Steaming Minnie

[davidimurray]

After numerous years, building, meddling and procrastinating, I've finally got my Minnie to the point where I can steam it up, although so far I haven't had much success.

Initially I had a problem with the regulator not sitting square, combined with the boiler water frothing meant I ended up with a smokebox full of water that ran back down the tubes and put the fire out. Regulator sorted and a few more attempts, but I've been unable to get it above 15psi. I have previously tested the engine on air and it ran well.

I'm using charcoal soaked in Paraffin to get the engine lit. I've got an electric blower which I use on 6v to get the fire started, then switch to 12v to get it burning well. I keep adding more charcoal slowly and building the fire. I can get a good fire that is burning well, but I just cannot get above 15psi. There are a few small weeps from glands/fittings but nothing excessive.

I've ordered some coal grains to use as the charcoal doesn't seem to be doing the job.

Any help/tips gratefully received

[jma1009]

Hi David,

I refurbished a Minnie many years ago.

As you know, the boiler is really quite small.

I could get it up to working pressure, but the steam pressure would drop alarmingly and quickly as soon as the regulator was opened, and the boiler water would drop far more than I would have expected. The boiler was not a stable steamer. The amount of work on it I was asked to do was limited, and did not include stripping the cylinder assembly, but I did have a look at the regulator.

Something was obviously seriously wrong somewhere.

I dont think I have ever seen one working on steam.

Cheers,
Julian

[davidimurray]

Well we have some progress. After lapping in the regulator a bit, changing the balls in the pump, re-sealing a few flanges and getting hold of some proper coal I had another go at steaming her. The engine got to 35psi, she ran nicely, with a great blast up the chimney. Held pressure but the water level dropped quickly and despite running for 2-3 minutes with the bypass shut, the water level did not rise so I dropped the fire.

Before the next go I popped the cap of the pump and made sure the pump was primed and moving water. 2nd attempt I let her get up to 45psi, but on running again I couldn't manage the water level. The safety valves start fizzing from the off so I am going to pop nitrile balls in them. I think the steam I am losing as I build up pressure means the water level is low before I really get going. Might even try a temporary handpump to buy my some time to diagnose the pump issues.

[Roger]

Reading Julian's comments and the thread about Rosebud grates, it begs the question, would it work better with one of those?

[jma1009]

It is many years ago and I did not take much attention at the time, but the impression I remember of Minnie was of a badly designed traction engine that was really not much use other than as a display ornament.

Some traction engine designs in miniature have always seemed (to me) to have lagged some way behind miniature loco design, especially in boiler, cylinder, draughting, superheating, and valve gear design (there isnt much left out of this list!)

I would not expect to get much in the way out of performance from Minnie without a drastic re-design and updating.

Best to make a glass case for it for display?

Cheers,
Julian

[davidimurray]

Jun 24, 2016 22:28:02 GMT jma1009 said:

It is many years ago and I did not take much attention at the time, but the impression I remember of Minnie was of a badly designed traction engine that was really not much use other than as a display ornament.

Some traction engine designs in miniature have always seemed (to me) to have lagged some way behind miniature loco design, especially in boiler, cylinder, draughting, superheating, and valve gear design (there isnt much left out of this list!)

I would not expect to get much in the way out of performance from Minnie without a drastic re-design and updating.

Best to make a glass case for it for display?

Cheers,
Julian

What a disappointing response for a model engineering forum. I thought these forums were about discussing and encouraging model engineering. Perhaps I would be better off chucking it in the bin.

Minnie was designed back in 1969 and offered the model engineer the chance to build a small engine, with limited equipment. At the end of the day it is a freelance engine, designed to be simple to build.

In terms of performance what are you expecting? It is a 1/12 scale traction engine. In terms of size it is not much bigger than a lot of stationary engines, and what is the point of them as you don't get much performance from them....

There are plenty of Minnie's out there in steam and hundreds have been built over the years and have opened the door to bigger and better models and model engineers.

I will be carrying on with mine, getting over the teething troubles and enjoy steam it around the garden.

[kurplunked]

Please do post your progress.. I for one am interested in how you get on. I once had a Minnie for a short time and changed it in after experiencing many of the issues you are having.

[davidimurray]

Jun 26, 2016 20:41:34 GMT kurplunked said:

Please do post your progress.. I for one am interested in how you get on. I once had a Minnie for a short time and changed it in after experiencing many of the issues you are having.

Well she likes being in steam - link

Had a bit more of a play today. Changed the safety valves for Nitrile balls and they seal much better. Had her in steam 3 times during the day. Once upto 25psi she will start running and then the steam pressure rises rapidly and she starts blowing off. As soon as I start her running I have to open the firehole door to stop her blowing off constantly. She even had a little pootle around the patio under her own steam.

Best run so far has been 15 minutes continuously running in steam, before the water level dropped out of the glass. It seems that the pump is either not working properly or is not big enough. I wondered whether the optional anti air lock pin was restricting the flow so I removed it, but I haven't noticed any difference. I am thinking of making up an adaptor for a handpump as a test.

[kurplunked]

I seem to remember one of the issues o had with my Minnie was the lift in the delivery clack. The ball would lift and then block the passage into the boiler. I never checked mine against the drawing just messed around (can't remember what I did, sorry!) until it worked. Best of luck

[jma1009]

Hi David,

I am sorry if my posts were negative - which they were, but I can only post on personal experience of these things.

However, I am sure you will be able to make substantial improvements and fine tuning especially with your Ffestiniog Railway/Boston Lodge background and engineering experience.

I could just about get Minnie to run OK on a table as per your youtube link. I am pleased you have had a run on ground level as this is quite a challenge.

Cheers,
Julian

[runner42]

Hi David,

this forum's focus is helping ME builders overcoming their problems and Julian's track record shows that he is one of best providers of sound advice and often practical help, so don't be put off in continuing to seek assistance.

I personally have experienced similar issues as you in that a locomotive or traction engine that runs OK on air is not immediately going to be ready for steaming and running on its own motive power in a manner that you desire. As you have demonstrated that some designs are marginal in their steaming ability and require a bit more fine tuning and experience gained by the operator to reach their potential. You have to look at every aspect and work through them to improve matters if there is any doubt on their performance. You are doing that already and I am sure that you will achieve your goal. The forum's input is only to provide you some encouragement when frustration sets in.

Good luck.

Brian

[davidimurray]

Jun 27, 2016 20:02:01 GMT kurplunked said:

I seem to remember one of the issues o had with my Minnie was the lift in the delivery clack. The ball would lift and then block the passage into the boiler. I never checked mine against the drawing just messed around (can't remember what I did, sorry!) until it worked. Best of luck

I checked the delivery clack and both the one immediately after the pump and the one before the boiler seem to have a small lift but shouldn't block the outlets. What I have noticed though is that there does not seem to be a lot of water coming through when I turn the engine over by hand. On dismantling the inlet to the pump I've noticed the ball does not drop out, but has to be teased out.This suggests to me that the ball is lifting off its seat and sealing the pump inlet. It is made as per the drawings, but I think I may need to add something to prevent the pump inlet being blocked - possibly a pin to prevent the ball lifting high enough to block the inlet.

[chris vine]

Hi David,

Or maybe just some nicks in the edge of the hole above the ball. So even if it does lift, it doesn't seal....

Chris.