Steam Traps and Piping

[CharlieH]

Hi all....

My question is about the location of steam traps in a line. I realize its purpose is to release condensate while not releasing steam, but I have a particular circumstance that I can not figure.

Consider a 3/4" line coming off the top of an existing horizontal 3/4" 150# steam line and continuing vertically 12'.

The line then goes north (horizontal) about 8'.

It then elbows (west) and branches into (2) parallel 3/4" lines with block valve (still horizontal).

Each line then has a pressure regulator (150# to 80#) and another block valve.

Each line then changes to preinsulated 1/2" SS tubing and goes vertically about 30' to supply an eductor/heater combo and the other for blowback purposes.

Questions:
1. Do I need a trap assembly before the pressure regulators (before the branch to use only one trap)?

2. Do I need two more trap assemblies (one at the bottom of the 30' vertical climb on each line)?

3. Any tips on calculating the condensate load?

4. Can you recommend any books on steam piping? For that sake, what do you recommend for general pipe design? I have an older copy of "The Piping Guide" (Sherwood and Whistance 1st ed - 1973). Is there a newer edition with more info or just a new cover?

Thanks in advance for any assistance you can provide.

Sincerely,
Charlie

 

[TBP]

There tend to be two kinds of piping books - one that has it's focus on code related issues, and the other type will be oriented toward making the piping installation function properly. Spirax Sarco, Armstrong and others have a lot of good literature on how to install steam systems so they will work properly. They have very little info, if any, on applicable code requirements.

Basically, you need a steam trap at every low-point in the system, where condensate can collect. With a little functional design information & experience, you can minimize the the number of these. Remember that you shouldn't run steam lines dead level - they need to slope slightly, about 1 inch in 20 feet. Try to slope them so that the condensate will run the same way as the steam (forward slope). This isn't always possible, so sometimes you have to go with a reverse slope. Spirax Sarco's book "Hook-Ups" has a good explaination of this, along with a lot of other useful information, and diagrams.

 

[quark]

It is always better to trap steam line before a pressure regulator for better life of the regulator. When you split the flow after regulator, you can provide a trap for the common header. There are many free and good resources on condensate load calculation, pipe sizing and arrangement. You can visit the following links for a better understanding.

http://www.armstrong.be/pdf/N_101.pdf

Spirax Learning Center

PS: 11th chapter of the SpiraxSarco link deals with steam traps.

Regards,

 

[stanier]

The Efficient Use of Steam by Oliver Lyle and Steam Trapping and Venting by LG Northcroft & WM Barber are classic texts.

 

[TD2K]

I'd slope your 3/4" line upstream of the regulators enough that any condensate during low flow periods will drain back into the header. I wouldn't bother with a trap prior to the regulators. Now, if you brought this line down to grade and then back up, a trap off the low point would be a good idea.

I would also not trap the tubing downstream of the regulators if you should always have flow through the tubing. A lot of companies use 1/2" preinsulated SS tubing to supply tracing runs on piping. Typically, a 1" or 1 1/2" (your steam pressure is a factor here) comes down to a distribution header that is just a piece of vertical 2" or 3" pipe. Off this vertical pipe are 1/2" manifold valves which the tubing bundles are attached to. These are then run back up to the pipe rack and to the pipes they are going to trace. I've never see traps downstream of the distribution valves where the SS tubing goes up into the pipe rack. Now, you will have a trap off the 2" or 3" distribution header for all the tracers but your system's description doesn't have a low point as you do in the configuration I described.

After saying that, let me now waffle by saying the details of your your system has a lot to do with it. How consistent is the steam requirement that the 1/2" tubing supplying? If that tubing can sit for significant periods of time during cold weather, a trap to keep the tubing full of steam and not condensate which might freeze is a good idea. If the equipment that the tubing is supplying with steam doesn't want a possible shot of water, you might again want to provide a trap. As I said, a lot depends on your specific requirements.

Sizing the trap depends on how much heat you are going to lose from your system. I've found that most tracers don't use much steam, 10 lb/hr to 50 lb/hr seems to be a reasonable figure.