Higher pressure injectors

[ilvaporista]

Does anyone know of a source of reliable injectors that work up to 160 psi.? These are for a high pressure boiler on a 7 1/4" NG rack locomotive. Working pressure range needs to be from 90 - 160 psi. Most of the ones we have tried so far give up at around 115psi. Delivery needs to be quite large to keep up with the boiler output.

The loco works two Sundays a month near Naples on the only track in Italy that offers a regular steam service.

[chris vine]

Hi Adrian,

Since you already have an injector which gives up at around 115 psi, you may like to try an experiment of an old trick.

To raise the working pressure range of an injector you can try shimming the steam cone back (out) a bit. I don't know why it works but it has done when I have tried it.

The thickness of the shim will depend on the size of the injector and how much you want to raise its pressure and it may be that it will not give as much increase as you require. I would try between 2 to 10 thou to start with and see what happens.......!!

In your lovely sunny country you may also be having trouble because the feed water will be quite a lot hotter than we are used to here.

Chris.

[ilvaporista]

Thanks for the tip. The feedwater is from a tank on the trolley and is cold, I tried the old trick of flooding the injector from a hose pipe to keep it cool but still could not get it to pick up at higher pressures. Even with water direct from the underground storage tank stil no joy. The injector works fine until about 115psi then gives up.

I shall let you know the results of our experiments.

[greasemonkey]

Hi Adrian
The working pressure of an injector is a factor of its design. No matter what you try when it reaches its maximum designed working pressure thats it. Try doing as Chris suggests and moving the steam cone further back or else you will have to start from first principals and make a custom desinged item.
As a thought try giving one of the traction engine specialists a call. Some of the larger scale compound engines work at very high pressures.
Andy
Andy

[jackrae]

Adrian

Could it be that at the higher pressure the steam exiting the injector nozzle is achieving the speed of sound and effectively choking the injector. This is a common effect in control valves for gases whereby any further increase in differential pressure across the valve causes no increase in flow rate. The effect occurs in control valves when the nozzle discharge pressure P2 is equal or less than half the inlet pressure P1 (both measured in absolute terms).

However for injectors the pressure ratios could be quite different, never the less the effect will occur at some point.

If a supersonic wave is being created within the injector body then the ability to take up water is probably being frustrated.

Sounds like you may need a larger inlet orifice which in turn leads to larger injector body etc

regards
jack