I am looking for information on running a Locomotive blower on air before there is steam. About how much volume and how much compressor motor HP would do the job? Some guidance would be greatly appreciated!

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If you have the use of a diesel locomotive, you can patch one of the trainline hoses to the air connection on your steam engine. Just open the angle cock and pretend you're charging the brake system on a long train.

At times we used a nearby diesel when not at the Museum shop.
We used a 150 cfm compressor there for the blower and to atomize diesel fuel til we had enough pressure to run the tank heater and switch over to No. 5 or 6 oil.
Brings it up nice and slow and the boiler liked it.
Early on, we burned a truckload of 2x4,2x8 and other fresh "ends" from the truss company outside the museum.
Not a good thing to do with an oilburner, but it raised steam. One trip we worked out of Lindenwood yard and up the hill after lighting off with the lumber. Incredible light show along I-44. After all the ash was gone, we sanded the flues. Quite a show that morning.
I don't recommend wood. After that trip, we put a tee in the oil line for using diesel to light off.
Steam days in a roundhouse, they had house steam lines for the blower, atomizer and heat the oil.

Just as with steam, it's mass flow and not 'pressure' that determines how many cfm at what pressure your blower 'wants'. Spec the compressor accordingly.

I'd use the lowest pressure that raises steam at the 'acceptable' rate to minimize thermal stress in the boiler -- how high this is will depend too on how 'primitive' the ring of nozzles in the blower is. The cfm will be that which allows you to maintain that pressure continuously with the compressor running. I'd recommend using a pressure tank, not as compressed-air 'storage' but as a means of maintaining smooth mass flow across compressor cycling, and smoothing any pulsations the compressor puts out.

Remember that compressed air chills substantially when it expands, and this may have an effect on the combustion gas spilling out of the stack. You can preheat the compressor output (with an arrangement similar to a lite version of the burner on a hot-air balloon).

I wonder if it would be cost-effective to 'historically restore' a steam generator like an OK-4260 and use it as 'house steam' for the purposes required...

At the WPRM in Portola, CA we use an 80 CFM rotary screw compressor for fire ups. It is large enough to handle blower and atomizer when firing up. The compressor never works that hard. I found that the Locomotive compressors worked, but the engine burned a lot more fuel than a diesel engine compressor. We usually from a cold start take about 2.5 hours to warm up and switch over in about 3.5 hours.

Watch the main reservoir pressure on the locomotive you are drawing air from. I have seen it where the steam locomotive was using air for both blower and atomizer and the compressor could not keep up the demand with the diesel engine at idle. The air pressure got too low to open the cooling shutters and the diesel engine over heated.

Good advice, but all you would need to do is throttle up a bit, just like charging a train. Center the reversor, cut off the gen field, and go for it. I admit this is a gas hogging method, but if you have a diesel you can use, there are conceivably circumstances where this would be most expedient or cheapest.

I really appreciate the advice guys, got some thinking to do. I have no way to set the throttle on our diesel like was described as its an air throttle and not a normal notch based throttle so unless i make a bracket that forces it to stay on that really isnt practical haha

Unless you also need air to atomize fuel in an oil burner, an exhaust fan on the stack should supply sufficient draft. We had that system at the NH&I when I was there 40-odd years ago, and I've seen it used at other places. (Just make sure the electrical cord has decent insulaton, no bare wires).

I haven't seen your diesel, so this might be a dumb suggestion: Try starting it with the angle cocks closed. Maybe you can throttle it up before cutting in the trainline. Maybe it'll run like that. Naturally I'd use the lowest throttle setting which maintains main reservoir pressure.

If that doesn't work, then it's borrow/rent/buy a portable compressor. One that can run a jackhammer should do it.

Colin,

The fan is a good idea since running a blower enough to just keep the cab clear of smoke will beat a compressor to death, again assuming you don't need air for atomizer etc