water level glass

A very popular starting point for Live Steam. With their low cost comes a number of problems which can be discussed here
peter holcombe
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water level glass

Post by peter holcombe » Mon Jul 31, 2017 8:56 am

Hi All
Having just bought a second hand MSS side tank loco,As the sight glass was so limescaled up
i thought i would replace with a new one after 5 mins or so the sight glass blew a hole in it
under pressure.
Do i need to put some sort of sealer around the o ring or glass before refitting the brass back head.
Thanks for any help

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Re: water level glass

Post by avalon » Mon Jul 31, 2017 1:09 pm

It sounds like the plastic in your new sight glass is not correct.
Polycarbonate works very well even at high pressures up to 40psi so I guess you have got hold of something like Acrylic or PETG which soften
at lower temperatures and would fail.
Don't forget the the boiling point of water at 40psi is much higher than 100C.
Where did you get the new 'glass' from?

Regards

Vic

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Re: water level glass

Post by peter holcombe » Tue Aug 01, 2017 11:27 am

Hi Vic
it was a new one bought from manor models
i have ordered 2 more new ones but while talking i was
asked if the saftey valve blew which it didnt so perhaps a new one of these
is required.
One on order so we will see,do i put a thin film of gasket sealer to the o ring ?
many thanks for your reply
Peter

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Re: water level glass

Post by avalon » Tue Aug 01, 2017 2:33 pm

I checked the Manor site and it describes the replacement lens as 'Perspex" which is a brand name of Acrylic sheet. Perspex is available as a cast form which softens at up to 110C but this is more expensive than the commonly used extruded form which softens at around 102-105C. The continuous service temperature is a maximum of 80C for both.
I would not recommend Perspex for use in this application.
Please check with Manor in case their description is not correct in which case forget everything above!
Pure water boils at 101C at 15psi, 131C at 40 psi and 145C at 60 psi. so you can see that even at the lowest pressure the lens would be very close to the point at which it would distort and fail.
Polycarbonate is the only readily available plastic sheet for the job.
Assuming you have the standard MSS safety valve, the blow-off pressure is set at about 15psi but this can be increased to around 25psi by substituting a modified valve such as listed by Dreamsteam. Perhaps this is what you have. Of course if the valve jams the pressure will rise and so will the temperature - which is why Manor asked about its condition.

Regarding using a sealer, this should not be necessary and might even add further complications. All you need to do is thoroughly clean the brass recess in the boiler end to remove any residues such as limescale before you fit the new nitrile O ring.

I hope this helps!

Vic

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Re: water level glass

Post by Boustrophedon » Tue Aug 01, 2017 10:47 pm

That stupid piece of plastic spoils the whole Mamod range for me. It's a bad design; Difficult to actually see through, difficult to seal and any plastic used for the window, will be operating close to its softening point, I have tried several.

I will be using pyrex (borosilicate) glass when the next one fails. Apart from the one in my loco, where I am replacing the whole boiler with a Roy Wood sourced silver soldered boiler with a proper sight glass.

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Re: water level glass

Post by avalon » Wed Aug 02, 2017 7:06 am

I haven't given up on plastic yet - it just needs to be the right one!
My last attempt to explain what I thought was going on was not good enough. I hope this is better.

Peter tells us
1 The safety valve does not blow
2 He has a bad seal and queries using gasket sealant
3 The lens has blown a hole in it

What I think is happening is as follows -
As we know water boils at normal atmospheric pressure of about 15psi. If the water is in a sealed boiler fitted with a MSS safety valve set at 15psi, the water would be under a total of 30psi for it to open and would need to reach 121C to boil.
The lens is mounted on a synthetic rubber O ring and the total thikness is about .5mm more than the depth of the recess in the boiler back. The back plate secures the lens in place by squeezing the O ring flat to form a pressure seal.
The spec sheet for Perspex Extruded sheet states that the softening point is around 102 -105C.
As the water in the boiler rises in temperature the plastic softens and at 20psi it reaches 109C which is enough for the O ring to expand into the acrylic and loose the compression seal. If this happens you can see the slight indentation on the edge of the lens when it is removed.
As the seal is broken, water seeps out and this reduces the boiler pressure enough for to it to be unable to reach 15psi and activate the safety valve. However,if the seal could still hold some pressure the temperature would be high enough for the lens to blow.
If the boiler is heated slower it would allow more time for the acrylic to flow and the failure temperature would be even lower.
My experience is that Polycarbonate works well. The softening point is typically around 160-165C and that is enough to withstand the higher temperature even if a 25psi valve is fitted (131C).
One last point. The lens acts as a sort of safety valve and even polycarbonate would blow fairly harmlessly before the boiler exploded.

