The Power of Steam – Part 2, by A.Y.


Monitoring and Maintaining the Water Level

Remembering the most important thing, which is Do NOT EVER let the water drop below the top of the crown sheet, there are sight glasses mounted on the backhead (rear) of the boiler to monitor the amount of water, and these must be watched constantly. Most boilers have two sight glasses; both are connected to the boiler at the top and bottom and have notches in the glass to help observe how much water is in the boiler. They also have drains on the bottom for cleaning out trash in the sight glass. These sight glasses must be cleaned by draining repeatedly before every start up and must also be blown down (drained under pressure) at frequent intervals during operation to ensure that the water level reading is correct.

Another set of tools that are used to monitor the water level in the boiler are called tri-cocks. These are a set of three valves found on the right side of the boiler (faced from the rear) that are set up diagonally, stepped down from each other. Before startup, the procedure is to open each of these valves and let water drain out to observe where the level inside the boiler is. Under pressure, the valves can be cracked open to observe if water or steam comes out. There must always be water coming out of the bottom tri-cock for safety. Likewise, there must always be water visible in the sight glass. If none is visible, do not fire up the boiler without adding water. If none is visible under pressure, do everything possible to add water in the boiler, and take the precaution of removing or dumping the fire out of the firebox to remove the heat. I cannot stress enough the importance of not letting the water level get too low in the boiler. On the other hand, too high a water level can cause a problem called priming or carry-over, which is when the water is so high it goes into the engine with the steam and can damage the internals of the engine. The trick is to maintain a water level where it can always be seen in the sight glass.

Now that we have covered the aspects of how to ascertain the level of water in the boiler, it must be discussed how to add water to the boiler. When the boiler is cold, the whistle or tallest fitting on the boiler can be removed and water poured in with a hose or buckets until it is at a good level in the sight glass. Also, a pump can transfer water to the boiler, if it is feasible. When the boiler is hot and under pressure, the use of injectors and duplex pumps are the most common ways to add water. There are usually two injectors found on boilers. These work by taking steam out of the boiler, rushing it through a nozzle to create speed, and shooting it back into the boiler. On its way through the nozzle, the steam creates a vacuum, which picks up water from a pipe underneath the injector and shoots it into the boiler alongside the steam. The water pipes that are connected to the injectors run to large storage containers that need to be kept full of clean water. These can be rain barrels, large tanks, and troughs or wagons specifically designed to carry water. Traction engines and railroad locomotives always carry a supply of water with them when they journey off somewhere. The injectors are amazing but simple devices and will work efficiently when the boiler is under pressure. However, since they work on the principle of a nozzle creating velocity from pressure, they will cease to work if the boiler pressure drops below a certain PSI. Every injector is different and will stop working at different pressures, so gaining individual experience with them is vital. Every so often, they must be disassembled and the forcing cone reshaped or rebuilt, because the steam and water erodes it over time. Also, there should be screens placed in the water pipes leading to the injectors to trap trash, and these need to be inspected and cleaned every day to keep an unobstructed flow of water. Another critical part of the injector is where it pushes water into the boiler, called a boiler check-valve. This works like a backflow preventer in a water line, and it keeps steam from reversing its flow through the injector. It is a good idea to inspect the boiler check-valves at the same time the injector is inspected.

When injectors fail or are not enough to keep a safe level of water in the boiler, a device called a duplex pump or boiler feed water pump comes into play. This is a device that takes steam pressure or air pressure and forces water in the boiler at a fast rate using dual sets of pistons that pump both backwards and forwards, instead of just one way. Duplex pumps have two steam (or air) cylinders and two water cylinders. They can also be hooked up to a pressurized air system, in case the steam pressure is incredibly low or unavailable. These have personally been life savers when the steam pressure drops too low for the injectors to work, and they must be inspected and cleaned every so often to maintain effectiveness.

Managing Impurities

Since we have now covered briefly the importance of water and how to add it in the boiler, we must insure that the best water possible is put in the boiler. Impurities and chemicals in the water can cause problems, such as scale buildup, corrosion, and foaming; these problems will eventually become serious issues that compromise the safety of a boiler. Scale is caused by impurities in the boiler water that concentrate when the water is evaporated and cling to the metal surfaces in the boiler. Most often called precipitates, these build up on heat transfer surfaces and interfere with important heat transfer to the water, lowering the efficiency of the boiler. If left unchecked and untreated, the scale can also prevent the water from keeping the metal surfaces cool, such as on the boiler flues; thus, hot spots can form that can eventually cause local overheating and rupturing of the flues, leading to failure. Some common feed water contaminants include calcium, silica, lime, and iron. This kind of water is commonly known as “hard water”, which is very common in many places. The first way to treat hard water is to try to remove as many of the impurities as possible, such as running it through a softener or water purifier. Once it is ready to be feed water for a boiler, a chemical scale remover should be added. A common scale remover is called Scale Gone 35 and can be found from various sources. Inquiring at local steam shows or automotive restoration stores should also give several ideas of where to find a good scale remover, as it is also used to clean radiators and copper piping. Instructions on mixing solutions will be available from the provider, and it is wise to every so often look inside the boiler when it’s cool to observe if scale is collecting on the steel or to see if the remover is doing its job.

Corrosion in boilers is also another dangerous occurrence and can be treated by using the correct feed water and chemicals. The principle of corrosion is the reversion of metal to its original form of ore. In boilers it is usually caused by high oxygen content in the water and a low pH balance. However, the problem of corrosion is one of the simplest to treat, in terms of boiler applications. A deaerator can be used in the feed water to remove oxygen, but the easiest way to remove oxygen from water is to let it sit in the sun in a large open top tank. As the sun shines down on the water, it draws the oxygen up and out of it, rendering the water less likely to cause corrosion. To determine the pH balance, a water testing kit is essential and can be found at any swimming pool store. If the pH balance is low, a simple addition of approximately 1 pound of baking soda per 5000 gallons to the feed water can be used to maintain a neutral pH.

Foaming can be another troublesome aspect of boiler operation. Foaming occurs when solids and other impurities in the boiler water cause bubbles to form on the surface of the boiling water. This makes it very difficult to ascertain the water level in the boiler and can fool some operators into believing there is plenty of water in the boiler when it is actually at dangerous levels. Like the other solutions to boiler water problems, one of the first steps to ensure there are no solid deposits in the water is to filter it before it enters the feedwater supply. While there is no way to absolutely be rid of all the solids, there are ways to eject scum and deposits from the boiler. Each boiler is equipped with blowdown valves, which are usually located on each side of the firebox, to purge the boiler of any collected solids and trash. The boiler must be blown down regularly to get rid of the deposits, and if the boiler is foaming, alternating the use of both blowdown valves continually can help stop the creation of bubbles and help the water settle down.

While the largest danger of foaming is not knowing where the water level is in the boiler, it can also cause a condition known as priming or carryover. This is when water clings to the bubbles formed in the steam and is sent through the steam piping (called a dry-pipe) to the cylinders. Since steam engines work on the principle of expanding steam, there are very tight tolerances in the cylinders. If water, being non-compressible, is allowed to get into the cylinders, it can be forced by the pistons against the cylinder heads and cause the cylinder heads to crack or be blown off, rendering the steam engine useless. Other things that can cause priming is carrying the water in the boiler too high and changing the load on a boiler very quickly. When the throttle is opened, only steam should flow through the dry pipe; if the water level is too close to the top of the pipe or the load is suddenly increased, the vacuum created by the steam can carry water along with it to the cylinders. The best way to gain knowledge of where to carry the water in a boiler is, once again, familiarization and a lot of experience.

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