3 replies to this topic

[Rama]

Dear Majster,

Spirax Sarco have an excellent on line tutorials in Steam Engineering which you may try.
http://www.spiraxsar...am-trapping.asp

Please try also: http://www.spiraxsar...im-2-300-us.pdf where your specific worries are to some extent addressed. Water hammer is one aspect which needs to be taken care of. One way to mitigate the possibility is to provide another by pass to the ground drain (atmosphere) just before the bypass valve shown in your sketch. Open this briefly to remove the stagnant cold condensate from the pipe. However it is better to provide a second trap to be piped in parallel with suitable valving to allow one trap to be serviced while the other remains in operation, as suggested by Spirax.

Ram.

[Art Montemayor]

Majster:

I believe your system will work. However, I have some questions – linked to comments on the isometric piping sketch furnished:

1) Are you an engineer or a piping designer? The reason I ask is that the isometric sketch would be considered quite an “overkill” in design terms because the piping size is quite small. In fact, I don’t think you would find a smaller piping arrangement in an industrial environment. Since the sizes are very small (and so is the steam condensate flow rate), any hammering in the system would be very small as well and would, in my opinion, be contained well within the inherent mechanical strength of the small piping.

2) Since there is quite an effort made to depict the piping arrangement of the system, I want to point out that the isometric sketch does no seem to agree with the dimensions given. For example, the first condensate block valve is shown as being 727.5 mm from the elbow. This block valve is seen aligned with the bypass block valve (which is the typical arrangement done by piping designers. However, the length of the bypass run up to the bypass block valve is shown as 767.5 mm – and this run starts further downstream of the elbow. Therefore, by logic, the bypass run should be shorter – not longer – than the normal condensate run. I don’t offer this as criticism, but rather as an observation that the Isometric is not shown properly – if it is meant to be a true isometric.

3) If we are using the English language and its meaning, then the term “tubing” should not be used if, indeed, you are referring to piping. Your diagram mentions “29.7 mm internal diameter tube”. In the countries where the metric system is not the prevalent standard – as in the USA – the term used for cylindrical conducit is termed “pipe”. The term “tube” is another different conduit subject to different standards. Pipe is measured in its nominal size – not in the internal diameter. Tubes – or tubing – is always measured by the external diameter (“O.D.”). I believe the DIN standards in Europe also uses an analogous method to distinguish between pipe and tubes. The point here is that since the flow rate in question is so small, you might be able to employ tubing rather than piping – and maybe that is what you mean to state.

4) I would not recommend a ball valve as a bypass if it is your intention to throttle steam condensate through it should the steam trap fail. A ball valve is not meant – nor designed – to throttle. And if you don’t throttle correctly, you would exert a steam “blow-by” flow rate into the condensate system that would over-pressure the downstream system. I would not design for this to be a possibility. I believe it is better to install another steam trap in parallel as a stand-by spare trap in the event the first one fails. I normally have never used this principle personally because I never found my steam traps to fail. However, if your steam heater is a critical piece of equipment in the process and you cannot afford to shut down, then the parallel steam trap would be the safer and better way to go.

5) Also, you show a ball valve as the first block valve before what appears to be a control valve (certainly not a steam trap) and then a gate valve down stream. Again, why not use ball valves in front and back of a steam trap and use a globe valve to bypass around the steam trap? That, in my opinion would be more logical if indeed your intent is to throttle the condensate manually during operation (something I do not believe will work successfully or safely.

6) I would not use a 29.7mm inside diameter pipe (1” nominal size) in the vertical drain. I would design the vertical pipe to be self-venting in order to ensure that the vertical flow will be even and constant. If you are an engineer, you will know of what I am referring to. The Froude Number is an important term in gravity vertical flow and if the pipe is not in accordance with the Froude Number, you can experience bad results in the draining – even for relatively small flows like yours. I have posted an Excel Workbook on Fluid Flow in our Forums that explains this design technique and refers to a famous engineering article published some years ago with regards to gravity draining. You can download this workbook by using the SEARCH feature on our Forums and finding the workbook.

I hope my comments are of some help. Please do not take them as critiques of your design. I offer them as my experience in dealing with such systems.