Pros/Cons Piston Valve and Balanced Slide Valve

A special section just for steam engines and boilers, as without these you may as well fit a sail.
lostintime
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Re: Pros/Cons Piston Valve and Balanced Slide Valve

Post by lostintime » Wed Nov 15, 2017 3:47 am

Injectors operate on the same physics as the educators I use regularly. Essentially you are using the cool water to condense the steam at the outlet of the first convergence nozzle to maintain enough of a pressure drop to maintain a "choked flow" condition. Essentially what this means is that you are accelerating it to sonic speeds (which varies with temperature). As pressure wave progression is limited to sonic speeds, it is a point that irregardless of increased pressure (under the same temperature conditions) that the orifice can not flow more than it is. The dynamic energy of this now condensed vapor is maintained as is its mass and therfore its kinetic energy. By then running it through a divergent nozzle to transorm this kinetic energy into pressure energy thus allowing the "work" to be performed in injecting your water. By increasng the orifice (thus mass flow) which will give you a linear increase, or better yet raising the temperature of of the steam (and thus the effective velocity limit which will give much better results) you can increase the available energy.. Id run the economizer after the injection point while feeding the ,injector with the hottest tap you have on your system. If you know the orifice size and temp its pretty straight forward to get to mass flow rate, speed of sound in steam at given temps is a well established and with that you can get to total energy available. Then work back from your boiler pressure (adding in your piping resistance) and see if it allows enough mass flow of make up water to keep your boiler happy.... Id vote try it, if it doesn't fire off plumb in a short superheat loop.
Last edited by lostintime on Wed Nov 15, 2017 4:02 am, edited 1 time in total.
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Re: Pros/Cons Piston Valve and Balanced Slide Valve

Post by marinesteam » Wed Nov 15, 2017 3:51 am

lostintime wrote:Injectors operate on the same physics as the educators I use regularly. Essentially you are using the cool water to condense the steam at the outlet of the first convergence nozzle to maintain enough of a pressure drop to maintain a "choked flow" condition. Essentially what this means is that you are accelerating it to sonic speeds (which varies with temperature). As pressure wave progression is limited to sonic speeds, it is a point that irregardless of increased pressure (under the same temperature conditions) that the orifice can not flow more than it is. The dynamic energy of this now condensed vapor is maintained as is its mass and therfore its kinetic energy. By then running it through a divergent nozzle to transorm this kinetic energy into pressure energy thus allowing the "work" to be performed in injecting your water. By increasng the orifice (thus mass flow) which will give you a linear increase, or better yet raising the temperature of of the steam (and thus the effective velocity limit) which will give better results. Id run the economizer after the injection point while feeding the ,injector with the hottest tap you have on your system. If you know the orifice size and temp its pretty straight forward to get to mass flow rate, speed of sound in steam at given temps is a well established and with that you can get to total energy available. Then work back from your boiler pressure (adding in your piping resistance) and see if it allows enough mass flow of make up water to keep your boiler happy.... Id vote try it, if it doesn't fire off plumb in a short superheat loop.
Or you could just say "it's magic" :-)
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Re: Pros/Cons Piston Valve and Balanced Slide Valve

Post by cyberbadger » Wed Nov 15, 2017 4:27 am

lostintime wrote:Id run the economizer after the injection point while feeding the ,injector with the hottest tap you have on your system.
Injectors will not pick up with hot water, at least not as designed for my Penberthy special high pressure model and Chicago injector on Nyitra. And I've never heard of this working. I mean, maybe you could bring it up to room temperature, but like above 120F on the suction line of an injector it's going to fail to pull a vacuum on the only moving part of the injector - the discharge swing check. And I'm not going to plug that. It's designed to protect the injector, and I've never operated my injector with that plugged. I plug it for filling cold. If I forget it the injector balks until I remove it.

In fact that's a common failure with very tiny (not mine) injectors in the hobby/small steam launch market. An injector can't get too hot or it just stops working until you cool it off. A temp fix is literally to dump cold water on it or place a rag with cold water on the injector.

I'm also not enlargening the injector nozzels, my penberthy is not a standard model - it's a special model that accommodates function up to my MAWP of 200psi. I had to make a special trade for it. And both of injectors have not had any issues and work so darn well. They only failed once this summer,

You should be able to guess why, it has to do with the location... ;)

Image

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Re: Pros/Cons Piston Valve and Balanced Slide Valve

Post by TahoeSteam » Wed Nov 15, 2017 4:33 am

Economizers are placed AFTER the pump or other source of water (injector)... therefore they will not be heating up the injector or the water going into the injector in any way whatsoever. The only potential issue I see is there may be too much back pressure due to the additional friction in the economizer, rather than the water going straight from the injector to the boiler.
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Re: Pros/Cons Piston Valve and Balanced Slide Valve

Post by cyberbadger » Wed Nov 15, 2017 6:58 am

Sort of answering my own question...

an Excerpt from "Injector Troubles: And How to Cure Them"
by American Injector Co Detroit Michigan
Deliver to Boiler. - Same size as injector connection. Large pipe may be used, but never smaller. Check valve "D" may be at any point between injector and boiler, the further from the injector the better. If the injector forces through a heater, place check valve between injector and heater. The stop-cock "E" is not necessary, but is a great conveinance when you wish to regrind or replace a check valve. A stop-cock is much preferable to a globe valve for such purposes."
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an Excerpt from "Injector Troubles: And How to Cure Them"
by American Injector Co Detroit Michigan
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Re: Pros/Cons Piston Valve and Balanced Slide Valve

Post by DetroiTug » Thu Nov 16, 2017 3:59 pm

Quote: "Or you could just say "it's magic" :-)"

Or you could actually have experience with one and know that some times when everything is right, they still don't work. They don't receive all those hammer marks from people checking if their hammer still works. :)
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Re: Pros/Cons Piston Valve and Balanced Slide Valve

Post by Mike Rometer » Thu Nov 16, 2017 5:50 pm

Oh yuss they do! :lol: :lol: :lol:
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Re: Pros/Cons Piston Valve and Balanced Slide Valve

Post by cyberbadger » Thu Nov 16, 2017 5:53 pm

DetroiTug wrote:Quote: "Or you could just say "it's magic" :-)"

Or you could actually have experience with one and know that some times when everything is right, they still don't work. They don't receive all those hammer marks from people checking if their hammer still works. :)
Nuck Nuck Nuck.

Once you take the time to understand them, you'll find that it is well worth the time to machine replacement pigtails (The 3 unions on almost every injector that get mangled or lost). I did that with my Chicago injector, which was made not 15 miles from here in Wadsworth Ohio. Buy Local!

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Re: Pros/Cons Piston Valve and Balanced Slide Valve

Post by lostintime » Fri Nov 17, 2017 3:10 am

DetroiTug wrote:Quote: "Or you could just say "it's magic" :-)"

Or you could actually have experience with one and know that some times when everything is right, they still don't work. They don't receive all those hammer marks from people checking if their hammer still works. :)
The first year and a half /two years I was running the eductors I had erratic performance. It eventually boiled down to to either the piping to convergence nozzle was to cold and vapor was condensing before the orifice (cured by adding a bypass line directly ahead of the inject flange to preheat the line), or heat conducting down the pick up tube preventing condensation in the mix chamber (finally solved believe it or not by adding fiber washers under the normal washers of the flange bolts to break the conduction path). It's now been over 5 years (knock on wood) since they've acted up. (175 psia:285F:NH3 V, 32 psig:17f NH3 L).
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