Steam & Excursion > ovefire jets

Some steam engines, like the D&RDW 1400s have overfire jets to help reduce smoke. Does anybody have details as to how they work?

I don\'t know if the 1400\'s had overfire jets but the explanation that was gave to me was the overfire jets were used to keep the smoke down when the locomotives were in the passenger sheds. Butch.G

I\'m not the worlds foremost authority on overfire jets, but I believe the basic idea is they are located down the sides of the firebox, and air is blown in through the jets over the top of the fire. This provides air to allow unburned gasses to cumbust cleanly. Something like the A.I.R. systems on many automobile engines where they pump air into the exhaust manifold near the exhaust port. This completes cumbustion of unburned gasses, reducing hydrocarbons at the tailpipe.
The principals or each are similar.
Mark D.

grande473 wrote:

> Some steam engines, like the D&RDW 1400s have overfire jets
> to help reduce smoke. Does anybody have details as to how they work?

Smoke is made up of unburned carbon and gases which are generally unburned because there is not enough oxygen present to burn them before they enter the flues and cool down below a combustion temperature. The overfire jets supply a secondary source of air above the fire bed to provide more oxygen to help burn this carbon.The jets themselves operate on the venturi principle, just like the blower. Each overfire jet has a small steam nozzle which shoots a jet of steam into a 2" tube which is installed in the legs of the boiler about 18" above the grates. the steam jet draws the outside air from outside the boiler and shoots it into the firebox above the fire. So instead of having to draw all the air needed through the grates, this secondary air inlet will help consume the excess carbon. The overfire jets were operated by a valve on the fireman\'s side when he deemed it necessary.It was designed to be used at station stops when you might have a lot of unburned coal in the firebox and no exhaust available to pull air through the grates. There were generally four to ten jets on each side of of the firebox depending on the size of the firebox.

Anybody have a photo or a drawing of these jets so that we can all have a better understanding of where they are exactly and how they are fitted (if that is the word to use) to the firebox?

I assume that oil burners do not have these jets because they are deemed unnecessary.

steamjocky

As stated they run up the sides of the fire box parrallel to the grates, AND are offset to each other from right side to left side to created further swirling motion inside the firebox from the cross action flow of air. Meaning that if there is one one the right hand side there isn\'t one in the same location on the left side, that one is set to the rear equal distance between the first and second jet on the right. This increases the amount of time the gasses have to burn as they are not just curling up over the brick arch into the tubes to suffocate out. They were developed to

A. introduce air to the firebox complete conbustion of fuel.
B. add burn time to fuel with the swirling action in the firebox that would have gone up the stack unburned
C. byepass having to draw air through the fire by introducing it above the fire and eliminating the further release of volitile gasses which would not be fully burned while in stationary location.


Oil burners don\'t need overfire jets as you can cut back on the fow of fuel and instantly reduce the amount fire. With a coal burner once you have a good bed made you can\'t shut it off and if you let it get to thin to reduce smoke there won\'t be anything left after the engineer opens the throttle and you would be really in trouble.

LLW 8673

here is a picture of canaster style jets on a 1700 DRG&W , some over fire jets were nothing more than a pipe with a nozzle sticking partway in the hole through the firebox

LLW 8673

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Thanks for the info.

I had not seen that style of canister overfire jets before. I usually see either the plain nozzle or "hatbox" style. Can anyone explain the reason for that unusual style canister on the DRG&W 1705? Thanks

I have never seen any first hand, diagrams of them or had a good explaination of that style of jet either. The Hat Style is such that was used on P & LE berks and the direct nozzle on NKP Berks. I\'ve always wondered what all that contraption is for but the D & RGW always had some very unique things on their engines.

LLW 8673

How many coal fired engines out there still running have overfire jets still in operation? I know that the CNW 1385 had them. There were discussions about the use of them. From what I could gather, the problem that some people had was that the overfire jets would bring in cold air and cause stress on the side sheets due to the cooler air coming in above the fire. Does anybody have any input on this either for or against using them now?

Thanks,

Ed

railbreaker wrote:

> How many coal fired engines out there still running have
> overfire jets still in operation? I know that the CNW 1385 had
> them.

Milwauke Road 261 was equipped with them, but during the initial rebuild in 1993 they never got reinstalled. The piping to them had been installed under the jacketing, but was removed during the most recent staybolt cap inspection. We looked at putting the jets back on a couple years ago, but found that over half the steam nozzles needed either some machining or were completely unsalvageble so the project was tabled.

I read that in some cases mufflers were applied to some over fire jets to deaden the loud hiss that they made. Perhaps these canisters are sound mufflers. We are pretty sure that they aren\'t air cleaners.