On Sun, 17 Jul 2011 19:11:47 +0100, Andy Champ wrote:

On 16/07/2011 13:09, Andy Breen wrote:

Use of vacuum as an important part of the working cycle wasn't banished
by Trevithick either: his most effective and longest-lasting engine
type, the Cornish mine engine, used high-pressure steam on one side of
the piston and vacuum on the other - made it a very efficient power
source for its day.


It's lasted a bit longer than that.

You know those big cooling towers on power stations? The turbine
exhaust is into a partial vacuum...


More assistive than providing 50% or so of the power output, though.

I did think of mentioning the use of condensers to assist the efficiency
and output of stationary and marine HP machinery, including turbines,
but decided not to as there seemed to be enough confusion about
the workings of simple pistons machinery...

--
From the Model M of Andy Breen, speaking only for himself

On Fri, 15 Jul 2011 12:12:23 -0700, Andy Dingley wrote:

On Jul 15, 2:12Â*pm, Andy Breen wrote:

Except there were. Only in the early days, I'd admit, but the first
commercially successful locomotives (and the first locomotives to be
built as more than prototypes, and the first exported..) had cast-iron
boilers.

Which ones? Most of Trevithick's had cast iron shells (still with a
wrought iron endplate), but I can't think of any others, or of any
"first exports" (which one?)

The Murray/Blenkinsop machines, one of which was exported to Germany (and
another one built there). Both the German examples had cast boilers,
as did at least the first pair of machines at Middleton. At least one
of the later Middleton machines had a wrought iron boiler. I'm not
sure if there is any evidence one way or another for the ones used
at Coxlodge, and the Nant-y-Glo machine is distinctly obscure.

that were cast iron. Certainly the Tyneside
builders were using wrought iron from the outset - although they still
managed to have boiler explosions, including Locomotion itself.

Pearce contends that Locomotion underwent a flue tube collapse - much less
dramatic - and the boiler barrel explosion was another locomotive of
the initial 5 built.

There is some possibility that Brunton's Mechanical Traveller (the one
with the walking legs) was built with a cast boiler, but it had been
fitted with a wrought iron boiler just before it was destroyed by a
boiler explosion.

The Brunton machine used at Crich certainly seems to have had a cast boiler.
The second(?) one may well have done so before being reboilered.

--
From the Model M of Andy Breen, speaking only for himself

OK: I'm now writing with Sheila Bye's paper on the Murray/Blenkinsop machines,
John Crompton's paper on the Hedley machines, Mike Clarke's paper on the
first locomotives on the European mainland and Andy Guy's paper on
NE locomotive pioneers 1805-27 open in front of me (first
two in Early Railways 2, second two in Early Railways 1)..

On Sun, 17 Jul 2011 18:54:39 +0000, Andy Breen wrote:

On Fri, 15 Jul 2011 12:12:23 -0700, Andy Dingley wrote:

On Jul 15, 2:12Â*pm, Andy Breen wrote:

Except there were. Only in the early days, I'd admit, but the first
commercially successful locomotives (and the first locomotives to be
built as more than prototypes, and the first exported..) had cast-iron
boilers.

Which ones? Most of Trevithick's had cast iron shells (still with a
wrought iron endplate), but I can't think of any others, or of any
"first exports" (which one?)

The Murray/Blenkinsop machines, one of which was exported to Germany
(and another one built there). Both the German examples had cast
boilers, as did at least the first pair of machines at Middleton. At
least one of the later Middleton machines had a wrought iron boiler. I'm
not sure if there is any evidence one way or another for the ones used
at Coxlodge, and the Nant-y-Glo machine is distinctly obscure.

The Bye paper makes it quite clear that the first three machines at Middleton
(at least) had cast boilers. The fourth one differed in a number of ways
and /may/ have had a wrought-iron boiler, but this cannot be confirmed
from surviving information. The machines built for the Orrell Colliery at
Wigan did have wrought boilers. Nothing known either way about the Nant-y-Glo
machine, and the later Kenton and Coxlodge machines, at least, differed in
dimensions from the Leeds engines (and perhaps also in construction?) - Bye,
ER2; Guy, ER1 (Coxlodge only).

The Blenkinsop machine built in Berlin for the ironworks at Chorzow had a
cast boiler - made in two halves and bolted together (details in Dusseldorf
archive).
The second - also Berlin-built - machine of the same type, for Saarland, also
had a cast boiler (Clarke, ER1). No details are given for the Blenkinsop
machine built for Leige.

that were cast iron. Certainly the Tyneside builders were using wrought
iron from the outset - although they still managed to have boiler
explosions, including Locomotion itself.

Not from the beginning. The Winfield/Steele 'Gateshead' engine of 1805 had
a cast boiler, as did Hedley's first machine of 1812-13 ('Black Billy',
built on the manually-operated test chassis).
To quote Hedley:
"An engine was then constructed, the boiler was of cast iron"
(William Hedley, letter to the Newcastle press on 10 December 1836, cited
in Crompton, ER2).
The later 2-cylinder engines had wrought iron boilers.

Chapman seems to have used wrought iron boilers from the outset. That
would include the Whitehaven machine of 1812, though the putative
Swainson 'Trevithick' of 1808 may have used a cast boiler - if it
existed!

Pearce contends that Locomotion underwent a flue tube collapse - much
less dramatic - and the boiler barrel explosion was another locomotive
of the initial 5 built.

