Injector
Injector
My e.e. standard injector worked great all day. But at end of the day, I couldn't get it to start ?... Found when I got home, my water piping to the injector,I could rotate by hand, meaning the nut on the injector water line was slightly loose. ...is this enough to keep it from running, and drawing in air ?........turning on the steam, I would just get a fast water flow out of the overflow......
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SPSteam2491
- Posts: 271
- Joined: Tue Feb 21, 2017 2:30 pm
- Location: Mukwonago, WI
Re: Injector
Yes, you are drawing in air.
You should also check the check valve going into the engine to ensure it is not stuck and would prevent the water from being delivered into the engine.
You should also check the check valve going into the engine to ensure it is not stuck and would prevent the water from being delivered into the engine.
Thanks
John LaFavor
Pacific Design Shops
John LaFavor
Pacific Design Shops
Re: Injector
It does not take much air. If my tender connections are not tight I hear a gurgling sound and get water out the overflow.
Re: Injector
Yeah ....I had that gurgling sound too .....like it was pulsing??.....but then I found the loose water line nut
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AnthonyDuarte
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Re: Injector
I responded briefly to Hoppercar on Facebook, but I think this is a good opportunity to go into depth on why vacuum leaks prevent injectors from working, and why minor leaks can cause high starting pressures. It may not be why you think!
When you're starting an injector below its maximum operating pressure, it is able to draw in significantly more water than it is able to inject, and injectors can only work when they're fed exactly the right amount of water. Remember, it's the weight of water added to the weight of steam that makes the output pressure higher than the boiler pressure. No other magic is involved. So the injector has to be fed at least the minimum amount of water required to make the output pressure higher than the boiler pressure, and if it gets too much water it overflows due to the limitations of the nozzle design. So it has to be in that goldilocks zone to actually inject. Where that goldilocks zone is depends entirely on the current operating pressure.
When you're below maximum operating pressure, the water valve has to be restricted to get the injector to start, because the gap between the steam nozzle and combining nozzle is big enough to let more water pass through than it can inject, so the water valve has to do all the work to limit the water. When the water valve is restricted, the pressure in the water line drops below atmospheric, and not because of the velocity of the water moving through the tube.
Imagine the water hose to the injector is disconnected and water is able to flow freely out of the hose at the exact rate of the injector's delivery. Now put 10-20inHg of vacuum on the hose (the suction force from the injector) and try to get the same delivery rate. You'd have to cut back the water valve to achieve it, and the vacuum has to be maintained in order to keep that flow rate stable. That's exactly what's happening when you have to cut back the water supply for the injector to pick up. The vacuum has to be maintained in order for the injector to receive a steady supply of the right amount of water. If there's a leak, even a very very small leak, the vacuum in the line builds and drops repeatedly, which is why a pulsating sputter is a clear indication that there is an air leak.
As the operating pressure increases, the injector is able to deliver more and more water due to the increased weight of steam per second, so eventually you get to a point where the gap between the steam and combining nozzle is restrictive enough to self regulate, and the water valve is no longer needed to get the injector to pick up. At this point, there is little to no vacuum in the water line. A small air leak is no longer detrimental at this pressure.
All this to say that if you have a very minor air leak, you will only notice it at lower pressures because that's when the vacuum in your line is highest. A micro leak might make it so your injector won't start until 60psi, a little worse and it may not start until 80psi, even worse and it won't start until 100psi. If it's not too severe, you may still be able to operate at max operating psi, and of course if it's too much the injector won't work at all.
Hopefully that ramble made sense!
Anthony
When you're starting an injector below its maximum operating pressure, it is able to draw in significantly more water than it is able to inject, and injectors can only work when they're fed exactly the right amount of water. Remember, it's the weight of water added to the weight of steam that makes the output pressure higher than the boiler pressure. No other magic is involved. So the injector has to be fed at least the minimum amount of water required to make the output pressure higher than the boiler pressure, and if it gets too much water it overflows due to the limitations of the nozzle design. So it has to be in that goldilocks zone to actually inject. Where that goldilocks zone is depends entirely on the current operating pressure.
When you're below maximum operating pressure, the water valve has to be restricted to get the injector to start, because the gap between the steam nozzle and combining nozzle is big enough to let more water pass through than it can inject, so the water valve has to do all the work to limit the water. When the water valve is restricted, the pressure in the water line drops below atmospheric, and not because of the velocity of the water moving through the tube.