regards

Vic

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Re: water level glass

Post by peter holcombe » Wed Aug 02, 2017 2:39 pm

WOW
Thanks for all the info Vic, you certainly know your stuff
glad that you answered my question,i have ordered a polycarbnate one as you suggest
when all up and running i will let you know.I still have ordered a new safty valve (better safe than sorry)
Again many thanks for all the infomation Vic it is nice to know that some people out there are always
willing to share good advice.
Many thanks
Peter

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Re: water level glass

Post by CSL » Thu Aug 03, 2017 2:52 pm

So... am I just lucky that I'm having no problems with the original sight "glass" on my ancient SL3 which I've been running since April with a 20-25psi safety valve? Can I expect future issues?

I have actually purchased an MSS replacement as the water level is difficult to see, but I haven't yet fitted it and I'm now wondering whether it might cause problems which don't currently exist (like the MSS wheelsets I've referred to in another thread!).

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Re: water level glass

Post by peter holcombe » Fri Aug 04, 2017 12:01 pm

So... am I just lucky that I'm having no problems with the original sight "glass" on my ancient SL3 which I've been running since April with a 20-25psi safety valve? Can I expect future issues?

Hi CSL
I only changed mine because it was so scaled up i could not see anything.
Peter

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Re: water level glass

Post by Chris Cairns » Fri Aug 04, 2017 1:10 pm

In my experience the problem with sealing these sight glass's is down to two problems.

1. They were originally sealed using an oval shaped seal. At some point in the Mamod ownership takeovers this seal was changed to a thin 'O' ring, and this is what is still supplied now by MSS. My solution here is either use a thicker cross section 'O' ring, or use the oval seal that Mamod use with their current screw fitted sight glass's (you may need to trim the outer edge of these oval seals so it does not get compressed inwards by the boiler punched recess when screwing down the backplate).

2. There are varying depths of the punched out recess at the back of the boiler - a deeper recess will give more problems when combined with the thin 'O' rings as above.

You can see the problem, and my solution here on a kit built MSS - https://youtu.be/KYQ0w6eqIoI?t=4m16s

In the early days of Mamod SLs in Garden Railways, many just removed the sight glass & soldered a brass plate in place. Proper glass sightglass's have been tried as well, although hardly any have been successful (mine cracked on screwing down the backplate). You would probably need to fit seals to both sides of the glass (just like Wilesco do) but keeping the outer seal in place between the brass back plate & the sightglass would be the problem there?

Chris Cairns

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Re: water level glass

Post by peter holcombe » Fri Aug 11, 2017 2:09 pm

Hi All
Well lots to report. Sight glass is fitted and works fine,the plastic one came first so fitted it to try
and works fine.
Replaced the safty valve just to be sure works great.
While on cooldown i noticed a lot of bits in the funnel,turns out to be limescale,i have
stripped the boiler down and i cant belive how much lime scale is in there, soaking in vinigar at the moment.
I will get this loco to steam up and run to its potential, oh the joys of starting in live steam.

Peter

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Re: water level glass

Post by avalon » Sat Aug 12, 2017 7:08 am

Hi Peter

It's good to hear that the site glass problems are over.

When you've got rid of the boiler limescale it might be worth using Halfords' de-ionised battery top up water as it's suitable for lime fee applications including domestic irons!

At £5.50 per 5 litres, it works out at about elevenpence per boiler full!