There is some possibility that Brunton's Mechanical Traveller (the one
with the walking legs) was built with a cast boiler, but it had been
fitted with a wrought iron boiler just before it was destroyed by a
boiler explosion.

The Brunton machine used at Crich certainly seems to have had a cast
boiler. The second(?) one may well have done so before being reboilered.

I made a mistake here. The Crich machine is described by Guy (ER1) as
having a wrought iron boiler. Given that Brunton made a great point
of the novel construction of this boiler (claimed to be safe to 400-500 psi)
it is reasonable to assume that the Newbottle machine, in both original
and modified form, used a wrought iron boiler too.

Stephenson was pretty good at covering the traces of his first two(?) -
unsatisfactory and probably derivative - geared-drive engines, but in
view of the parallels between these machines and Chapman's work
wrought iron is likely. 1814 seems late for a cast iron boiler in a
British-built locomotive anyway.

--
From the Model M of Andy Breen, speaking only for himself

On Jul 17, 4:45*pm, harry wrote:

I used to fly. *

Dear god...

On Sun, 17 Jul 2011 17:03:54 +0000 (UTC), Andy Breen
wrote:

On Sun, 17 Jul 2011 17:49:27 +0100, Charles Ellson wrote:

On Sun, 17 Jul 2011 16:25:57 +0000 (UTC), Andy Breen
wrote:

On Sun, 17 Jul 2011 17:15:30 +0100, Charles Ellson wrote:

On Sun, 17 Jul 2011 08:48:47 -0700 (PDT), harry
wrote:

On Jul 17, 4:23*pm, Charles Ellson wrote:
On Sat, 16 Jul 2011 23:28:13 -0700 (PDT), harry
wrote:

On Jul 16, 9:27*pm, Andy Dingley wrote:
On Jul 16, 7:07*pm, harry wrote:

The staem was used to flush air out of the cylinders.

Er no, the air was displaced by the steam being fed into the
cylinder. Get your intentions and consequences in the right order.

So where exactly is the diffence?

"Flushing" is generally the deliberate rather than consequential
purging of a substance from somewhere. If you are referring to the
animation at the top of the above Wonkypaedia article then no such
process is shown but if any does take place then it will (except at
startup) be "expired" steam that is flushed rather than air.

Opening a valve to admit steam to the cylinder seems deliberate enough
to me.

It's fairly clear from his own writings that Mr Savery was of the same
opinion:

"Then skrew in the faid pipes again as tight as possible. Then lightthe
fire at B No.1. When the water in L boyles, the handle of the regulator
mark'd Z, must be thrust from you as far as it will go, which makes all
the steam rifting from the water in L, pass with irriftible force
through O No.1 into P No.1 pushing out all the air before it, through
the clack R No.1 making a noise as it goes."

'The Miner's Friend, or, An Engine To Raise Water By Fire', Thomas
Savery, S. Crouch, 1702, available on-line at:

http://library.thinkquest.org/C00601...am%2Fsavery%2F

To me, that implies a very deliberate use of the steam to flush out the
air in the working vessel..

That device looks distinctly different to the one in the Wikipaedia
article.

What? Counting on Wikipedia as an authority here?

Nope, referring to what someone else mentioned earlier. I don't think
we've been considering the same piece of technology.

Rather than using a piston it seems to use alternative positive
and negative pressure (relative to atmosphere) in a vessel with valves
arranged so that water is sucked in from below then discharged up to the

Yes. Newcomen's engine was essentially a combination of ideas from
Papin (piston-in-cylinder) and Savery (use of condensation of steam
to create a vacuum to raise water). The working principles, in
terms of the use of steam to expel the air from the working vessel
and then condensation to provide the working force, however, were
the same as Newcomen's machine - a fact recognised by Newcomen
himself, as he conceded that his machine was covered by Savery's
patent (the small number of Newcomen engines installed before
the expiry of Savery's patent was a result of this - the patent
royalties made them even more expensive).

surface. As often occurs, older descriptions can be somewhat simplistic;
the purpose is clearly to propel water while any propulsion of air is
consequential to some being present but not necessary for the ongoing
process.

The text clearly shows that Savery understood that his engine worked
by replacing the air in the working vessel with steam which could then
be condensed to create a vacuum, with the latter being used to raise
water (exactly the same principle as was adopted to a cylinder/piston
and separate boiler by Newcomen).

Maintaining otherwise shows a disregard for primary evidence which
surprises me in your case (I'd expect it from Michael, or Bruce
in recent years, but not you).

On Jul 17, 5:07*pm, Andy Breen wrote:
On Sat, 16 Jul 2011 20:04:31 +0000, Andy Breen wrote:
On Sat, 16 Jul 2011 20:49:23 +0100, Clive wrote:

In message , Andy Breen
writes
The pet-cock,
Any similarity between this and the modern clack valve?

As I understand it, the pet-cock was for bleeding steam off from the
pump: "by opening (the pet-cock) the steam in the pump was let out, and
the action renewed" (Marshall, again).

I'd not expect a direct similiarity to anything on a "modern" steam
engine, as even the ones that use hot feed and pumps have the pump well
away from the boiler (and seals are much better, anyway)

Thinking some more...

