This little note has come from the Kent & E. Sussex heritage railway - a breif account of how and why water is treated. A bit more complicated than at first sight.
"This Is just some Information and theoretical number crunching on as to why we have a water treatment plant on the railway and how It probably does more than you think and how It changes the dynamics on what happens Inside the boiler. Some of you may find this boring and some of you I could be teaching how to suck eggs, but It’s ‘marginally’ Interesting.....Depending on how you see It.
Before the water treatment plant was Installed, the railway filled the locos with raw water, with the water board changing the supply once a month or so depending on the time of year. These change overs still happen now and can cause chaos with predictions.
The current Incoming, untreated water at Rolvenden Is:
Total Dissolved Solids: 310 - 330ppm of which 160ppm Is Hardness, so In reality, the effective TDS Is 150 - 170ppm. Those figures are the same throughout the railway, with Tenterden being slightly higher In hardness.
On an average, our locos will evaporate one boiler full of water per trip and when the water Is evaporated, It leaves the TDS behind. So for every trip a loco does, 170ppm would be left In the boiler, multiplied by how many trips It would do, which Is normally three. This would leave 510 - 600ppm extra of TDS In the boiler per day ontop of what’s already In there. Your healthy limit Is somewhere between 1500 – 1800ppm and at 2000ppm, you will more than likely experience priming of some form. We use blowdown to control the level of TDS In the boiler and nominally, for every Inch of blowdown you do, you will lose 100ppm of TDS.
Example, If the boiler Is already at 1800ppm and It’s going to gain 600 throughout the day (Three trips) you’d blowdown 6” to make room for that gain.
HOWEVER, this does not take Into account the 160ppm of hardness you still have remaining. This will not come out of solution In the blowdown process and the railway was suffering from severe scale build up because of this. A running cycle for us Is 28 days, so over that 28 day period with three trips per day, you’d end up with somewhere between 13 – 20kg of scale formation within the boiler, which may or may not come out during a washout (13 – 20kg of scale Is easily two wheel barrows full, If not more).
If the hardness Is not dealt with and It reaches 350ppm, It will become supersaturated and It’ll start to form very hard scale. This will progressively get worse as It creeps beyond 350ppm. For example, a railway that will remain nameless, was accumulating nearly 70kg of scale In a boiler over the course of 28 days. This unfortunately went unchecked and started forming extremely hard scale and after being back In service for only two years, the crown and side sheets were removed from the boiler as It was completely scaled up and rippled the Inner firebox due to poor heat exchange.
In 1954, a loco on the London Tilbury & Southend Line had 4 tons of scale removed from It over the course of a year. This unfortunately didn't always come out during a washout and the boiler was frequently 'dismantled'.
So anyway, we Installed water softeners! Hurray! No more hard water and scale to worry about! But all of a sudden, the engines started priming to an absolute stand still and the TDS was through the roof! We learnt (the hard way) If you soften water, you’re removing the hardness, which means now, the entirety of the original 330ppm Is now problematic TDS and Is no longer removed from the equation. By fixing the problem of scale formation, we’d doubled the TDS gain per day and after two days of running, you’d already be at 2000ppm In the boiler. After three days, you’d need to do a water change. No degree of blowdown Is going to fix that level of TDS gain and If you let the TDS climb to 8000 – 10,000ppm, even If there Isn’t hardness present and the boiler was somehow only hours old, straight off the shelf (so to speak) It would start corroding. If you reach 15,000 – 20,000 you’d certainly be playing a risky game. The boiler of a locomotive In South America failed after only 8 months from new because of consistently running at 12,000ppm of TDS which corroded the metals. This boiler also had very little scale.
Another railway, which will also remain nameless, suffer from ‘Light Water’ which Is when the entire boiler content turns to foam due to bad water chemistry and very high TDS. Bubbles and foam will be visible In the gauge glass at this point. Because foam has almost no thermal properties, the temperature around the firebox and the tubes will suddenly start to Increase and If the hot faces exceed 380 degrees, the metals will start to oxidise. You can very quickly shut off, the foam will collapse and pressure equilibrium Is restored within the boiler and you’ll have a visible water level (hopefully).
