidebooks.

Wolverhampton Level 473 ft

Birmingham Level 453 ft

Walsall Level 408 ft.

[Guest]

1 hour ago, ditchcrawler said:

Have you seen how ridged the flexible suction hose is and how long it would need to be to go from the pump suction up over the railings and then down to the water without being damaged

But we're they like that when those holes were first created.?

 

I genuinely don't know.

[RLWP]

3 minutes ago, David Mack said:

In one of my ancient BCN guidebooks.

Wolverhampton Level 473 ft

Birmingham Level 453 ft

Walsall Level 408 ft.

Perfect. 453 foot it is

 

Richard

[nb Innisfree]

Real world max suction lift is approx 27'. Suction hose is ridged to allow flexing and also helps prevent it collapsing under atmospheric pressure. 

 

Or is it 26', can't remember, memory fade... 

Edited October 23, 2018 by nb Innisfree

[ditchcrawler]

1 hour ago, MJG said:

But we're they like that when those holes were first created.?

 

I genuinely don't know.

Probably worse, remember these hoses are working at a negative pressure depending on how far down the water is and have to be strong enough not to collapse unlike their discharge hoses.  This is an American video but at 1 minute in you see the suction hoses

 

[nb Innisfree]

2 hours ago, MJG said:

But we're they like that when those holes were first created.?

 

I genuinely don't know.

I went to training school in '74 and hard suction we used was ribbed then, probably WW2 vintage, heavy duty rubber, heavy being the operative word. 

[Jen-in-Wellies]

3 hours ago, RLWP said:

Go on then, extend your pedantry - what range might you get in Birmingham? The New Main Line is around 490 feet above sea level

 

Richard

Using this https://www.mide.com/pages/air-pressure-at-altitude-calculator

To calculate air pressure at the Birmingham 453' and Wolverhampton 473' level, all other things being equal there is a difference of 72.25Pa over the 20'. This works out as 7.37Kgf/m², or 7.37mm of water head difference, assuming 1kg/l water density, so the fire engine can suck up water slightly higher on the Brum level than the Wolverhampton level!

Jen?

Edited October 23, 2018 by Jen-in-Wellies

[RLWP]

23 minutes ago, Jen-in-Wellies said:

Using this https://www.mide.com/pages/air-pressure-at-altitude-calculator

To calculate air pressure at the Birmingham 453' and Wolverhampton 473' level, all other things being equal there is a difference of 72.25Pa over the 20'. This works out as 7.37Kgf/m², or 7.37mm of water head difference, assuming 1kg/l water density, so the fire engine can suck up water slightly higher on the Brum level than the Wolverhampton level!

Jen?

Yebbut...

 

I gave you a figure of 33.8 feet of water, and you rightly pointed out that the figure will vary with water temperature and atmospheric pressure. To make it interesting I threw in the altitude as this would reduce the height that can be pumped

 

What's the variation in lift on the New Main line due to temperature and pressure? I.e. what's the greatest and least?

 

Just for fun, you understand

 

Richard

[bizzard]

1 hour ago, ditchcrawler said:

Probably worse, remember these hoses are working at a negative pressure depending on how far down the water is and have to be strong enough not to collapse unlike their discharge hoses.  This is an American video but at 1 minute in you see the suction hoses

 

That fireman looks full of giant Hotdogs amd Mega Burgers.

[Dr Bob]

1 hour ago, Jen-in-Wellies said:

Using this https://www.mide.com/pages/air-pressure-at-altitude-calculator

To calculate air pressure at the Birmingham 453' and Wolverhampton 473' level, all other things being equal there is a difference of 72.25Pa over the 20'. This works out as 7.37Kgf/m², or 7.37mm of water head difference, assuming 1kg/l water density, so the fire engine can suck up water slightly higher on the Brum level than the Wolverhampton level!

Jen?

What happens if they suck up a fish?

[TheBiscuits]

8 hours ago, Jen-in-Wellies said:

<pedant>Slightly more if the water is warm, or the air pressure is high. Slightly less if it is cold, or the pressure is low!</pedant>

There is no need to be pressures about it.  Sheesh, the atmosphere in here

 

[philjw]

10 hours ago, Dr Bob said:

What happens if they suck up a fish?

Shouldn't happen. The brigade use a coarse filter on the suction pipe. It used to look like a bottle made of wicker work. May be more hi tech now.

Edited October 24, 2018 by philjw
spelling

[Jen-in-Wellies]

11 hours ago, RLWP said:

Yebbut...

 

I gave you a figure of 33.8 feet of water, and you rightly pointed out that the figure will vary with water temperature and atmospheric pressure. To make it interesting I threw in the altitude as this would reduce the height that can be pumped

 

What's the variation in lift on the New Main line due to temperature and pressure? I.e. what's the greatest and least?

 

Just for fun, you understand

 

Richard

Hi Richard,

Using the same calculator. If sea level pressure is 101mb, then at an altitude of 453 feet on the New Main Line, a rise in temperature from 15 to 16C will drop the pressure by 5.66Pa, which reduces the possible water lift by 0.577mm! A 1millibar drop in air pressure is 100Pa, which will reduce the possible water lift by 10.2mm, so more significant than going from the Birmingham to the Wolverhampton level, which reduces lift by 7.37mm. Since the barometer on my wall goes from 950mb (stormy), to 1050mb (sunny), a potential 100mb swing, or around 1metre difference in water head, air pressure is the most significant for lifting water by suction, followed by altitude, with temperature coming third. All this ignores the effect of temperature on water density, which will  very slightly reduce the amount of reduction of suction lift with increasing temperature.