The clack valve is - essentially - a non-return valve to stop boiler steam
getting back into the feed system, nyet? Presumably the pumps used in early
locomotives had non-return valves in them (well, they must have, being
intended to push water one way...), but it's clear from Marshall's comments
("hot water entered from the leaking of the valves, causing them (the pumps)
to be filled with steam") that they didn't work well enough to keep the
pumps at their duty. Given the materials available at the time, it's
easy to see how this happened - and given that until then most applications
requiring continuous working[1] had been the domain of low-pressure engines,
with Trevithick-type[2] high-pressure engines restricted to more intermittent
tasks[3] where the boiler could be topped up after each burst of work
(pressure having dropped then, anyway..), it's easy to see how the problem
hadn't been encountered before. The valves had worked well enough for low-
pressure (and stationary!) boilers, after all (actually, the battering
taken by the machinery in an unsprung locomotive on short - 3'-4' rails -
can't have helped the functioning of the pump valves at all!).

Essentially, if they could have made a really good clack valve, they'd
not have had the problem with the pumps locking and the pet-cock wouldn't
have been needed. As materials available meant they couldn't, the pet-cock
was a real breakthrough in producing a locomotive which could run more than
a very short distance between extended (and madly hazardous!) stops.

--
From the Model M of Andy Breen, speaking only for himself

There is a problem with all boiler feed water pumps and that is
cavitation.
When the feedwater gets hot enough (dependent on the feedwater tank
elevation), the pump ceases to function due to cavitation. If this
happens for long enough, the pump is irrepairably damaged.
Reciprocating pumps are especially prone to this.

On Jul 17, 7:11*pm, Andy Champ wrote:
On 16/07/2011 13:09, Andy Breen wrote:



Use of vacuum as an important part of the working cycle wasn't banished by
Trevithick either: his most effective and longest-lasting engine type, the
Cornish mine engine, used high-pressure steam on one side of the piston and
vacuum on the other - made it a very efficient power source for its
day.

It's lasted a bit longer than that.

You know those big cooling towers on power stations? *The turbine
exhaust is into a partial vacuum...

Andy

All steam prime movers these days are fitted with some means of
condensing the exhaust steam. It gains them another 15psi/1bar of
pressure.
Also it enables the condensate to be recovered for re-use.

One reason for steam locomotives being so inefficient is that there is
no practical means of doing this.

On Jul 17, 9:38*pm, Andy Dingley wrote:
On Jul 17, 4:45*pm, harry wrote:

I used to fly. *

Dear god...

Beyond your capabilities I suppose....
I entered competitions too . Won occasionally.

On 18/07/2011 08:12, harry wrote:
On Jul 17, 7:11 pm, Andy wrote:
On 16/07/2011 13:09, Andy Breen wrote:



Use of vacuum as an important part of the working cycle wasn't banished by
Trevithick either: his most effective and longest-lasting engine type, the
Cornish mine engine, used high-pressure steam on one side of the piston and
vacuum on the other - made it a very efficient power source for its
day.

It's lasted a bit longer than that.

You know those big cooling towers on power stations? The turbine
exhaust is into a partial vacuum...

Andy

All steam prime movers these days are fitted with some means of
condensing the exhaust steam. It gains them another 15psi/1bar of
pressure.

It also gains them another 80 degrees or so of temperature difference
between the heat source and heat sink, which significantly increases the
maximum possible efficiency of the heat engine, according to the second
law of thermodynamics.
--
Jeremy Double {real address, include nospam}
Rail and transport photos at
http://www.flickr.com/photos/jmdoubl...7603834894248/

On Jul 18, 8:16 am, harry wrote:
On Jul 17, 9:38 pm, Andy Dingley wrote:

On Jul 17, 4:45 pm, harry wrote:

I used to fly.

Dear god...

Beyond your capabilities I suppose....
I entered competitions too . Won occasionally.

were those the ones where you launch yourself off a seaside pier?

Jim K

Andy Champ wrote:

You know those big cooling towers on power stations? The turbine
exhaust is into a partial vacuum...

Indeed so. Some low pressure turbine casings include a special
explosion vent comprising a thin metal sheet normally sucked onto
a mesh frame, with a sharp spike poised above it. If pressure
becomes positive, the metal bulges and is pierced by the spike to
vent to atmosphere. I remember working on the control relays
which, as vacuum fell, opened the turbine hall roof vents, so
that the anticipated blast didn't take all the windows out.

Chris
--
Chris J Dixon Nottingham UK


Have dancing shoes, will ceilidh.

On Jul 17, 8:11*pm, Andy Champ wrote:
On 16/07/2011 12:34, Clive wrote:

Very low pressures are entirely feasible considering that the steam was
only used to raise a piston which through a beam allowed what it was
working on (Man engine etc.) To drop, the steam was the condensed by
spraying in cold water and the atmospheric pressure on the other side of
the piston did the work.

Lower than you think. *The beam was usually raised just by the weight of
the pump on the other end; *the purpose of the steam was just to push
the air out. *Then the condensation led to a partial vacuum, and the air
pressure does all the real work.

You guys really must go to Crofton Beam Engines. *When they are in
steam, of course!

http://www.croftonbeamengines.org

The Kew museum also has some large beam engines that are steamed from
time to time. My recollection is that they were built as Watt engines
(negligible boiler pressure) but converted to work on the "Cornish
Cycle" (using Trevithick's strong steam) later-ish in life.

Robin

On Jul 16, 1:12*pm, The Natural Philosopher
wrote:

The need for pressure arises out of the need for efficiency so that a
locomotive can do reasonable distances carrying its own coal and water,
particularly water.

It is no accident that the high pressure "strong steam" engine was
developed in Cornwall. Oop north, the mines produced coal, so fuel
was plentiful and cheap, and making a more efficient pumping engine
was a low priority. In the Cornish tin mines, any fuel for the
engines had to be imported from eg south Wales, so fuel cost was much
more important to the economics of the mining operation. Hence, this
drove the move to more efficient engines, which allowed engines to
become compact enough to become mobile.

Robin

On Jul 18, 8:50*am, Jim K wrote:
On Jul 18, 8:16 am, harry wrote:

On Jul 17, 9:38 pm, Andy Dingley wrote:

On Jul 17, 4:45 pm, harry wrote:

I used to fly.

Dear god...

Beyond your capabilities I suppose....
I entered competitions too . Won occasionally.

were those the ones where you launch yourself off a seaside pier?

Jim K

No. Is this your experience?

On Jul 18, 12:09*pm, bob wrote:

It is no accident that the high pressure "strong steam" engine was
developed in Cornwall. *

They weren't. Trevithick was from Cornwall, but he had to go to Wales
to find backers for his strong steam work. Cornwall needed single-
acting stationary engines for pumping, so they found the best way to
efficiency (not being constrained by size) was by working at the low
end of the cycle (compounding and condensing) and developing things
like the Woolf and Bull engines.

The last Cornish engine was built in the 20th century, in North Wales
(Dorothea quarry). They certainly weren't made obsolete overnight by
Watt or Trevithick

On Jul 18, 8:07*am, harry wrote:

There is a problem with all boiler feed water pumps and that is
cavitation.

Utter ********. Cavitation is a problem of _low_ pressure in pumps,
sufficient to form bubbles (i.e. "cavities"). The one thing we know
about a boiler feedwater pump of any form is that it has to work at
around boiler pressure. Whilst the Giffard injector stops working with
hot water, heat isn't a big problem for pumps.

In message
,
Andy Dingley writes
Whilst the Giffard injector stops working with
hot water, heat isn't a big problem for pumps.
Indeed, the colder the water the better the feed and ease of operation.
--
Clive

On Tue, 19 Jul 2011 02:21:32 -0700, Andy Dingley wrote:

On Jul 18, 8:07Â*am, harry wrote:

There is a problem with all boiler feed water pumps and that is
cavitation.

Utter ********. Cavitation is a problem of _low_ pressure in pumps,
sufficient to form bubbles (i.e. "cavities"). The one thing we know
about a boiler feedwater pump of any form is that it has to work at
around boiler pressure. Whilst the Giffard injector stops working with
hot water, heat isn't a big problem for pumps.

Um.. Cavitation occurs when water boils against a surface, and the collapsing
bubbles can lead to pitting and damage to that surface. The cause is localised
boiling as a result of low pressures in those regions.
In marine propellors, of course, it occurs at ambient temperatures and
very low pressures, but there's no reason at all why it couldn't occur
in a pump if the feed temperature were hot enough and the small drop
in pressure produced at some point in the pump were large enough for
the water to begin to boil.

--
From the Model M of Andy Breen, speaking only for himself

On 19/07/2011 11:49, Andy Breen wrote:
On Tue, 19 Jul 2011 02:21:32 -0700, Andy Dingley wrote:

On Jul 18, 8:07 am, wrote:

There is a problem with all boiler feed water pumps and that is
cavitation.

Utter ********. Cavitation is a problem of _low_ pressure in pumps,
sufficient to form bubbles (i.e. "cavities"). The one thing we know
about a boiler feedwater pump of any form is that it has to work at
around boiler pressure. Whilst the Giffard injector stops working with
hot water, heat isn't a big problem for pumps.

Um.. Cavitation occurs when water boils against a surface, and the collapsing
bubbles can lead to pitting and damage to that surface. The cause is localised
boiling as a result of low pressures in those regions.
In marine propellors, of course, it occurs at ambient temperatures and
very low pressures, but there's no reason at all why it couldn't occur
in a pump if the feed temperature were hot enough and the small drop
in pressure produced at some point in the pump were large enough for
the water to begin to boil.

Cavitation occurs at any place within a pump where the liquid pressure
falls below the vapour pressure of the liquid being pumped. This could
be at a surface, but doesn't have to be.

It typically occurs where the fluid enters the pump, where it has been
accelerated, but before energy has been imparted to the liquid by the
pump mechanism. According to Bernoulli's law, as the liquid is
accelerated, its pressure falls.

It's a particular problem where the liquid is close to its boiling
point. As the problem occurs at the entry to the pump, the pressure
that the pump is delivering to is irrelevant, so it can occur with a
boiler feed pump working with condensate.

If you were pumping condensate that was not sub-cooled (i.e. still at
its boiling point and condensation pressure at the pump inlet), then
cavitation is very likely.

If you ever look at an oil refinery or petrochemical plant, you will
notice that the distillation columns do not sit on the floor, but are
raised several metres above ground level on "skirts". This is so there
is a hydrostatic head above the bottom product pumps, so that cavitation
doesn't occur.

