Power Reverser questions

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Power Reverser questions

Post by Tank245 » Sat Feb 09, 2019 3:30 am

Hey everyone, have some questions regarding my power Reverser. I'm running a little Engines Mogul with a walschaerts valve gear and it has a working power Reverser. I purchased the engine used and the power reverser feed line was originally connected to the bottom of the sight glass and running on water. Naturally I wanted to get it off of the sight glass so I plugged the fitting and re plumbed power Reverser to a globe valve on the steam distributer in the cab since I have 3 open slots. I ran it on air and the power reverse worked much better than it did on water. On water, it was very slow and if you moved the Johnson bar to quickly it would seize up and you'd have to put it in neutral to equalize before putting it back in gear, on air it was very responsive and didn't seize up at all.

My question is however, being that water isn't compressable can I expect any gear issues if it's running on just steam? Such as the gear adjusting itself, or will the constant steam pressure be enough to hold the gear in place? (If you understand what I'm trying to say) anybody else have a power Reverser in their engines that could pitch in some info? My main reason for converting it was too stop feeding water from the sight glass, and keep the sight glass isolated.

Thank you!
Tim Parks

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Re: Power Reverser questions

Post by Asteamhead » Sat Feb 09, 2019 9:13 am

Hello Tim,
In case your reverser will work on steam reliable (piston rings, stuffing box and reverse valve), this maybe o.k.
Of course, speed is increased a great deal in regard to work on water! Maybe it's getting instable or creaping, cause there is almost no damping in this simple proportional steering :?:
I worked my power reverse on both cold / hot water, air or even steam (for test purpose).
The system works best and stable (but slowly, of course) on water fed from a bypass of the feedwater pump.
And look a video the way the prototype woks: Pretty slowly, to be handled with care!

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Re: Power Reverser questions

Post by hoppercar » Sat Feb 09, 2019 1:57 pm

Steam in the cylinder is eventually going to condense, and you will be back to having it moving on water pressure anyway

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Re: Power Reverser questions

Post by michaellynn2 » Sat Feb 09, 2019 2:55 pm

My loco has a power reverser and operates on water taken from a side sheet below the water line. Since the water is coming into the reverser under pressure from the boiler, I have not noticed "slow" motion of the reverser. The reverser does not get hot unless I put the reverser into forward and reverse constantly over a period of time.
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Re: Power Reverser questions

Post by Steve Alley » Sat Feb 09, 2019 10:07 pm

I have a customer that we change out his power reverse. One thing to know be very careful on just air that it can move so fast it will or can brake the valve shaft on the reverse head. I would have keep it on water pressure, Do to its just slower and more positive movement. But to store it in cold whether it needs to be inside a warm spot. You never can get all the water out of it, Like gauges.

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Re: Power Reverser questions

Post by michaellynn2 » Sun Feb 10, 2019 7:49 am

This is a very good point made by Steve. Since I operate my power reverser on boiler water, there still is water in the reverser cylinder during a boiler blow down. While there is little water in the boiler and lots of steam pressure, I run the reverser into forward and reverse to blow out the water in the cylinder. Once steam blows out the reverser exhaust, I know it is free of remaining water. For the winters nap, all the spaces are open to the atmosphere and the engine stays in a warm space.
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Re: Power Reverser questions

Post by johnpenn74 » Sun Feb 10, 2019 9:45 am

How are the prototypes set up?
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Re: Power Reverser questions

Post by FLtenwheeler » Sun Feb 10, 2019 9:49 am

johnpenn74 wrote:
Sun Feb 10, 2019 9:45 am
How are the prototypes set up?
They could be set up how ever the end user wanted. But I think most used air with steam backup.

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Re: Power Reverser questions

Post by RET » Sun Feb 10, 2019 2:02 pm


Two things to think about. First, in the Big Boy video I have, it takes about 5 seconds for the reverse unit to go from full forward to full reverse. Slow and deliberate, not fast.

Second, if you run a model locomotive while holding onto the unlatched Johnson bar with your hand, you can feel fairly strong forward and reverse pulses from the valve linkage as it moves back and forth. In full size operation these forces would be even stronger, but you never see movement in the linkage, no matter where it is positioned.

Both of these observations lead me to believe that in full size, the power reverse cylinder is full of water, whether it is from condensed steam, or water supplied from below the boiler water level.

Logically, in full size practice, you don't want the reverse linkage to move at all, since that will interfere with the engineer's control of the cut off which he uses to tailor the steam supply to the cylinders to match the power required at that time. A good engineer (either full size or model) would continually adjust the cut off as necessary to meet the changing conditions of speed, grade, etc.

Just what I've observed.

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Re: Power Reverser questions

Post by VGC » Sun Feb 10, 2019 3:54 pm

I do not know if I remember exactly, but I have the idea that there are two cylinders facing each other, one cylinder that drives the movement and one that slows down and stops it. It is possible that one cylinder is operated by steam and one is filled with water or perhaps oil?
It seems to me that operating with hot boiler water would lead to some remaining pressure, and operating only with steam or compressed air woul lead to elastic behaviour.
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Re: Power Reverser questions

Post by Miserlou57 » Sun Feb 10, 2019 5:42 pm

Power reverse almost always was exclusively air. Maybe they were piped for steam early on, but like steam brakes problems arise with the wet environment.

I suspect it’s possible some had some kind of steam bypass for emergencies, depending on the railroad’s practices, but I kinda doubt it.

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Re: Power Reverser questions

Post by michaellynn2 » Sun Feb 10, 2019 6:43 pm

The full sized locomotives used air on the power reverse. As the "Johnson Bar" is easily and slowly eased into reverse or forward the power reverser will catch up to the motion of the lever. Once the lever ("Johnson Bar") is eased into the desired position the power reverse locks the valve gear into that position. Once the locomotive is in motion the lever is moved back towards mid-position which conserves steam and reduces motion of the valves.
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