Windscreen Wipers - Pneumatic v Electric

choochoochoo

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6 Aug 2013
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918
Is there a reason even modern trains (eg 700s) use pneumatics as the main power source for wiper motors ?

I'd have thought electric motors are a better choice for this function.

It can't be the thinking that pneumatics is a better system should there be a power failure? The power required for wiper motors could easily be supplied by a battery for long enough to safely bring a train to a halt in the event of an electrical power loss.

Wipers on modern trains are terrible compared to those on modern cars (which are electric)
 
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Astro_Orbiter

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Electrostars are electric I think, and are pretty consistent, as for aventras, what an absolutely outrageously trash wiper. Fabulous new multi million pound train and they spent 2 quid on a janky wiper. Madness.
 

choochoochoo

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Electrostars are electric I think, and are pretty consistent, as for aventras, what an absolutely outrageously trash wiper. Fabulous new multi million pound train and they spent 2 quid on a janky wiper. Madness.
Exactly same on 700/717s. Terrible wipers. Fast wiper on the train is about as quick as slow wiper is on my car.

They also seem to struggle against the aerodynamic forces at higher speeds.

It's almost like the couldn't be bothered to design it and pinched an old design from a previous model.

And I'm not even going to start on the windscreen washers ineffectiveness.

Not like drivers need to see out the front as best as possible.
 

Pigeon

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Joined
8 Apr 2015
Messages
423
Exactly same on 700/717s. Terrible wipers. Fast wiper on the train is about as quick as slow wiper is on my car.

They also seem to struggle against the aerodynamic forces at higher speeds.

It's almost like the couldn't be bothered to design it and pinched an old design from a previous model.

And I'm not even going to start on the windscreen washers ineffectiveness.

Not like drivers need to see out the front as best as possible.

It always seemed to me that until fairly recently train wipers had only ever been designed about once. Someone came up with these horrible cruddy pneumatic things back when the psssht-thump noises were useful for scaring dinosaurs off the station platforms while the train was waiting, and ever since then whenever a new design of train has needed a wiper someone else has just scrawled "Standard pneumatic motor with No. 3 arm" on the drawings and ticked the box.

It's hard to see why they ever chose it at all unless the design was done so long ago that they still thought making a compact DC motor of a hundred watts or so was too difficult. It's not even an appropriate method for the application because the jerky movement is pretty much guaranteed by the torque on the wiper arm remaining the same regardless of how freely it's moving, so any excessive friction slows it to a crawl and then when it moves off the sticky spot it whacks over at a rate of knots. A series wound electric motor will automatically put out more torque if a sticky bit slows it down and less torque as it speeds up, so to a large extent it self-regulates to a roughly constant speed.

I took one of those pneumatic motors apart once. Full of ancient grease that had turned into glue and the internal friction was outrageous. Don't suppose that sort of thing is much help.

The useless washers certainly don't help. Do they even consistently put any detergent in them at all, and do they ever use something that actually works, or just that counterproductive blue muck they sell in petrol stations? Sometimes I've noticed a few bubbles on something that's been using its washers, but not always and only in comparatively recent times. (Tales of drivers calling ahead to the next station to have a mop and bucket ready...) And trains seem to have an unexpectedly severe problem with collecting a layer of sticky gunk all over the outside; the stuff they have to put in carriage washers to get the visible dirt off the paint needs to be a bit special, and I'm not sure how good it is for the rather specific and different requirements for cleaning glass and not leaving it smeary, or even if it leaves some residue which makes the problem worse.

I wonder if these days where there is an attempt at design the designers are handicapped by a tendency to base their ideas on what the system is supposed to do on what the system in their cars does. I always take care that mine is capable of washing its windscreen crystal clear, and I am more often than not horrified when someone switches their own wipers on to see them create a horrible smeary mess that makes things as much worse as better - and even more so when they don't understand why I'm saying "what a horrible smeary mess, how can you see through that?" If they don't see a problem with using so unnecessarily dysfunctional a system, maybe they don't see a problem with designing one...
 