So we got a reverse osmosis plant! I won’t jump Into the science behind an R.O plant, but basically, the output water Is somewhere between 2 – 4ppm TDS, which Is Incredibly low. However, R.O water Is completely demineralised and It will seek to regain what’s missing by stripping It from the everything It comes Into contact with, which causes corrosion (counterproductive after everything I’ve just said, I know). From this, we learnt you need to blend, softened R.O water with raw water, to give back some of Its content so It doesn’t seek to take It from the boiler. The final result of all this long winded post, Is that the water at Rolvenden Is 4ppm hardness and 38ppm TDS and because of this, 376 Norwegian Is currently running at less than 1ppm of hardness In the boiler and you can run 14 – 16 days without blowing It down.
Unfortunately, 376, 4253 and 6619 are the only locos to benefit from the full force of the water treatment due to their water capacity (1800 – 2500gals) which means that can get round the whole railway and only take water from Rolvenden. The tank locomotives still have to get water from Northiam aswell as Rolvenden. Although Northiam has soft water plant, It doesn’t have an R.O plant, so because of that, the tank locos are running at 170 – 190ppm of TDS, but with very very little hardness. Because of this, we run a very high alkalinity (percentage of the TDS) and Ph of around 11.3 – 11.6 In the boilers to deal with any scale that does happen to form. The Ph stays at this level due to the chemical reaction of the water blend and water happens to the water In the boiler whilst under heat and pressure. We also feed Phosphate Into the boiler, but that’s a different story..............
There Is a direct correlation between TDS, Alkalinity and Ph, which means If you over blowdown the boiler, If the clacks are leaking and/or the boiler Isn’t water tight (not steam tight) the TDS will start to fall pulling the Ph down with It, leaving room for scale to form and corrosion to start.
I also get questions about tannin........the tannin Is merely there as an antioxidant In the boiler. It also contains a de-sludging and mud-forming agent to stop large deposits. It’s most effective at 100ppm.
There are an unprecedented amount of factors that affect all of this, but It’ll be overwhelming and If you’ve read this far, you’re mad. This Isn’t pure science, but more of a black art. I hated chemistry and alot of this Is waffle because I haven’t read It back to myself.
Here are some pictures of scale and tubes with their own story behind them..................Not sure I can add Individual descriptions to each one.You can also come and see them at the Rolvenden Museum of Random Boiler Parts."
"This Is just some Information and theoretical number crunching on as to why we have a water treatment plant on the railway and how It probably does more than you think and how It changes the dynamics on what happens Inside the boiler. Some of you may find this boring and some of you I could be teaching how to suck eggs, but It’s ‘marginally’ Interesting.....Depending on how you see It.
Before the water treatment plant was Installed, the railway filled the locos with raw water, with the water board changing the supply once a month or so depending on the time of year. These change overs still happen now and can cause chaos with predictions.
The current Incoming, untreated water at Rolvenden Is:
Total Dissolved Solids: 310 - 330ppm of which 160ppm Is Hardness, so In reality, the effective TDS Is 150 - 170ppm. Those figures are the same throughout the railway, with Tenterden being slightly higher In hardness.
On an average, our locos will evaporate one boiler full of water per trip and when the water Is evaporated, It leaves the TDS behind. So for every trip a loco does, 170ppm would be left In the boiler, multiplied by how many trips It would do, which Is normally three. This would leave 510 - 600ppm extra of TDS In the boiler per day ontop of what’s already In there. Your healthy limit Is somewhere between 1500 – 1800ppm and at 2000ppm, you will more than likely experience priming of some form. We use blowdown to control the level of TDS In the boiler and nominally, for every Inch of blowdown you do, you will lose 100ppm of TDS.
Example, If the boiler Is already at 1800ppm and It’s going to gain 600 throughout the day (Three trips) you’d blowdown 6” to make room for that gain.
HOWEVER, this does not take Into account the 160ppm of hardness you still have remaining. This will not come out of solution In the blowdown process and the railway was suffering from severe scale build up because of this. A running cycle for us Is 28 days, so over that 28 day period with three trips per day, you’d end up with somewhere between 13 – 20kg of scale formation within the boiler, which may or may not come out during a washout (13 – 20kg of scale Is easily two wheel barrows full, If not more).
