Air Trap/Steam Trap design

This is an air trap from an air bottle drain. The valve is levered down (open) when the water level in the chamber floats the float; when the float is not floating, it levers the valve up (shut), see? fine.

Now, have you seen a steam trap with the same design?

I swear that I did somewhere, but when I sketched it on an exam last year I was accused of inventing things and marked wrong. (I got partial marks because my drawing “could” work, but not full marks because I was being imaginative.) From time to time I do invent things, that’s a fact. But I always take credit for my inventions, and I’m quite sure I have never invented a steam trap. Its a cute little thing, and I wish I had invented it. The marks are done and dusted, but I still want some vindication.


There are several float type traps … whoever graded your exam is a moron or a deckie.

Look at any of the Navy training books for fireman or boiler tenders or even machinist mate (if I recall correctly)

Or just Google marine steam traps.


I thought that if I found a drawing, that I could show my instructor that I wasn’t having a flight of fancy. I must have seen a drawing somewhere at some point. The only ones that I could find were of the type that has the valve on the chamber side, where it is leveraged to be up (open) when the float is floating and down (closed) when the float isn’t floating.

Like this:

Which he would have accepted. He’s neither a moron nor a deckie. He’s an experienced old-timer who may be a little crazy. We really like him.

Uh, that is what a float type steam trap does for a living. When the chamber is filled with condensate the float goes up and the valve opens to drain the condensate. When the condensate is gone the float goes down, the valve closes so no steam escapes … hence the name “steam trap.”

Some float types also incorporate a thermal element, some use a “bucket” that floats to close the valve then sinks to open it and drain the bucket which then floats until it fills again. That type has the outlet valve at the top of the chamber but the location of the valve itself is immaterial, its location is simply a matter of linkage.

If he’s an “experienced old-timer” then your drawing must have been a real flight of imagination.

The problem seems to be the type of valve used. I believe she drew one where the ball goes up and levers the valve down (open) and her instructor doesn’t think those ever existed. He believes the only kind out there are where the float levers the valve up (open).

Exactly so.

Except that today I opened one, it is fairly real.

Float type steam trap

Look at Fig. 13 and 14

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Devil’s advocate (and deckie here) but wouldn’t a valve down (open) run into issues with the steam pressure actuating the valve when you wouldn’t want it to? Again… deckie, so my steam plant knowledge is limited to the very brief time I had as a cadet doing my engineering crossover days.

Up, down, sideways doesn’t make any difference but if you meant seating with steam pressure then yes, you are correct, generally.

Of course, there are always exceptions and valves which seat against steam pressure are not unusual, the disc type trap is a good example. It is a matter of requiring the closing force to exceed the opening force when no flow is desired.

There is a bellows type trap also. When condensate is present, which is cooler than steam, a bellows retracts and pulls a valve off its seat, releasing the contents. When there is nothing left but steam, the valve seats again.

I should have drawn that one. Every bit as cute, and not nearly as controversial.

I was thinking about this question. There are probably hundreds of these things here, so why isn’t this a problem? I think its because the area of the valve that is seen by the inside of the trap is very small, while the area of the float is very large. If the trap was full of gas, with no liquid, the area of the float wouldn’t matter very much, because M. Blaise Pascal was a smart man. But if there was a little bit of liquid in the trap, the gas would have a net down force on the float. So I reckon the pressure of the gas actually helps to keep the valve closed.

I think a job in the deck or stewards department might be a better choice.

Learners make mistakes. Shoot down my answer and show me something. What’s your answer to jbtam99’s question?

What part of this post from 2 weeks ago don’t you understand?

your answer was cogent, but neither specific nor detailed for this particular one. Mine doesn’t contradict yours, and is specific.

If you want to take it personally, fill yer boots.

Trust me, your inability to understand technical concepts is not something I take personally. Your inability to comprehend fundamental concepts of physics and engineering subjects is neither my fault or my problem.

If you want to take it up with Pascal, maybe you can learn French and get a seance or something.

If you want to flame strangers on the Internet and display your unwillingness to mentor, then I’m so pleased that I could oblige. Please extend my condolences to your junior officers.