Imagine the water hose to the injector is disconnected and water is able to flow freely out of the hose at the exact rate of the injector's delivery. Now put 10-20inHg of vacuum on the hose (the suction force from the injector) and try to get the same delivery rate. You'd have to cut back the water valve to achieve it, and the vacuum has to be maintained in order to keep that flow rate stable. That's exactly what's happening when you have to cut back the water supply for the injector to pick up. The vacuum has to be maintained in order for the injector to receive a steady supply of the right amount of water. If there's a leak, even a very very small leak, the vacuum in the line builds and drops repeatedly, which is why a pulsating sputter is a clear indication that there is an air leak.
As the operating pressure increases, the injector is able to deliver more and more water due to the increased weight of steam per second, so eventually you get to a point where the gap between the steam and combining nozzle is restrictive enough to self regulate, and the water valve is no longer needed to get the injector to pick up. At this point, there is little to no vacuum in the water line. A small air leak is no longer detrimental at this pressure.
All this to say that if you have a very minor air leak, you will only notice it at lower pressures because that's when the vacuum in your line is highest. A micro leak might make it so your injector won't start until 60psi, a little worse and it may not start until 80psi, even worse and it won't start until 100psi. If it's not too severe, you may still be able to operate at max operating psi, and of course if it's too much the injector won't work at all.
Hopefully that ramble made sense!
Anthony
Re: Injector
Very interesting....thanks for the input.....I must have had a micro leak with that loose water nut......it was loose, just enough, that I noticed I could rotate my copper line by hand.....it ran fine all day at the higher 120 psi.....but when shutting down on the steaming bays...at around 90 to 100 psi.....couldn't it to start.....only later at home I found the loose water line....but, I'm sure that was the culprit....
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Bill Shields
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Re: Injector
Hot cold hot cold ..things come loose...esp model unions.
Admittedly my injector success has been limited.. but I have had moderate success using tygon tube securely pushed onto the pipe from tender to injector then lashed on with twisted wire as a clamp...not very prototype...but something that provided visual clues as to the goings on.
Often when a normally successful injector started getting flaky...I would see air bubbles in the feed water....or heaven forbid what appeared to be the water running backwards into the tender.
Sometimes the visual clues are the most remembered... And to this date -> I hate unions on the feed to an injector.
Admittedly my injector success has been limited.. but I have had moderate success using tygon tube securely pushed onto the pipe from tender to injector then lashed on with twisted wire as a clamp...not very prototype...but something that provided visual clues as to the goings on.
Often when a normally successful injector started getting flaky...I would see air bubbles in the feed water....or heaven forbid what appeared to be the water running backwards into the tender.
Sometimes the visual clues are the most remembered... And to this date -> I hate unions on the feed to an injector.
Too many things going on to bother listing them.
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Howard Gorin
- Posts: 348
- Joined: Tue Jan 07, 2003 2:56 am
- Location: Waltham, MA
Re: Injector
Any suction leak is trouble and the suction leak may only happen under some conditions.
When I was building injectors I ran into an extremely exasperating problem.
My injectors would lift without any problem.
When they went from lifting water into the injector to actually trying to fill the boiler, the injector
would break, overflow and break again.
When my reference injectors which previously worked also failed on my test boiler I was perplexed.
After much searching and poking around for some reason I looked behind the flowmeter I used to measure
the injector delivery rate.
I discovered tiny bubbles at the top of the flow meter, only when the injector was actually trying to inject.
When the injector is lifting, the injector develops enough suction to lift the water, in this case about three feet.
When the injector begins to force water into the boiler much more suction is developed. between the water control valve and the injector.
The increase of suction drew a very small amount of air through a hairline crack in the body of the flowmeter.
As soon as the small amount of air drawn into the injector killed the injector flow to the boiler and the high suction
the injector would begin to lift again, try to inject, fail and try again and again.
The suction to lift water would not open the crack.
The suction developed when the injector attempted to inject would open the hairline crack
The hairline crack was from a stress riser in the plastic flowmeter body.
When I was building injectors I ran into an extremely exasperating problem.
My injectors would lift without any problem.
When they went from lifting water into the injector to actually trying to fill the boiler, the injector
would break, overflow and break again.
When my reference injectors which previously worked also failed on my test boiler I was perplexed.
After much searching and poking around for some reason I looked behind the flowmeter I used to measure
the injector delivery rate.
I discovered tiny bubbles at the top of the flow meter, only when the injector was actually trying to inject.
When the injector is lifting, the injector develops enough suction to lift the water, in this case about three feet.
When the injector begins to force water into the boiler much more suction is developed. between the water control valve and the injector.
The increase of suction drew a very small amount of air through a hairline crack in the body of the flowmeter.
As soon as the small amount of air drawn into the injector killed the injector flow to the boiler and the high suction
the injector would begin to lift again, try to inject, fail and try again and again.
The suction to lift water would not open the crack.
The suction developed when the injector attempted to inject would open the hairline crack
The hairline crack was from a stress riser in the plastic flowmeter body.