[modeleng] Injectors

I know, an old chestnut!

I am babysitting a locomotive for a person who is emigrating, it is a 
7.25" 0-4-0 "Hercules".

I was at Swindon track yesterday with the locomotive for a boiler test, 
all was well until we came to the steam test. This locomotive has one 
injector and an axle driven pump, so both must work to pass the test.

We tried the injector and it refused to pick.  We changed it for a 
spare, which also refused to pick!

Tonight I steamed it up at home using two injectors from my Hunslet 
(both known to work) and neither refused to pick!

I therefore suspect that it is not the injector itself!

The operation was the same in all cases, water on, steam on, the symptom 
in all cases is excessive overflow.  There is a slight "twitter" as the 
steam is first applied, but that soon goes and the overflow continues. 
Adjustment of steam and water has no effect.

I have looked at the arrangements.  Steam supply is good.  Water supply 
is good, it is from balanced side tanks, 1/4" pipe and gentle curves.  I 
removed the water feed from the injector and it is running free.  All 
joints are tight and "air tight" as far as I can tell.

This only leaves the clack.  It certainly seals as there is no steam 
coming back to the injector from the clack (I swapped enough injectors 
with the loco in steam!)  I removed the top from the clack and all 
appeared well.  The only thing I could see was that the clack used to 
have a fibre washer sealing the top to the body. Only the remnants of 
the washer were left and the clack was sealed using PTFE tape. I don't 
consider the PTFE tape was causing a problem, but could the absence of 
the fibre washer reduce the lift of the ball to the extent that even if 
the injector wanted to pick, it couldn't get rid of the water fast 
enough, causing the overflow?

I am not an expert on injectors, so can somebody advise where to look?

Cheers

Peter





MODEL ENGINEERING DISCUSSION LIST.

To UNSUBSCRIBE from this list, send a blank email to, 
modeleng-request@xxxxxxxxxxxxx with the word "unsubscribe" in the subject line.

Other related posts: