Does anyone know why this loco has two sets of cylinders? Maybe something to do with the dual air reserviors?

There's a link below to a survivor that has a similar setup.

Homestake Mining No. 1A

mckay1995@comcast.net

> Does anyone know why this loco has two sets
> of cylinders? Maybe something to do with the
> dual air reserviors?

> There's a link below to a survivor that has
> a similar setup.

Compressed air locos frequently worked at extreme high pressures, 600 psi or more, and this made compounding possible. In the case of H. C. Frick 77 the tandem compound scheme was used. This was the most common scheme for underground locos, where a small profile was a benefit.

K3PRR@verizon.net

> Compressed air locos frequently worked at
> extreme high pressures, 600 psi or more, and
> this made compounding possible. In the case
> of H. C. Frick 77 the tandem compound scheme
> was used. This was the most common scheme
> for underground locos, where a small profile
> was a benefit.

As soon as I started reading your post, the light bulb went on and I remembered all of the times I've read photo captions that mention this-or-that steam locomotive having "cross-compound air pumps." I've read a little here and there about tandem compounds. Both cylinders look about the same size to me, so I hadn't even considered compounding as an explanation. Thanks for the info.



mckay1995@comcast.net

Are you certain that the air was in fact compounded? If it was compounded then the secondary cylinder would have to be larger in diameter to have the same work/force exerted. If not then the secondary air charge is not doing much of anything or at least not nearly the work of the first cylinder. Could this then be two cylinders sharing a common shaft and receiving air from the reservoir at the same time and same pressure? And having toured the Homestake museum The air locomotives displayed once were charged at 1000psi

> Are you certain that the air was in fact
> compounded? If it was compounded then the
> secondary cylinder would have to be larger
> in diameter to have the same work/force
> exerted. If not then the secondary air
> charge is not doing much of anything or at
> least not nearly the work of the first
> cylinder. Could this then be two cylinders
> sharing a common shaft and receiving air
> from the reservoir at the same time and same
> pressure? And having toured the Homestake
> museum The air locomotives displayed once
> were charged at 1000psi

A possible explanation is that both high pressure cylinders (smaller bore) are on one side of the loco and both low pressure (bigger bore) on the opposite side. Like a cross-compound steam loco times two. Perhaps someone out there has some literature on these air locos and could shed light on this.


K3PRR@verizon.net

Still doesn't make any sense. Running the exhausted air to the other side of the locomotive then invites further pressure drop. Look at some of the compound steam tractors. The low and high cylinder are on one shaft. This way the exhausted steam is already at the next cylinder. Of course that is a one cylinder steam example and may not translate to the air locomotive however I am thinking that if the air were used twice then it would not travel to the opposite side of the locomotive. I did not see any air engines at Homestake that had larger cylinders on the opposite side. Perhaps some of the Mechanical engineers around here could answer in.

I will throw my two cents into this interesting discussion. If you look at fireless steam locomotives, they were universally built with very large bore cylinders, even though they were charged to very high pressures (upwards of 600 PSI). The reason behind this was so when the charge was getting low, the locomotive could still do useful work.

I believe that this is a variation on the same theme, but since the locomotive is so compact and low to the ground, there wasnÂ’t room for two large bore cylinders, but there was room for four smaller ones.

SRC Mechanical Dept.
kelly@strasburgrailroad.com

> I will throw my two cents into this
> interesting discussion. If you look at
> fireless steam locomotives, they were
> universally built with very large bore
> cylinders, even though they were charged to
> very high pressures (upwards of 600 PSI).
> The reason behind this was so when the
> charge was getting low, the locomotive could
> still do useful work.

DELETED FIRST POSTING AND REWROTE IT.

I don't think they were compound because the compound design is intended to extract as much thermal energy from steam as possible. Compressed air doesn't have any thermal energy, in fact cools as it expands. In a fireless engine, the pressure decays relatively slowly as the water cools. The pressure in the pressure vessel is dependant on the temperature of the water assuming its still above boiling regardless of the amount of water in the receiver. So a single set of pistons is a very workable solution. But for compressed air, since the maximum traction effort is with a full charge and would decreases as the pressure in the receiver decreases. The cylinder size would be limited by the pressure in the receiver at full charge verses the driver adhesion to the rail. I wonder if they had a two stage piston set-up. IÂ’m guessing that some designated pressure, a valve opened or was opened to allow the second cylinder to receive air from the throttle in order to increase tractive effort again. This would allow the engine to work more near the limits of rail adhesion through a larger pressure range in the receiver.

Ed

ff1044@aol.com

This sounds like it would work if in fact it is what they did. This would be somewhat like a booster engine in that extra traffic effort could be used for a larger/longer set of ore cars. Using 4 cylinders would use available air faster and so only two would be used for economy. when more power was needed then air would be sent to the extra two cylinders.

Mining locomotives typically worked in very tight areas and a larger bore would not provide the necessary clearances for the power needed so tandem cylinders were utilized for the extra piston area needed.
Roger Mitchell
Master Mechanic: FCMRY

n0mcr@netzero.net