What if any is the effect on the boiler from using air to drive a locomotive for short distances prior to a days running, say from out of the engine house. Does it matter the temperature of the water remaining or if there is steam present? Does oxygen content come into play? And last, does anyone else observe this practice?

I know of no reason why it would be harmful. Probably less stressful than steaming. I have run engines on air to blow out the steam passages prior to winter storage.

dave

We ran a fireless locomotive on compressed air. We put a lot of oil in the steam feed lines and pumped air tool oil in with the air compressor. Too much oil is good and when you fire with steam it has oil in it so it will clean out the excess.........fred

Lube oil from the air compressor may cause foaming of the boiler water when steaming.

Compressed air on top of water in the boiler supercharges the water with corrosive oxygen, 21 % of the air

That is what I thought, and fear. If anyone can address this further, I would appreciated it.

The first two wheel turns will get rid of the excess oil and let the engin operate in its own steam you must take care of the packing noving on air alone...fred

And the "surplus oxygen" in the water will boil out pretty rapidly.....although your water testing and treatment program can adjust oxygen scavenger dosing to compensate.

dave

As a retired chemist, and sometimes fireman, here's my take on the subject. Oxygen will dissolve in water; the amount that will dissolve depends on the temperature. Colder water dissolves more oxygen, boiling water will dissolve essentially no oxygen.

So, lets assume that you have water in the boiler when you want to move the locomotive with air. That water will be saturated with oxygen, based on its temperature, unless you have an oxygen scavenger in the water. When you pressurize with air, some more oxygen will dissolve, but it should be taken care of by your oxygen scavenger. If there isn't enough scavenger, some oxygen will dissolve, but not to worry, assuming you are going to light your fire the next day.

When heating up the boiler, your vent pipe should be open. Leave it open until you have a good solid stream of steam coming out for several minutes. That will get rid of any oxygen in the water and in the space above the water level. Then, close the vent.

An important reason to have plenty of oxygen scavenger in the boiler, is when you add water with the injector or feed water pump. That cold water that you are putting in will have oxygen in it. When it hits the hot water in the boiler, the oxygen will come out of solution. That hot oxygen is very reactive, and will be looking for somthing to oxidize. That should be your oxygen scavenger. If there isn't enough, the oxygen will oxidize the next available thing: the iron in the boiler steel.

I don't have enough experience in this area to comment on any effect oil from the compressor might have.

Jim Baker
Steam Foreman, PSRM

Hi JD, I visited with Roger a bit about this when I visited Alder Gulch July 4. At the SVRy in past seasons I know we have often moved 19 out of the shop on compressed air with no ill effects that I have ever heard about. We have never had a foaming problem due to oil from the compressed air that I am aware of, and I fired quite a bit for a couple seasons. If this were a concern due to a worn out compressor that was pumping oil, one could install a filter/seperator, or fix the compressor. My guess is like the other fellow said in that air that is absorbed into the water is driven off as soon as you start making steam. In the past at least we would leave a vent valve on the steam dome open until we were blowing steam out during a fire up. There is no doubt that water under pressure will absorb air as is the case with old domestic water system pressure tanks that became water logged, or hydronic expansion tanks in heating systems pre "diaphram type captive air" had the same problem. Based on the personal observation that it takes 3-4 months for an air charge to be absorbed in a large water system pressure tank operating at about 80psi, I doubt that the amount of air absorbed in the 1/2 hour or so a locomotive boiler is pressurized to move it out of a shop amounts to anything that could be detrimental considering the air will be driven out as soon as you start making steam. Just my unschooled opinion for what little it's worth. Regards!

I believe that if you are getting enough air oil to cause problems with your water you have major air compressor issues. A good separator should take care of that.

A bigger issue to me is how far are you going to move it and if you are going to move it on air have a way to operate the brakes either by charging the system or another means of providing braking effort. Another thought may be more effective insulation and reduction of any steam leaks. While I was at GCR we filled the boiler at night to a full glass of water and full pressure before pulling the pin on the fire. We typically did this at about 10PM. At 4 AM a morning crew would arrive and charge the air system with air and use the 120 to 140 psi boiler pressure to move the locomotive outside. They typically only lost about 15 to 20 psi doing this. By 4:30AM it was on its way back up to 200 psi.

GCR 18 water pump was good for putting valve oil into the boiler water. The locomotive liked to foam after a boiler wash but the addition of valve oil seem to calm it down. You may not have an issue with the boiler water and foaming.

Any element in the periodic table that is not a noble gas is going to react at some point with something What you want to do with your boiler chemistry is not make the Iron based components the preferred bonding partner. Iron is very stable in its oxide form so what the goal of an oxygen scavenger is to eliminate the oxygen from the boiler environment. Now remember that most municipal water districts add oxygen into their waters as a way to kill many bacteria. This Oxygen can reach your boiler if it is unchecked.

Robby

Robby,
Brakes are charged before any movement. We finish around 6:30p and have full pressure (150pi) and water before we shut her down. We fire again at 7:00a with around 30psi remaining on average. With this pressure we have no need usually to use air to get her out. If she's on "Low pressure dead center" that is one piston on dead center, other near cutoff, she'll not move so air will need to be used to get her out of her barn. Frankly we have concerns about the 02 when doing this. Our former method was a Plymouth switcher, but it had a suicidal back end so it's in the shop for an undetermined time. In the end we want to do what's best for the long term use of this engine.

Following up on JB's comments, like he said at SVRy we have used air to move 19 out of the Backshop to fire up outside (we have no exhaust hood in the Backshop). Once charged with air from a diesel compressor, the distance we move is so short, we kept the hose connected. We use the boiler air to run the steam compressor for air for the brakes.

Once outside, the boiler air is quickly bled off through a burp valve on the steam dome. The whistle is left open while firing up, and left open for several minutes as the water starts boiling.

We seldom use air, and it was only used when small diesel power was not available. Now we keep restored gas driven No. 100 behind 19 in the Backshop, and use it to push 19 out for fireup.

I was not aware that compressor oil is of a type that can cause foaming. Steam oil definitely will cause foaming since it is made from renderings (that is my understanding anyway).

We use Terilyn(sp) for boiler water treatment. I do not know if it has an oxygen scavenger in it or not, maybe someone here knows the answer to that question.

I would not worry about the rate of reaction of the O2 in the air source. Remember the formation is not a violent reaction like the oxidation of wood. Most boilers are already covered in rust so it will actually begin to impead the free O2 from reaching the iron. The O2 will disolve into the water but to reach the partial pressure in the liquid will take a while. This is where your oxygen scavanger will have time to seek it out and it will not be overwhelmed. Also remember that the air will initially settle in the boiler just above the water level as it temperature in the boiler will be less than the steam in the boiler. If after moving the locomotive it may be more effective to remove the oxygen from near the water's surface than from the top. I would not worry about removing it.
My thoughts.
Robby