--
Jeremy Double {real address, include nospam}
Rail and transport photos at
http://www.flickr.com/photos/jmdoubl...7603834894248/

On Tue, 19 Jul 2011 13:10:16 +0100, Jeremy Double wrote:

On 19/07/2011 11:49, Andy Breen wrote:
On Tue, 19 Jul 2011 02:21:32 -0700, Andy Dingley wrote:

On Jul 18, 8:07 am, wrote:

There is a problem with all boiler feed water pumps and that is
cavitation.

Utter ********. Cavitation is a problem of _low_ pressure in pumps,
sufficient to form bubbles (i.e. "cavities"). The one thing we know
about a boiler feedwater pump of any form is that it has to work at
around boiler pressure. Whilst the Giffard injector stops working with
hot water, heat isn't a big problem for pumps.

Um.. Cavitation occurs when water boils against a surface, and the
collapsing bubbles can lead to pitting and damage to that surface. The
cause is localised boiling as a result of low pressures in those
regions. In marine propellors, of course, it occurs at ambient
temperatures and very low pressures, but there's no reason at all why
it couldn't occur in a pump if the feed temperature were hot enough and
the small drop in pressure produced at some point in the pump were
large enough for the water to begin to boil.

Cavitation occurs at any place within a pump where the liquid pressure
falls below the vapour pressure of the liquid being pumped. This could
be at a surface, but doesn't have to be.

True - though the problems arise when it comes close to a surface (generally
speaking - in submarine propulsors non-contact cavitation noise was an issue
at one stage, I believe..).

But yes, it doesn't need to be on a surface. My bad.

/chomp/

It's a particular problem where the liquid is close to its boiling
point. As the problem occurs at the entry to the pump, the pressure
that the pump is delivering to is irrelevant, so it can occur with a
boiler feed pump working with condensate.

Yep..

If you were pumping condensate that was not sub-cooled (i.e. still at
its boiling point and condensation pressure at the pump inlet), then
cavitation is very likely.

Agree.

If you ever look at an oil refinery or petrochemical plant, you will
notice that the distillation columns do not sit on the floor, but are
raised several metres above ground level on "skirts". This is so there
is a hydrostatic head above the bottom product pumps, so that cavitation
doesn't occur.

So.. it does happen in pumps (sorry, Andy D.), and it might have occured
in locomotive boiler pumps under some circumstances (e.g. early locomotives
just after the tender tank had been refilled with boiling water from the
lineside kettle, hot-feed under some circumstances e.g. early locomotives
on the underground lines...).

--
From the Model M of Andy Breen, speaking only for himself

On Jul 15, 11:54*am, Andy Breen wrote:
Boiler explosion or firebox collapse? Actual (external) explosion of the
boiler barrel seems to have been (commendanbly rare for over a century
- the benefits of elfandsafety gorn madde, of course..).

Last boiler barrel explosion on a British railway was at Buxton in
1921 I believe. Considering how many steam locomotives were in
service they do seem to have been fortunately rare.

Firebox collapse is will be damned unpleasant for those on the engine,
but much less deletrious for the surrounding neighbourhood.

Indeed.

On Jul 19, 10:21*am, Andy Dingley wrote:
On Jul 18, 8:07*am, harry wrote:

There is a problem with all boiler feed water pumps and that is
cavitation.

Utter ********. Cavitation is a problem of _low_ pressure in pumps,
sufficient to form bubbles (i.e. "cavities"). *The one thing we know
about a boiler feedwater pump of any form is that it has to work at
around boiler pressure. Whilst the Giffard injector stops working with
hot water, heat isn't a big problem for pumps.

Well old son I ran steam boilers for thirty years with many sorts of
boiler feed pumps. I have seen all manner of mishaps and failure.
The cavitation takes place on the suction side of the pump as even a
half wit such as yourself would realise with a momentst hought.
Cavitation is the commonest reason for boiler feed pump failure.
The pressure it works at depends on the control system for boiler
water level but often rises very considerably above boiler pressure.
You only theory men need to keep quiet.

On Jul 19, 10:39*am, Clive wrote:
In message
,
Andy Dingley writes Whilst the Giffard injector stops working with
hot water, heat isn't a big problem for pumps.

Indeed, the colder the water the better the feed and ease of operation.
--
Clive

The feedwater temperature is between a rock and a hard place. Cooler
is better for the pumps.
But hotter is better for boiler efficiency and dearation of the makeup
water.
The boiler feedwater tank needs to be as high as possible to minimise
possible pump cavitation.

On Tue, 19 Jul 2011 11:26:42 -0700, harry wrote:

On Jul 19, 10:21Â*am, Andy Dingley wrote:
On Jul 18, 8:07Â*am, harry wrote:

There is a problem with all boiler feed water pumps and that is
cavitation.

Utter ********. Cavitation is a problem of _low_ pressure in pumps,
sufficient to form bubbles (i.e. "cavities"). Â*The one thing we know
about a boiler feedwater pump of any form is that it has to work at
around boiler pressure. Whilst the Giffard injector stops working with
hot water, heat isn't a big problem for pumps.

Well old son I ran steam boilers for thirty years with many sorts of
boiler feed pumps. I have seen all manner of mishaps and failure.
The cavitation takes place on the suction side of the pump as even a
half wit such as yourself would realise with a momentst hought.
Cavitation is the commonest reason for boiler feed pump failure. The
pressure it works at depends on the control system for boiler water
level but often rises very considerably above boiler pressure. You only
theory men need to keep quiet.

