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SOME MUSINGS ABOUT INJECTORS AND CLACKS
One of the most temperamental and troublesome items on a steam locomotive (and probably traction engines as well) is the injector. It can be working perfectly well one minute, then the next it doesn’t want to know, or probably has not worked really well in the first place.
Firstly if you have locomotive with side or saddle tank(s) then the chances if your injectors stop working then the cause is that the water has become too warm. For this reason I have a separate water tank on my driving skate purely so that cold water is fed to the injector. Chances are that apart from the residual heat from the boiler heating the water, clacks on the hand pump and/or the axle or cross-head pump are leaking and letting steam into your water (more about clacks later).
If the injector is not working the first thing is to check the obvious – has it been fitted the right way round !! The number of times at my club, problems with injectors have been found to be that they have been refitted the wrong way round after cleaning is quite amazing. In the photograph the injector on my Ruby can been, the steam pipe is on the left next the water pipe (short bit of pipe on the bottom of the injector) and the delivery pipe is on the right next to the overflow. In the photograph you can see a water valve not being used, originally it controlled the water to the injector but it constricted the water flow so much that the water is now controlled by the valve on the driving skate (a 15mm ISO valve). The valve was later used as a drain valve for the tanks but it was so slow that I disconnected it.
If your injector is not working or seems very reluctant, see if you can borrow a known working injector and see if that works on your loco. If it does not then the problem lies elsewhere. One the main areas is that the water feed to the injector is restricted, like using similar valves as in the photograph, try using an in-line type and larger piping from the water source to the injector, you can always throttle back if you have too much water. Also avoid tight bends in your pipe work, especially the water and delivery pipes.
Small particles like sand and ash which have a nasty habit of finding their way into your water tank can stop an injector working as the size of the holes in cones of the injector are not much bigger than a pin hole. If you suspect this is the case, then remove the injector and holding it up to some light see if can see through from the steam end to the delivery end. If you cannot see any light then your injector requires cleaning. I normally take my injector apart and pickle the bits in vinegar for a number of hours. It is import to remember which cone came from which end as they are different ! After the bits have spent their time in vinegar (or what ever pickle you use) wash the bits in water, making sure that the cones are clear, re-assemble the injector and refit to locomotive.
Now another culprit in preventing your injector working is the clack valve. If it is leaking the steam heats up the injector and it stops it working, dousing the injector with cold water can sometimes restart it. If the leakage is not too bad I simply leave the water feed on and this keeps the injector cool (another reason to have a separate water supply for injectors). I seem to have poor luck with the clack valves, as they all seem to leak by. I have replaced the injector clack with a new one a number times but no luck. One thing I did find is to locate the injector clack on the side of the boiler rather than at bottom of the backhead. Probably the water is less turbulent and chances are less for scale to get trapped in the clack.
Talking things over with members of my club (Northholt MRC, website www.northolt-mrc.org.uk) the consensus was that the ball seat should completely flat and not a cone. To this end I built my own clack as per the attached drawings. The main difference from commercial clacks is that the ball seat is removable as it is easier to make that way and also to be able to polish the seat with wet and dry. Having tried it out this season, there is an improvement but it still leaks by and I will try making the hole a bit bigger so that the ball sits further down in the hole.
Dimensions in inches unless otherwise stated. Material is brass.