Aictos

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Exactly same on 700/717s. Terrible wipers. Fast wiper on the train is about as quick as slow wiper is on my car.

They also seem to struggle against the aerodynamic forces at higher speeds.

It's almost like the couldn't be bothered to design it and pinched an old design from a previous model.

And I'm not even going to start on the windscreen washers ineffectiveness.

Not like drivers need to see out the front as best as possible.
Got to ask but what's the problem with the windscreen washers?
 

TRAX

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Aaah, railway windscreen wipers… probably the cheapest and shoddiest mechanical part on every train since the 19th century ! :D
 

ComUtoR

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Is there a reason even modern trains (eg 700s) use pneumatics as the main power source for wiper motors
Are you sure ?

Does the 700 wiper button look like (pic provided) as for the life of me I can't remember.
 

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seagull

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28 Feb 2011
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Class 390 wipers are the work of the devil himself. At anything over 70-80mph in any rain above a light drizzle and you might as well pull the sun blind down or wear a blindfold, visibility is about nil. At slower speeds they sort of work but leave a nice long and wide streaky section right in front of the eye line, so visibility slightly more than nil.
They also occasionally have a habit of gradually working their way across the windscreen from the "stabled" position at high speeds, and as they are big chunky things, that again has the effect of severely reducing visibility once they reach the "across" position which is directly in the eye line.

But, it's not as if you need to see much at 125mph, after all...
 

choochoochoo

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918
Got to ask but what's the problem with the windscreen washers?
They don't spray on to the windscreen. More like they dribble on to the wiper blade and that then smears across the windscreen. I'm sure they use the the water from the cleaner's mop bucket to fill the washer reservoir too !!

Are you sure ?

Does the 700 wiper button look like (pic provided) as for the life of me I can't remember.

I'm sure. The distinct pssst-thunk noise is definitely pneumatic. That's why it's got an isolation cock.

The electric is the 'back-up'. And is just as bad as it's only one speed.
 

TRAX

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Are you sure ?

Does the 700 wiper button look like (pic provided) as for the life of me I can't remember.
Yes it is a pneumatic wiper on the Desiro City, although I don’t get what the switch has to do with it ?
 

ComUtoR

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I'm sure. The distinct pssst-thunk noise is definitely pneumatic. That's why it's got an isolation cock.

The electric is the 'back-up'. And is just as bad as it's only one speed.

Yes it is a pneumatic wiper on the Desiro City, although I don’t get what the switch has to do with it ?
The picture is from a 707.

The normal side is electric and the backup is pneumatic.

I don't have my 700 manual to hand.
 

DelW

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1,935
Just as an aside, car manufacturers have tried pneumatic wipers as well.

In the 1950s Ford fitted wipers "powered" by the vacuum in the inlet manifold. Unfortunately, the vacuum varies with throttle opening, meaning that the wipers slowed or even stopped under maximum acceleration, but sped up when decelerating.

I would hope that any surviving cars from that era have been converted to electric operation by now!
 

Rescars

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It always seemed to me that until fairly recently train wipers had only ever been designed about once. Someone came up with these horrible cruddy pneumatic things back when the psssht-thump noises were useful for scaring dinosaurs off the station platforms while the train was waiting, and ever since then whenever a new design of train has needed a wiper someone else has just scrawled "Standard pneumatic motor with No. 3 arm" on the drawings and ticked the box.

It's hard to see why they ever chose it at all unless the design was done so long ago that they still thought making a compact DC motor of a hundred watts or so was too difficult. It's not even an appropriate method for the application because the jerky movement is pretty much guaranteed by the torque on the wiper arm remaining the same regardless of how freely it's moving, so any excessive friction slows it to a crawl and then when it moves off the sticky spot it whacks over at a rate of knots. A series wound electric motor will automatically put out more torque if a sticky bit slows it down and less torque as it speeds up, so to a large extent it self-regulates to a roughly constant speed.