Vic

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Re: water level glass

Post by Chris Cairns » Sat Aug 12, 2017 12:15 pm

avalon wrote: it works out at about eleven pence per boiler full!
And £35 for a replacement boiler.
Roundhouse Engineering wrote:De-ionized water - this is often sold for use in steam irons and the general opinion amongst the small scale live steam community is that it should not be used. Because of the way it is 'purified', it can cause long term problems by slowly removing zinc from the brass fittings - commonly called de-zincification.
Chris Cairns

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Re: water level glass

Post by avalon » Sat Aug 12, 2017 3:15 pm

So if we can't use that what do you recommend?

Vic

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Re: water level glass

Post by peter holcombe » Sat Aug 12, 2017 4:43 pm

Interesting about the battery water,i always thought that rain water was best ?,
clean of course i filter it before use is this not correct i would be
interested to find out.
one of the best things i have done in a while was join this forum learning
new things every day,even after 40 years of modelling
Cheers guys
Peter

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Re: water level glass

Post by Chris Cairns » Sun Aug 13, 2017 8:06 am

avalon wrote:So if we can't use that what do you recommend?
The right water to use is a controversial subject online.

Roundhouse have a good technical section on their website, which includes their views on water - http://www.roundhouse-eng.com/tech.htm#water

Accucraft say to use filtered rain water or distilled water.

Regner say to use distilled water but to add 5% tap water - they use brass boilers.

Our tap water here in South Lanarkshire is soft (30 PPM) so I just use that. I treat all my locos as if they are fitted with a brass boiler & drain the water out if they are not going to be run again for awhile.

Chris Cairns

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Re: water level glass

Post by Abiogenesis » Tue Aug 22, 2017 7:42 pm

Hello.
This is my first post here. At the end of May this year, I started to watch many videos on YouTube about garden railways & thought of having some kind of a layout myself. After watching Roly Williams fire up his Hornby G100 “Rocket”, I persuaded my eldest son to relinquish his 34 year old G100 (bought when he was born) from its pride of place on his sideboard. I was prompted to resurrect my Mamod ST1 as well, which I had purchased from Hamleys in 1962, as a 20th birthday present to myself.

Some years ago, I replaced the G 100’s original gas tank & at the same time I also lagged the boiler with Rockwool, but didn’t run it & it became only a display item. I placed it on chocks & fired it up three times & discovered that the burner on WOT did not generate enough heat to produce the results I saw in Roly’s video. I disassembled the gas line & fittings & they were all clear. I was left with the burner & so, purchased a preowned spare from Tony Green. Before its arrival, I erroneously concluded that the boiler had a leak, because further dismantling revealed that the glass fibre insulation was wet. Prudence dictated that I should seek professional advice, so I sent the boiler to Western Steam for examination. Geoff tested it hydraulically to 100 psi & it will be back soon, fitted with their 40 psi safety valve.

Meanwhile, I turned to Ebay & successfully bid for an SL1 with only one cylinder. It came with an oval of Mamod track & a Mamod open coal wagon. I was delighted. Having already completed some research, I concluded that Roy Wood Models had the upgrades I desired, so a pair of his upgraded cylinders with “O” ring fitted pistons were ordered, together with steam turret, needle valve regulator, displacement lubricator with drain, water top-up valve, a 40 psi safety valve & a number of decorative embellishments. Here I must praise Roy Wood for his valuable & constant help, whilst I struggled to climb the learning curve of Mamodification.

The plastic sight glass ruptured & led me to reducing the loco to only its running chassis, whilst I figured a way to replace the drilled out rivets on the boiler. Copper wire enabled me to position two bolts, but how to seal them? I salvaged a piece of Rubbaseal roofing from the skip (my youngest son is a bricklayer & is building himself a loft conversion in our roof space) & cut small washers to place on each side of bolt, where it passed through the boiler. This enabled me to secure the brass backhead in place. It worked very well.

