Plug valve overhaul

Has anyone had any experience overhauling bronze plug valves , the type typically used on blow downs etc. We have tried to overhaul 2 vavles, a 1/2" bore valve used as a whistle valve on AB # 1749 and the blow down valve fitted to Fowler #16342. The method we used was to machine the plug true then make an identical plug and wrapped fine sand paper to it and used this to true up the inside of the valve body. The 2 parts were then blued to check and reassembled. However they both leak ever so slightly so are not 100% tight. We would be interested to know any other ways of lapping these valves as information on there overhaul seems hard to come by.

Any help gratefully received.

Jason Durry
Silver Stream Railway
New Zealand

 

Could you post photos of the valve as I am not sure I understand your description.

 

I prefer something like pumice powder or the domestic 'Ajax' scouring powder for this sort of thing. Grinding/lapping compounds a bit too vicious for my liking. This assumes that the plug and body are a decent fit in the first place.

 

The valves in question look a little like this: http://www.heritagesteamsupplies.co.uk/Z-Heritage-Steam-Supplies/Blowdown-Valves/p-297-1175. A bronze body with a tapered plug that when rotated opens and closed the port that passes through the plug.

 

On AB 1719 I have a blowdown valve of this style. Assuming its not pitted and male and female parts are a good fit I have found that using grinding paste of various grades, finishing with fine gives acceptable results. I'm not saying that there might not be the odd drip from it. Tightness of the nut assists but can also make the valve very hard to operate. I do not use the valve as a blowdown when in steam but rather a method of draining the boiler.

 

Lapping with grinding paste is the way to go - just make sure you have the correct grade of paste.

 

Not heard from your project for quite a while. How are things progressing? You may have seen elsewhere that we have fitted AB1719 'Lady Nan' with new Gresham and Craven 5mm ones. Although they are the same injector size as the original AB ones they are physically much smaller. The big advantage is that they work well.

 

Sandpaper's fine as the first step, to get a rough fit, but as others have said, you need to follow up with a series of finer and finer polishing pastes.

Noel

 

Can you divulge the source of the injectors, assuming 'new' means new and not simply unused?

 

Things are progressing with 1181. It is a bit of a spare time project, gets pushed back when other railway projects take priority, currently have a carriage bogie undergoing a major overhaul so that's taking up a bit of time. We now have a new firebox on hand, made by Mendip Steam Restorations in Somerset. A fantastic job. The boiler is up on the newly fabricated trolleys, being cleaned down and assessed ready for repairs to start. I am aiming to have the repairs complete and hydro done by Feb 2019, in time for the boilers 80th birthday. Have done a few other bits and pieces, which can be viewed on the Facebook page, www.facebook.com/barclay1181restoration . If you are not a member of Facebook, you should still be able to see the pictures. What have you done with your old injectors? I could be interested in them if you have no further use for them?

Regards
Jason

 

@Steve - I sourced the Gresham and Craven injectors from North Bay Railway Engineering Services ( http://www.nbres.co.uk/ ). I believe that 5mm is the largest that they do.
@Barclay1181 - I still have the old worn out injectors. For the moment I am hanging on to them but at a later date I might be convinced otherwise.
Photo showing the old and the new:

 

Thanks for the response I've had mixed reports about those figure 4 injectors from North Bay but it sounds like yours are OK.

 

@Steve - I did have a problem with one of the body castings in that there was a flaw on the overflow boss that was only evident in use. It showed up as a fissure that went through the casting. As soon as this was pointed out to NBRES they did not hesitate to replace it with a sound unit.

 

I tend to make a dummy plug for grinding in. Only on the final lapping of the actual valve plug do I use the finest grinding paste the followed by a metal polish like Peak or Brasso.

 

Traction enginemen seem to speak highly of 'Timesaver' lapping compound, which is available from places such as Heritage Steam Supplies, apparently, unlike other compounds, it doesn't require cleaning off after use. I'm told that grinding paste and similar needs cleaning off with nitric acid, but I've no actual experience of it.