 

The moral of this is if you need the services of the City of Birmingham Fire Brigade during an air raid, make sure that you're near a low canal bridge with a hose access door, on the Birmingham level, with cold, high pressure weather. Unless, of course it is so cold that the canal is frozen! Fortunately the Luftwaffe had a preference to raid on clear nights, rather than stormy, so air pressure is more likely to be high.

 

Jen, who needs to get out more! ?‍?

10 hours ago, Dr Bob said:

What happens if they suck up a fish?

Fried fish! Send round to the chippy for some chips.

Edited October 24, 2018 by Jen-in-Wellies

[RLWP]

Excellent!

 

A metre difference is a lot! it knocks the 33.8 feet down to about 30 foot. On the wider bits of canal, there  must be quite a few bridges who's parapet is about that height from the water. And that's the point when no water is delivered

 

It's sunny out, give it a go

 

Richard

[philjw]

2 minutes ago, RLWP said:

On the wider bits of canal, there  must be quite a few bridges who's parapet is about that height from the water. And that's the point when no water is delivered

I wonder if there are any bridges that are too high for water to be sucked up but still have the gates?  That would result in some frustrated firefighters if they ever tried to get water.

[RLWP]

I was curious about another aspect of this feature of Birmingham canals. I found the answer:

 

https://www.google.co.uk/maps/@52.4837929,-1.9089275,3a,60y,136.77h,80.96t/data=!3m6!1e1!3m4!1sa5fuOKPMNfJ5N_wQe1opzQ!2e0!7i13312!8i6656

 

Richard

[tree monkey]

4 hours ago, Jen-in-Wellies said:

Hi Richard,

Using the same calculator. If sea level pressure is 101mb, then at an altitude of 453 feet on the New Main Line, a rise in temperature from 15 to 16C will drop the pressure by 5.66Pa, which reduces the possible water lift by 0.577mm! A 1millibar drop in air pressure is 100Pa, which will reduce the possible water lift by 10.2mm, so more significant than going from the Birmingham to the Wolverhampton level, which reduces lift by 7.37mm. Since the barometer on my wall goes from 950mb (stormy), to 1050mb (sunny), a potential 100mb swing, or around 1metre difference in water head, air pressure is the most significant for lifting water by suction, followed by altitude, with temperature coming third. All this ignores the effect of temperature on water density, which will  very slightly reduce the amount of reduction of suction lift with increasing temperature.

 

The moral of this is if you need the services of the City of Birmingham Fire Brigade during an air raid, make sure that you're near a low canal bridge with a hose access door, on the Birmingham level, with cold, high pressure weather. Unless, of course it is so cold that the canal is frozen! Fortunately the Luftwaffe had a preference to raid on clear nights, rather than stormy, so air pressure is more likely to be high.

 

Jen, who needs to get out more! ?‍?

Fried fish! Send round to the chippy for some chips.

Absolutely genius,  I have no idea what your talking about but it's genius

[BWM]

Here is a couple of pictures of similar cut outs in the wall of St Bernards hospital, the fact that they are next to the bricked up entrance to the former wharf suggests that they are a later addition. 

[RLWP]

4 minutes ago, tree monkey said:

Absolutely genius,  I have no idea what your talking about but it's genius

Right. Imagine the air is like a big stack of Jenga blocks

[nb Innisfree]

4 hours ago, philjw said:

Shouldn't happen. The brigade use a coarse filter on the suction pipe. It used to look like a bottle made of wicker work. May be more hi tech now.

Metal screw on filter then basket strainer tied on over that. 

[Dr Bob]

1 hour ago, nb Innisfree said:

Metal screw on filter then basket strainer tied on over that. 

 

What if its a little fish?

Edited October 24, 2018 by Dr Bob

[Mike55]

1 hour ago, Dr Bob said:

 

What if its a little fish?

Once it's been through the pump, it'll be fish paste.

[Scholar Gypsy]

Rather amusingly, they have been installed on some modern bridges as well. 

3 hours ago, tree monkey said:

Absolutely genius,  I have no idea what your talking about but it's genius

I don't think the argument works. If the water level is being sucked upwards then the free surface will only move if the water comes from somewhere..

[Tacet]

8 hours ago, RLWP said:

Excellent!

 

A metre difference is a lot! it knocks the 33.8 feet down to about 30 foot. On the wider bits of canal, there  must be quite a few bridges who's parapet is about that height from the water. And that's the point when no water is delivered

 

It's sunny out, give it a go

 

Richard

Jen seems to be saying that 100mb equates to 1m - but that is the range based on 950-1050mb rather than the deviation from 1000mb.  So you should have no worries if there is a  fire where the parapet is no higher than 33.8ft  less 1/2m.   

 

Note the careful choice of imperial, metric, decimal and fractions to make it all so much simpler.  We should really be using pounds force per square metre for pressure.  Not to be confused with pounds feet or foot pounds, of course.