About six days ago, loss of steam pressure led me to suspect that the sight glass had failed again. I had to remove gas tank & ceramic burner, the displacement lubricator & reposition the regulator, before I could gain access. I then realised that the sight glass had not leaked, nor had the Rubbaseal washers given way. It was the work of only about fifteen minutes before I had the loco in steam again. It was the steam dome insert that was the culprit. Back when I had the boiler out of the chassis & had substituted the RWM regulator & steam pipe for the Mamod original, I had also cut off & soldered the steam pipe where it exited the bottom of the boiler & had plugged the pipe with solder beneath the steam dome fitting, but I had not noticed that the insert was loose. I used a gas fired torch to effect a permanent repair, then sprayed the SL1 with heat resistant, red brake caliper paint.

I should also mention that a few days ago, a Mamod trainset with a guards van, a log carrier & an open coal wagon appeared on Ebay. Again, I was fortunate. Another gas burner from Forest Classics was fitted to Loco No 2 & I have a set of similar motive power upgrades for it on order from RWM. More rails & two sets of points have also been purchased & attempts to run two trains at once, have resulted in moments of high drama & downright panic.

This morning, I fitted the RWM cylinders to Loco No 1 again, after first deciding to solder the bolts that secure the brass backhead. I also soldered the steam dome fitting to the boiler, because of the constant leaks. It does not take long to reassemble Loco No 1 because I have cut down the cab. The safety valve lifted within 5 minutes & with three wagons heavily loaded with shingle & timber, plus a guard’s van with 1lb of lead sheet on the floor, Loco No 1 raced away with three full turns on the regulator. It got to the curve before I did & derailed disgracefully. I then attached Loco No 2 dead in tow & the added weight made little difference. Is it possible for an SL1 to be too powerful for its own good? After a few 50 feet circuits the loco stopped abruptly & would move in neither direction when pushed. An inspection revealed that the hind pair of wheels had shifted on their axle. Judicious work with pliers rectified the problem & I levered the triangular tabs with a steel punch to tighten the wheels.

Continuing to blow off, the loco hauled its load for more uncounted circuits & I failed to take account of the increased steam consumption. The train halted & it was the smell of burning paint that alerted me; that & the ruptured water sight plastic. AArrrggghh! No useable spares! What to do?

Tesco sell boxes of 100 white interdental sticks (toothpicks), labelled Pro Formula. These boxes are semi-transparent & very tough. I cut out two strips & shaped them & tried them both at the same time under the brass backhead. Too thick. Swapping “O” rings enable me to try one piece of plastic & it did not leak at 40 psi hydraulic pressure. Placing the boiler on the gas stove, the safety valve soon lifted. I viewed the plastic sight glass from afar with binoculars. No leaks. After four minutes, I turned off the gas & let the boiler cool. I have just removed the backhead & inspected the plastic. There is the very slightest impression of the rectangular slot on the surface of the plastic, but it’s considerable less that the imprint on the Mamod items. I could only just see it with my forger’s headset. Those are my findings. Make of them what you will. I’ve no idea what type of plastic was used in China to manufacture these boxes. It’s tough as old boots. I'll send samples to those who would like to repeat the experiment.

Regards,

Perry

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Re: water level glass

Post by Abiogenesis » Wed Aug 23, 2017 10:25 am

Belay that idea about the substitute water sight glass. It failed on this morning's first run. It's not as thick as the Mamod item, which seems to be 2mm thick. There was discussion in this thread about the merits of solid polycarbonate sheet. Google found me a supplier for a single sheet of 2mm x 50mm x 50mm for £0.75, but they want a low order fee of £13-50,bringing the price with VAT to £18. :lol:

It's like reinventing the wheel.

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Re: water level glass

Post by avalon » Wed Aug 23, 2017 5:28 pm

Don't do it!

Go to www.tamstar.co.uk and order a 'sample'
100 x 100mm 2mm A £0.99 delivered.
It works !

Vic

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Re: water level glass

Post by avalon » Wed Aug 23, 2017 5:57 pm

It might be easier to go to
http://www.ebay.co.uk/itm/CLEAR-PLASTIC ... o2vl1b6saw
I hope this connects but I'm not too good at internet stuff!

Regards

Vic

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