I took one of those pneumatic motors apart once. Full of ancient grease that had turned into glue and the internal friction was outrageous. Don't suppose that sort of thing is much help.

The useless washers certainly don't help. Do they even consistently put any detergent in them at all, and do they ever use something that actually works, or just that counterproductive blue muck they sell in petrol stations? Sometimes I've noticed a few bubbles on something that's been using its washers, but not always and only in comparatively recent times. (Tales of drivers calling ahead to the next station to have a mop and bucket ready...) And trains seem to have an unexpectedly severe problem with collecting a layer of sticky gunk all over the outside; the stuff they have to put in carriage washers to get the visible dirt off the paint needs to be a bit special, and I'm not sure how good it is for the rather specific and different requirements for cleaning glass and not leaving it smeary, or even if it leaves some residue which makes the problem worse.

I wonder if these days where there is an attempt at design the designers are handicapped by a tendency to base their ideas on what the system is supposed to do on what the system in their cars does. I always take care that mine is capable of washing its windscreen crystal clear, and I am more often than not horrified when someone switches their own wipers on to see them create a horrible smeary mess that makes things as much worse as better - and even more so when they don't understand why I'm saying "what a horrible smeary mess, how can you see through that?" If they don't see a problem with using so unnecessarily dysfunctional a system, maybe they don't see a problem with designing one...
Quite agree with your cimments about the blue muck. There used to be a most effective additive called Clearalex. Anyone know what was in it? It was great for removing smears from car windscreens. I wonder how it would have impacted rail grime equally well.
 
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sw1ller

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4 Jan 2013
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1,466
Exactly same on 700/717s. Terrible wipers. Fast wiper on the train is about as quick as slow wiper is on my car.

They also seem to struggle against the aerodynamic forces at higher speeds.

It's almost like the couldn't be bothered to design it and pinched an old design from a previous model.

And I'm not even going to start on the windscreen washers ineffectiveness.

Not like drivers need to see out the front as best as possible.
That made me laugh, the water jet on our 175s seem to be pointed anywhere but where you want it to go! Drives me bonkers.
 

driverd

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In fairness, its one of the excelling points on the new CAF stuff - they actually work, and can keep the screen clean... that is until the blades start to deteriorate.

Pneumatic wipers are a total nightmare, more distracting than staring through the rain, when they do actually work in a half decent, none hypnotic fashion, there's usually enough water leaking through the inside of the window that you may as well have not bothered.

The other problem is speed. Heaven forbid someone design wipers that remain fully in contact with the windscreen above circa 50 mph...
 
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172007

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Class 172x have electric wipers. They work well, get the occasional smearing when the blades get old but they get changed if you put it into the book.

The water jet is odd. /2&3's it's electric whereas the 0/1's it's by air. The electric ones are really good if the pipe or nozzle is Aimed correctly at the screen; again pop into maintenance book and they are generally done quickly and are fine. The air powered screen swash is generally rubbish with more foam than actually liquid.

The 2/3's do both windscreens. The 0/1's gave a selector as to both or drivers screen. Nearly all units only ever have the drivers screen cleaned or wipers operating in rain. Guess many 172 drivers are only used to looking out of the drivers window due to the gangway in the way in most of the fleet.
 

robbeech

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11 Nov 2015
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3,608
I do like this forum. A group of drivers discuss that these 400tonne bits of metal carrying 500 people at up to 125mph are driving blind when it rains and we all chuckle and get on with our day. :)

Just as an aside, car manufacturers have tried pneumatic wipers as well.

In the 1950s Ford fitted wipers "powered" by the vacuum in the inlet manifold. Unfortunately, the vacuum varies with throttle opening, meaning that the wipers slowed or even stopped under maximum acceleration, but sped up when decelerating.

I would hope that any surviving cars from that era have been converted to electric operation by now!
OT, and washer not wipers but i think it was 1984 before Ford stopped using the air pressure in the spare wheel to pump water to the rear washers on some of their smaller cars.
 

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