loco won't run

Hi everyone, hope this is in the right place. We have a 3 1/5 gauge britannia loco.

It ran lovely for quite a few years and due to health and a move it sat idol. Just recently my hubby decided to strip the loco in order to get another hydraulic certificate. Reassembled and set on compressed air to check and it won't run, jyst blows straight out the chimney. Checked the pustons and gave her a clean and new grafite string, still not running. He wont ask for help but i hate seeing him so down after so much work. Ease if you could keep the answers fairly simple. I'm quite up to speed on steam but no expert. Thanks in advance.

Its probably easiest to diagnose in the flesh to be honest; are you near a model engineering society? My society is like most, friendly and keen to help. They certainly wouldn't like to see fellow model engineers in a pickle.

The 3.5" Britannia uses piston valves as I'm sure you are aware; these are another possible route for air to be escaping straight out the chimney without doing useful work. They are a bit more difficult to get to work nicely than slide valves, but efficient once working. 

My best advice is approach a club for help; we are all eager to get people into steam.

Jon (West Wiltshire Society of Model Engineers, and Westlands and Yeovil Model Engineering Society)

Edited By Jon Lawes on 09/11/2021 18:37:40

I would start by looking at the valves. I'm not sure if piston valves or sliding valves are fitted but if they have shifted then the air will bypass the cylinder completely and go out the chimney like you've mentioned. If the sliding valve has lifted and some thing has found it way under the valve you would also get this. This is of course assuming the reverser is in the full forward or backward position.

I would also check that the air is in fact coming out the blast nozzle (vertical tube that lines up with the chimney) and you don't have another leak in the smokebox that's blowing out the chimney bypassing the cylinders completely.

I very much doubt the problem would be with the pistons, you would need a large amount of blow-by for the loco not to turn on air.

BTW this is assuming the loco does move when pushed and nothing has seized.

Hope this helps...

thanks to you both, yes she has piston valves and as far as possible to see are working fine, obviously not easy to see inlet (inside inlet) but the exhust port is visable when the piston is in the correct possition. tbh the forward reverse has been one of those things i forget which way it should be for the forward motion. wound back towards the cab or full forward. i thought it was one of those back to front kinda things. We do have a society nearby and a member is also a member of our model boat club. Other than a that moving fine

Try getting up steam, oil up then try regulator and reverser, see if it starts to move. Hot steam works differently to compressed air. I understand that any compressed air blow through piston valve chest disappears under steam as cylinder oil and expansion due to the heat alters clearances.

First , a word of caution.

Do not use anything more than 10---15psi max. when trying to get the chassis running.

If it suddenly turns and your fingers are in there .......................it won't stop for those at 80psi.

If it worked before , it will work again , when valves/pistons are sealed and set correctly.

It's got to be something simple ! Depending on the degree to which it was dismantled will be a clue. If the air is from the chimney or blast nozzle that sounds like valve gear or settings. Has it got piston rings ? have they broken or stuck in their grooves ? If O rings have they broken. I'm presuming that all rotates freely if turned by hand ? Did your husband build it or buy it ready to run, setting the valves needs an understanding of how it all works to be set correctly. Good Luck and best wishes Noel.

thanks again everyone. J Hancock- yes appreciate that, always so careful.

Noel- he only removed the boiler. Running gear, pistons etc weren't touched, thats whats so anoying, it was running fine last time steamed.

DMB yes might be an idea, after all it is suppose to run on steam not air lol

He has now removed and put in new grafite string on the pistons just to be sure. Making sure to note postion and placement as not to disturb the settings. unfortunatley due to inside inlet it;s not really possible to deturmine the postion but like i said nothing had been moved. will keep you all posted

As Luker has said, is there a bad leak in the smoke box ! What about a crossed thread on the steam pipe from the regulator or if superheated from the headers ? A broken or misplaced gasket ? Noel.

Am I the only one to consider this all a bit odd? Hydraulic test of the boiler for what? To run the loco again, but where? A club track that it's boiler inspector will carry out the test? Yet no club is mentioned.

I could comment on other details provided that also seem odd. You wouldn't need to touch the chassis for a boiler test. All seems very odd to me.

Cheers,

Julian

The boiler hydraulic may have been carried out for peace of mind by the owner, If you have the gear it's easy to do ? If all the post are read it is stated that only the boiler was removed - so the frames and motion were untouched ! The loco belongs a gentleman who may not be in the best of health or frame of mind, his wife is trying to help him and thats what I and others are trying to do. Noel.

Hi Noel,

You might be right, but personally I have my doubts. Very happy to be proved wrong. I am pretty familiar with LBSC's 'Brit' design in 3.5"g.

As I said, it seems very odd.

Hi Noel,

You might be right, but personally I have my doubts. Very happy to be proved wrong. I am pretty familiar with LBSC's 'Brit' design in 3.5"g.

As I said, it seems very odd.

Hi Noel,

You might be right, but personally I have my doubts. Very happy to be proved wrong. I am pretty familiar with LBSC's 'Brit' design in 3.5"g.

As I said, it seems very odd.

Hmmm I think you may have mentioned that ........ Once or twice. Ever the diplomat?

Paul.

Julian, Just to put your restless mind at ease. We don't currently belong to a club. The hydraulic test was for peace of mind and yes just the boiler was removed all bar running boards which would have to be removed but definitely none of the running gear. Yes my hubby isn't in the best of health and yes the ever caring wife is trying to help. We built the loco together and would like to see it run again, all be it in the garden. Its definitely coming from the nozzle and no where else. All connection are all good.

Hi, Ive sent PM With some other ideas. Noel.

The following might help with the diagnosis:

First you need to make sure none of the linkages got snagged or damaged, and everything moves freely. With the reverser full forward (then backward) the loco can be pushed on a flat surface or track if you have. The wheels and everything should move freely. With the reverser in the mid position and the drain cocks open the loco should also move along happily. If the wheels get stuck open the drain cocks and see if the same happens (this would indicate a valve timing issue).

With the system under air pressure (15psi as mentioned), and the reverser in mid position – regulator open, close the blast nozzle with your finger. If you do have any leaks you’ll pick it up with this test (any leak you can hear is worth sorting out).

With the loco on a flat surface where it can’t run off a table and do damage, open the drain cocks, pressure the boiler to 5psi, and crack open the regulator in full forward. If you move the loco (forward) you should get sequential blasts from the drain cocks, then you know the air is getting to the pistons. If you don’t get blasts from all the drain cocks this is a good indicator the valves aren’t opening properly. The blasts from the drain cocks should be more or less at the end of stroke (slightly before with the older designers) from the drain cocks where the piston is. Make sure you have full control of the loco when doing this test.

Please let us know how you get along…

Thank you Noel and Luker, we will definitely keep you all posted and will try the suggestions. Probably won't be for a couple of days as hubby has been over doing it and isn't too well, so a couple of days rest.

Thanks again.

First question in my mind is whether the plumbing in the smokebox has been correctly reassembled. Seems odd that direct leak to blast nozzle should occur if valves and pistons are correctly set, which they would be if loco was previously running and none of the running gear has been dismantled.