If the hardness Is not dealt with and It reaches 350ppm, It will become supersaturated and It’ll start to form very hard scale. This will progressively get worse as It creeps beyond 350ppm. For example, a railway that will remain nameless, was accumulating nearly 70kg of scale In a boiler over the course of 28 days. This unfortunately went unchecked and started forming extremely hard scale and after being back In service for only two years, the crown and side sheets were removed from the boiler as It was completely scaled up and rippled the Inner firebox due to poor heat exchange.
In 1954, a loco on the London Tilbury & Southend Line had 4 tons of scale removed from It over the course of a year. This unfortunately didn't always come out during a washout and the boiler was frequently 'dismantled'.
So anyway, we Installed water softeners! Hurray! No more hard water and scale to worry about! But all of a sudden, the engines started priming to an absolute stand still and the TDS was through the roof! We learnt (the hard way) If you soften water, you’re removing the hardness, which means now, the entirety of the original 330ppm Is now problematic TDS and Is no longer removed from the equation. By fixing the problem of scale formation, we’d doubled the TDS gain per day and after two days of running, you’d already be at 2000ppm In the boiler. After three days, you’d need to do a water change. No degree of blowdown Is going to fix that level of TDS gain and If you let the TDS climb to 8000 – 10,000ppm, even If there Isn’t hardness present and the boiler was somehow only hours old, straight off the shelf (so to speak) It would start corroding. If you reach 15,000 – 20,000 you’d certainly be playing a risky game. The boiler of a locomotive In South America failed after only 8 months from new because of consistently running at 12,000ppm of TDS which corroded the metals. This boiler also had very little scale.
Another railway, which will also remain nameless, suffer from ‘Light Water’ which Is when the entire boiler content turns to foam due to bad water chemistry and very high TDS. Bubbles and foam will be visible In the gauge glass at this point. Because foam has almost no thermal properties, the temperature around the firebox and the tubes will suddenly start to Increase and If the hot faces exceed 380 degrees, the metals will start to oxidise. You can very quickly shut off, the foam will collapse and pressure equilibrium Is restored within the boiler and you’ll have a visible water level (hopefully).
So we got a reverse osmosis plant! I won’t jump Into the science behind an R.O plant, but basically, the output water Is somewhere between 2 – 4ppm TDS, which Is Incredibly low. However, R.O water Is completely demineralised and It will seek to regain what’s missing by stripping It from the everything It comes Into contact with, which causes corrosion (counterproductive after everything I’ve just said, I know). From this, we learnt you need to blend, softened R.O water with raw water, to give back some of Its content so It doesn’t seek to take It from the boiler. The final result of all this long winded post, Is that the water at Rolvenden Is 4ppm hardness and 38ppm TDS and because of this, 376 Norwegian Is currently running at less than 1ppm of hardness In the boiler and you can run 14 – 16 days without blowing It down.
Unfortunately, 376, 4253 and 6619 are the only locos to benefit from the full force of the water treatment due to their water capacity (1800 – 2500gals) which means that can get round the whole railway and only take water from Rolvenden. The tank locomotives still have to get water from Northiam aswell as Rolvenden. Although Northiam has soft water plant, It doesn’t have an R.O plant, so because of that, the tank locos are running at 170 – 190ppm of TDS, but with very very little hardness. Because of this, we run a very high alkalinity (percentage of the TDS) and Ph of around 11.3 – 11.6 In the boilers to deal with any scale that does happen to form. The Ph stays at this level due to the chemical reaction of the water blend and water happens to the water In the boiler whilst under heat and pressure. We also feed Phosphate Into the boiler, but that’s a different story..............
There Is a direct correlation between TDS, Alkalinity and Ph, which means If you over blowdown the boiler, If the clacks are leaking and/or the boiler Isn’t water tight (not steam tight) the TDS will start to fall pulling the Ph down with It, leaving room for scale to form and corrosion to start.
I also get questions about tannin........the tannin Is merely there as an antioxidant In the boiler. It also contains a de-sludging and mud-forming agent to stop large deposits. It’s most effective at 100ppm.
There are an unprecedented amount of factors that affect all of this, but It’ll be overwhelming and If you’ve read this far, you’re mad. This Isn’t pure science, but more of a black art. I hated chemistry and alot of this Is waffle because I haven’t read It back to myself.
Here are some pictures of scale and tubes with their own story behind them..................Not sure I can add Individual descriptions to each one.You can also come and see them at the Rolvenden Museum of Random Boiler Parts."