Ahem.. the theory of cavitation is that localised boiling can occur
anywhere that pressure is reduced enough to allow the fluid to boil.
It's all about the conditions under which the fluid undergoes a phase
change, after all..
(any other interpretation is a result of mis-understanding the theory)
I've not worked with boiler feed pumps, nor in propellor design or
use, but a simple consideration of thermal physics (plus, I'll admit,
some seminars loooooong ago with Dai Trevena, who was one of the
great experts on understanding cavitation...) tells me that if you
drop pressure enough locally then the fluid is likely to boil, with
bad consequences for any surface it comes in contact with. That's
obvious from the theory..

;-)

--
From the Model M of Andy Breen, speaking only for himself

On Tue, 19 Jul 2011 11:30:10 -0700, harry wrote:

On Jul 19, 10:39Â*am, Clive wrote:
In message
,
Andy Dingley writes Whilst the Giffard
injector stops working with
hot water, heat isn't a big problem for pumps.

Indeed, the colder the water the better the feed and ease of operation.
--
Clive

The feedwater temperature is between a rock and a hard place. Cooler is
better for the pumps.
But hotter is better for boiler efficiency and dearation of the makeup
water.
The boiler feedwater tank needs to be as high as possible to minimise
possible pump cavitation.

To come back to where the discussion of pumps began - in early locomotives
with primitive boilers and small heating surface, the choice between pumping
near-boiler or cold water into the boiler was likely to make the difference
between the machine being able to do useful work and not - hence the near
-universal use of lineside "kettles" to heat water for the locomotives.

--
From the Model M of Andy Breen, speaking only for himself

In message
,
harry writes
The feedwater temperature is between a rock and a hard place. Cooler
is better for the pumps.
But hotter is better for boiler efficiency and dearation of the makeup
water.
The boiler feedwater tank needs to be as high as possible to minimise
possible pump cavitation.
I'm following the mention of the Gifford injector which has no moving
parts and no cavitation.
--
Clive

On Tue, 19 Jul 2011 19:52:45 +0100, Clive wrote:

In message
,
harry writes
The feedwater temperature is between a rock and a hard place. Cooler is
better for the pumps.
But hotter is better for boiler efficiency and dearation of the makeup
water.
The boiler feedwater tank needs to be as high as possible to minimise
possible pump cavitation.
I'm following the mention of the Gifford injector which has no moving
parts and no cavitation.

"Giffard", I think you'll find, named for Henri Giffard...

--
From the Model M of Andy Breen, speaking only for himself

On 19/07/2011 19:52, Clive wrote:
In message
,
harry writes
The feedwater temperature is between a rock and a hard place. Cooler
is better for the pumps.
But hotter is better for boiler efficiency and dearation of the makeup
water.
The boiler feedwater tank needs to be as high as possible to minimise
possible pump cavitation.
I'm following the mention of the Gifford injector which has no moving
parts and no cavitation.

.... but which requires cold water, since the latent heat of the steam
provides most of the pumping power, so the steam has to condense in the
injector for it to work.

--
Jeremy Double {real address, include nospam}
Rail and transport photos at
http://www.flickr.com/photos/jmdoubl...7603834894248/

On Tue, 19 Jul 2011 20:14:18 +0100, Jeremy Double wrote:

On 19/07/2011 19:52, Clive wrote:
In message
,
harry writes
The feedwater temperature is between a rock and a hard place. Cooler
is better for the pumps.
But hotter is better for boiler efficiency and dearation of the makeup
water.
The boiler feedwater tank needs to be as high as possible to minimise
possible pump cavitation.
I'm following the mention of the Gifford injector which has no moving
parts and no cavitation.

... but which requires cold water, since the latent heat of the steam
provides most of the pumping power, so the steam has to condense in the
injector for it to work.

There's a thought.. could the restriction of the Giffard injector to
delivering cold water only be the reason that so many locomotives
were built through the 1860s and 1870s with a single injector and
a feed pump on the other side, with arrangements to heat the tender
water via a steam cock? Because with the small boilers of the day
(imposed by civil engineering limits) using cold feed only would
have had too much of an impact on performance?
The Stirling brothers, certainly, both used single injector plus feed
pumps on a lot of their locomotives - was this part of how the Stirlings
got away with the combination of small, slender boiler (admittedly
with a much better arrangement of tubes than most designers of the
time) and relatively large cylinders?
Later on, of course, the feed pumps were stripped off, leaving but
the single injector. That must have made life difficult.

--
From the Model M of Andy Breen, speaking only for himself

On Jul 19, 7:52*pm, Clive wrote:
In message
,
harry writesThe feedwater temperature is between a rock and a hard place. *Cooler
is better for the pumps.
But hotter is better for boiler efficiency and dearation of the makeup
water.
The boiler feedwater tank needs to be as high as possible to minimise
possible pump cavitation.

I'm following the mention of the Gifford injector which has no moving
parts and no cavitation.
--
Clive
Giffard that would be.
Injectors are never part of land/marine based boilers as they are
extremely prone to cavitation with hot water, esp when steam is
neccesarily mixed with water in the injector. Just because there are
no moving parts, doesn't mean there is no cavitation.
Locomotives almost invariably have cold feedwater.

The object with non-locomotive boilers is to get/keep the feedwater as
hot as possible.
This minimises the need for boiler water treatment and maximises
efficiency.

Boiler feedwater pumps are often multistage to help reduce cavitation
on the impellors.

