Steam trap/return line mystery

Sailah

I come hat in hand seeing if anyone has an idea as to what I am seeing.

I believe I mentioned we are working on a steam trap monitor. I have a bunch installed at a university near here. I first went and tested using an ultrasonic tester and FLIR. Determined a bunch that were known to be failed. Or so I thought...

Installed monitors and let them go for a couple weeks. Recently I picked out a few to repair and did that. Here's my findings and question.



Monitor 87 was showing all the signs of failure. Sounded bad on ultrasonic etc. So I replaced it with a new faceplate and took the old faceplate back here to test. Tested fine. The monitor shows it failed wide open Christmas day, I replaced it on Dec 22nd.

You can clearly see when I replaced it, lasted 3 days and now is blowing again. My guys at the university confirmed it's blowing with their ultrasonic tester.



Things are different with monitor 92. Was showing signs of failure when I tested in place, continued to show signs of failure on monitor so I swapped it out. That trap is fine and verified. And it's all connected to the same piping.



There are (4) Sarco FT30 1.5" (blue arrow) traps trapping the large coils to the right in the pic. We believe some are failed and backpressuring the return line.

Looking at the gauge on the leg it looks like 0 PSIG but I don't know if it's on or pigtail is clogged etc. It also looks like there are check valves (white arrows) on those Hoffman returns.

I think the big Sarcos are bad or at least one of them is and it's pressurizing the return. I checked on our rack and 10 PSIG will easily blow past the seat if you hook the trap up in reverse.

So here's what I don't understand. I believe those Hoffmans have supply pressure at 13 PSIG even though the gauge doesn't show it. I need to verify this however. Because those are the supply lines to the coils it's dripping. But somehow the returns have more pressure than the supply and the Hoffmans are now reverse leaking. I verified that all pressure on the system from the power plant is 15 PSIG, they do not have any steam more than that. So how could returns have more pressure after going through a coil?

It's driving me insane!!!!

Steamhead

Maybe the supply line is going into vacuum. Put a combo gauge on there and let us know what you find.

EBEBRATT-Ed

Could you have failed traps elsewhere over pressurizing the returns?? Do you have steam blowing out of the condensate/boiler feed tanks?

Sailah

Steamhead said:

Maybe the supply line is going into vacuum. Put a combo gauge on there and let us know what you find.

Personally that's what I think is going on. I will do some further testing and see what I can find. It's a difficult area to work being a rooftop coil you can't just shut it off for an extended period. I may try to put gauges on that trap before and after. See if there's a differential.

EBEBRATT-Ed said:

Could you have failed traps elsewhere over pressurizing the returns?? Do you have steam blowing out of the condensate/boiler feed tanks?

There are def other traps failed. There are 4 1.5" traps and I believe at least two are failed. So those are dumping into returns. But say they are dumping into returns. How is it more pressure than the drip leg on the main? If anything it would be lower pressure.

The university did mention they are having a problem getting rid of condensate in that coil and it shuts down often. my first comment is let's rebuild those traps but at 15psig and get the larger orifice in the 15psi model. No reason to run 30psig traps on a 15 lb line. That may solve everything.

My theory is that the steam is whipping through there so fast it's creating a Bernoulli effect on the drip leg. Once that large trap dumps all the condensate in the return its finding the lowest pressure is going back thru drip trap.

But it's bothering me!