Plumbing 2 injectors

Hi All,

I am fitting 2 No3 injectors to my loco via one boiler inlet (Other boiler inlet is a hand pump) both have a NR valve on,Question is do i need NR inline valves on each injector outlet to stop back feed when one is working and the other shut down?

regards

007

Yes, you need a clack on each injector.

If the original clack is on the backhead you may be able to fit a double clack which would be a better option than two inline clacks feeding into the original. I did this on a loco I worked on.

John

Edited By John Baguley on 19/09/2014 11:13:13

JB - do you have a drawing fot that there double clack - me likes the idea!!

Yes a drawing would be good.

great idea

Might have been one of those things that I just made out of my head but I'll have a look back. It's basically just a brass block for the clack housing with a bronze spigot soldered in the back to fit the clack bush and two more threaded spigots soldered in the bottom for the pipe connections.

John

Hi John,

Thanks for the explanation of the Dual clack.

Does each clack have a seperate feed hole into the boiler or is it like a 2 into 1 arrangement?

007

No, just the one common drilling. IIRC think the back is drilled something like 1/4" diameter to take the threaded spigot that goes into the boiler and this drilling intersects both the ball chambers. I'm out at the club today but I'll try and knock up a quick drawing tonight when I get back. I've still got the loco at the moment so I can measure the clack for some dimensions.

John

Cheers John

Right, I've done a quick drawing with the major dimensions of the one I did but you can make it to suit: Hope you get the idea.

The body is a piece of rectangular brass bar, the two inlet bosses are also brass, in my case threaded 1/4 x 40. The spigot that screws into the boiler bush is bronze (I never use brass for bits that screw into the boiler) threaded to suit the bush. The balls are 3/16" dia. stainless or bronze. The holes for the ball seats are reamed and the bottom of the ball housing machined with a D bit or end mill to make sure it's flat. The caps are machine to allow the ball to lift 1/16" for injectors or less for pumps.

John

Edited By John Baguley on 21/09/2014 21:48:42

Fantastic John many thanks

Why is the lift different for injectors and pumps.This may explain why the clack i made for my engine pump rattles like a snake when pumped hard.

007

It seems to be the consensus that injector clacks need more ball lift than pump clacks and I have found this to be the case myself. The output from an injector is a continuous flow so once the ball lifts it stays lifted. The output from pumps is pulsing so the ball is continually opening and closing and tends to bounce around and may not seat properly between strokes if the lift is too great. This probably applies to axle pumps more than hand pumps where the pumping speed can be very high. I read an article in ME some years ago by a chap who had experimented with ball lift for hand pumps and found that in reality, very little lift is needed for a hand pump clack and the lift can be reduced considerably before causing any significant restriction in the flow. 1/32" lift for a hand pump is probably far more than actually needed.

John

thanks JB!!!