"harry" wrote in message
...
On Jul 19, 10:39 am, Clive wrote:
In message
,
Andy Dingley writes Whilst the Giffard injector
stops working with
hot water, heat isn't a big problem for pumps.

Indeed, the colder the water the better the feed and ease of operation.
--
Clive

The feedwater temperature is between a rock and a hard place. Cooler
is better for the pumps.
But hotter is better for boiler efficiency and dearation of the makeup
water.
The boiler feedwater tank needs to be as high as possible to minimise
possible pump cavitation.

Cavitation can't have been much of a problem or they would have used a two
stage pump to increase the head in the problem area.

On Jul 19, 7:35*pm, Andy Breen wrote:

Ahem.. the theory of cavitation is that localised boiling can occur
anywhere that pressure is reduced enough to allow the fluid to boil.
It's all about the conditions under which the fluid undergoes a phase
change, after all..

So where in a boiler feedwater pump is such boiling going to occur?
Where is there a drop in pressure (required) where either (one of
which is also required) such a pressure drop approaches below
atmospheric pressures, or else the temperature is approaching the
steam temperature of the boiler? Even with feedwater heating, pump
temperatures are nowhere near this high.

In many cases of cavitation, it's a highly localised situation, where
a high speed pump can dynamically produce a localised low pressure.
This isn't the case for boiler feedwater pumps.

On Jul 19, 7:26*pm, harry wrote:

Well old son I *ran steam boilers for thirty years with many sorts of
boiler feed pumps.

What was it Harry? Was it the drugs that finally did for you?

After your thirty years as the Flying Boilerman, in between your
fellowship at Harvard, you must have been one smart cookie. So what
happened? Because you're a right feckin eejit these days.

On Jul 19, 11:45*pm, Andy Dingley wrote:
On Jul 19, 7:26*pm, harry wrote:

Well old son I *ran steam boilers for thirty years with many sorts of
boiler feed pumps.

What was it Harry? Was it the drugs that finally did for you?

After your thirty years as the Flying Boilerman, in between your
fellowship at Harvard, you must have been one smart cookie. So what
happened? Because you're a right feckin eejit these days.

Compared with you, anyone would appear smart.

On Jul 19, 11:43*pm, Andy Dingley wrote:
On Jul 19, 7:35*pm, Andy Breen wrote:

Ahem.. the theory of cavitation is that localised boiling can occur
anywhere that pressure is reduced enough to allow the fluid to boil.
It's all about the conditions under which the fluid undergoes a phase
change, after all..

So where in a boiler feedwater pump is such boiling going to occur?
Where is there a drop in pressure (required) where either (one of
which is also required) such a pressure drop approaches below
atmospheric pressures, or else the temperature is approaching the
steam temperature of the boiler? Even with feedwater heating, pump
temperatures are nowhere near this high.

In many cases of cavitation, it's a highly localised situation, where
a high speed pump can dynamically produce a localised low pressure.
This isn't the case for boiler feedwater pumps.

Feedwater temperature depends mostly on the percentage of condensate
recovered, the remainder has to be made up with "raw" water, but over
90% is common. Feedwater is often at 80 or 90 dC. So only a moderate
pressure drop will cause this to boil.

Feedwater heating is therfor unneccessary and undesireable in most
locations.
Raw water (to replace lost condensate) is sometimes heated to de-
aerate it.
Thisis done by steam injection usually.
However this only done if condensate recovery is low.

Because (guess what) it can lead to feedwater pump cavitation.

Clearly you have never seen a boiler feedwater pump. They are usually
centifugal high speed pumps,unless it is a monotube boiler in which
case they have to be a positve displacement pump

On Jul 19, 8:33*pm, "dennis@home"
wrote:
"harry" wrote in message

...





On Jul 19, 10:39 am, Clive wrote:
In message
,
Andy Dingley writes Whilst the Giffard injector
stops working with
hot water, heat isn't a big problem for pumps.

Indeed, the colder the water the better the feed and ease of operation..
--
Clive

The feedwater temperature is between a rock and a hard place. *Cooler
is better for the pumps.
But hotter is better for boiler efficiency and dearation of the makeup
water.
The boiler feedwater tank needs to be as high as possible to minimise
possible pump cavitation.

Cavitation can't have been much of a problem or they would have used a two
stage pump to increase the head in the problem area.- Hide quoted text -

- Show quoted text -

Cavitation is a very variable thing. Sometimes it's not aurally
noticeable. sometimes it makes a pump sound likea bag of nails.
Sometimes it's so bad, the pump won't function.
But when you dismantle a feedpump visible damage is virtually always
there.

It's pointless rabbiting on about abstract theory, I'm telling you
what happens in practice.

On 19/07/2011 23:43, Andy Dingley wrote:
Where is there a drop in pressure (required) where either (one of
which is also required) such a pressure drop approaches below
atmospheric pressures, or else the temperature is approaching the
steam temperature of the boiler?

There is a drop in pressure where the liquid accelerates on entering the
pump. According to Bernoulli's law, when a fluid speeds up its pressure
drops.

--
Jeremy Double {real address, include nospam}
Rail and transport photos at
http://www.flickr.com/photos/jmdoubl...7603834894248/

On Jul 20, 12:33*pm, Jeremy Double wrote:
On 19/07/2011 23:43, Andy Dingley wrote:

Where is there a drop in pressure (required) where either (one of
which is also required) such a pressure drop approaches below
atmospheric pressures, or else the temperature is approaching the
steam temperature of the boiler?

There is a drop in pressure where the liquid accelerates on entering the
pump. *

Of course there is. If we're talking about a centrifugal pump, then it
might even get to the stage of cavitation.

I am however unaware of any of Trevithick's engines, or even of any
steam locomotive, using such a pump.

On Wed, 20 Jul 2011 14:55:08 -0700, Andy Dingley wrote:

On Jul 20, 12:33Â*pm, Jeremy Double wrote:
On 19/07/2011 23:43, Andy Dingley wrote:

Where is there a drop in pressure (required) where either (one of
which is also required) such a pressure drop approaches below
atmospheric pressures, or else the temperature is approaching the
steam temperature of the boiler?

There is a drop in pressure where the liquid accelerates on entering
the pump.

Of course there is. If we're talking about a centrifugal pump, then it
might even get to the stage of cavitation.

I am however unaware of any of Trevithick's engines, or even of any
steam locomotive, using such a pump.

The problem with pumps on early locomotives seems to have been boiler
water seeping back past the valves to fill the pump with steam (in
the lower pressure regime there). This appears (from contemporary accounts
of how locomotives were operated) to have prevented boiler feed pumps
from being used effectively, so that locomotive boiler capacity had to
be based not on steam raising power but on water capacity for the intended
length of run - the locomotive had to be stopped for a significant period
for the boiler to be refilled (e.g. the suggestion from Matthew Murray
that for Kenton & Coxlodge a locomotive with a single cylinder and a
larger boiler might be more suitable than the Middleton type, as the run was
longer and more water needed[1]).
Initial methods of re-filling involved blowing down the boiler and refilling,
very quickly a number of engineers (Murray, Chapman..) adopted raised
cisterns which allowed the boiler to be filled while remaining pressurised.
I have to confess that the idea of coupling a cistern of boiling water to
a pressurised boiler - with 1810s valves and couplings - does not leave
me with a warm fuzzy comfortable feeling!
By 1814-15 the 'pet-cock', allowing steam to be bled from the pump,
was in use - this has been repeatedly credited to George Stephenson,
and if true probably represents his great contribution to the development
of a practical steam engine - one that could top up its boiler on the move!
Boiling water feed continued in use to tender tanks/barrels for many
years, of course - even in the 1840s gauge trials there was controversy
caused by some of the SG locomotives starting their runs with pre-heated
water in the tenders, though by this time it was a matter of getting
a bit more efficiency, rather than making the difference between the engine
working and not.
(summarised from Guy, ER4, 'The elusive railway kettle')

[1] In the end they went for close copies of the Middleton engines.

--
From the Model M of Andy Breen, speaking only for himself

On Fri, 15 Jul 2011 15:17:08 +0100, John Williamson wrote:

As far as I know, locomotives all had wrought iron boiler barrels from
the earliest days, with stationary engines using cast iron for parts of
theirs. Then again, early stationary engines normally ran at a maximum
of about 3 or 4 psi.

This set me off thinking and doing some reading up, and that's prompted
a couple of ideas..

Pre-1815 locomotives seem to divide pretty evenly between those with
cast iron and wrought iron boilers (with quite a few undetermined..).

* denotes locomotives built by well-established foundaries or engine-builders
with foundaries, # engines built by local workshops (e.g. colliery workshops)

Cast:
1802-03 Richardson Coalbrookdale machine (completion doubtful)*
1804 Trevithick Pen-y-Darren machine*
1805 Trevithick/Steele/Whinfield Gateshead machine*
1808 Trevithick Catch-Me-Who-Can*
1812-14 Blenkinsop/Murray machines at Middleton (first 3, certainly)*
1813 Hedley 'Black Billy' at Wylam# (boiler*)
1814-15 Blenkinsop/Murray machines in Prussia*

Wrought:
1813 Brunton engine at Crich*
1814 Blenkinsop/Murray machines at Wigan (built by Daglish, Haigh Foundary)*?
1814-16 Chapman Whitehaven locomotive#
1814 Chapman Wallsend locomotive#
1814-16 Hedley 2-cyl locomotives at Wylam#
1815 Stephenson locomotives (chain-coupled)#
1814-15 Brunton locomotive at Newbottle #?

Plus a lot of 'uncatagorised', though the only one of those built by
a major foundary seems to be the 1813 Chapman chain engine for Heaton,
built by Butterley.

With the exception of the Brunton engine at Crich and the Wigan Blenkinsops
(by Butterley and Haigh Foundary respectively), the wrought iron boilers
seem to mainly be the products of local workshops. The only country-built
machine that used a cast boiler was the first Wylam engine ('Black Billy')
- and that boiler was bought in (along with much of the machinery).

Hypothesis: in the early days of locomotive building cast iron was the
preferred material for boilers, but only a limited number of companies
could manufacture such large and complex items. As larger wrought iron
plates became available it became easier for colliery workshops and smaller
local foundaries to build boilers from wrought iron, avoiding buying in
large and expensive items from outside.
The emergence of George Stephenson as the dominant figure in railway practice
from 1816 established the use of wrought iron boilers (as in the Stephenson
standard locomotive) as the norm.

The hypothesis seems to fit available evidence, and oddly I've not seen it
suggested before. Have I missed anything obvious (e.g. actual costings..).
Thoughts/comments welcome..


--
From the Model M of Andy Breen, speaking only for himself