End-Of-Main Traps

JoeC

Picture this in your mind if you can. A two-pipe steam system runs the 100' length of a ceiling in a garage area, with drips along the main steam to keep things dry. Somebody decided to remove the end caps from the steam and condensate mains, and replace them with reducing tees to add two additional unit heaters,'after the fact'. The system has been working absolutely fine, no hammering, no unit heaters filled with condensate, ect. Today an engineer stated that the two 'after the fact' unit heaters (added many years ago) now need to be equipped with 'End-Of-Main traps' to be piped in ahead of the unit heater supplies and teed back into the condensate returns from the individual unit heater. My opinion is the End-of Main and additional drips that currently exist, and which are ensuring any condensate removal from the steam main are adequate. And the piping that was added 'after-the-fact' were viewed by the old-timers that installed them as nothing more than additional branch lines. Any opinions today?

Steamhead

Is the return on this system

wet or dry? That is, does it run above the waterline (dry) or below it, so it's always full of water (wet)?

Brad White_2

Does the phrase

"if it ain't broke, don't fix it" apply? As stated, it has been working fine for years in this condition. Also, I would surmise that the "add-ons" pitch back to the "formerly end of main" drip trap assemblies, so they stay high and dry.

Normally in a 100 foot run, I would anticipate possibly an intermediate drip trap, right on the edge of thinking that and it depends on size of the main also. Just for that warm-up purge mostly. But that does not seem to be an issue.

I would say, absent any problems, leave it alone.

JoeC

It's a dry return. And yes, the additional take off do in fact pitch back and drain to the drip (original end-of-main trap). Once again, there is no hammering whatsoever due to condensate collecting in any part of this 40 year old system. It was my belief that 'end-of-main traps' are installed to remove any condensate that forms ,travels and collects down the pitched main (thereby eliminating hammering problems and such, nothing more, nothing less.

Alaska Joe

Your right on the money

If it isn't broke, don't fix it!

Christian Egli

venting

The end of main trap also serves to remove the air from the main on start up. Air from the branches and the units goes away through the trap on the unit.

The idea to get the air out of the mains specifically makes sense because mains are large in diameter, so there is lots of air to get rid of.

With that in mind, your main beyond the original end cap is no longer large in diameter and the venting aspect of it is similar to what happens in the other branches.

I understand no one is suggesting the orginal end of main trap should be removed. That, I think, would be bad.

Jacob Myron_14

end of main steam trap

If the system operates and causes no problems leave it be.

What I did not see written about was any reference to a condensate pump.

If a condensate pump is on this system you would need steam traps installed.

O by the way how is the system air removed because no one aske or stated anything about vent valves.

jake

JoeC

yes, all condesate is

gravity feeding to a condensate receiver and pump back down in the boiler room. All the traps that serve this system a re F&T traps with air vents. Are you stating that I should double trap the two add on unit heaters? (3/4" returns each)what would be the purpose of that? And is it standard practice to double trap branch lines to unit heaters?

Unknown

What hasn't been mentioned is condensate flooding

If there is a control valve on this unit that closes while there is steam on, the end of main trap will keep steam in the main up to that point.

Beyond the last trap on the main, and before the control valve, will have no such protection. As long as the steam is up, and that un-dripped section is valved closed, condensate will form and fill that main section. It has to. No way for air to get in, no way to dump the cooling condensate, no way to keep that section at steam temperature.

It'll fill. If there were any elevation change (obviously, there isn't here), it might be enough that the steam can't push the water through the control valve when it DOES open.

Ask me how I know....

(3 story risers that I put TRVs on each radiator, with no "top of the riser" crossover trap to vent air and keep the riser hot as the TRVs close. The symptoms were that the rooms that warmed first and satisfied would have no heat ever again until I shut off the boilers and let the steam pressure drop to zero. This let air back through the returns and into the supplies through the now open TRVs which broke the vacuum on the risers top and it relieved the steam pressure on the risers bottoms that held the water up there after it formed. See???

It took a while to figure out. The symptoms were exactly the same every day, but in different rooms each day in a 4 story building.)

I'd say, you got lucky on yours, if it works, and if it's quiet.

Noel

JoeC

No control valves whatsoever

these unit heaters have steam going through them the entire heating season. The fans are operated by line voltage thermostats....

Brad White_3

One would hope

that return line aquastats are used to control the fans when steam cycles down. These would be in-series to the power train of which your line-voltage thermostat is a part.

Hate to see wasted electricity over time. But might you consider adding 2-way non-modulating control valves? T-Stat would open the valve, strap-on aquastat proves temperature, fan starts.

Unknown

Why?

I hate to see over-engineering on something that works effectively and simply.

Low maintenance, and since the heat in the fan coil winds up in the space (that's the goal, anyways) with the fan off or on, and since a thermostat only calls on the fan when a "boost" in temperature is needed, this simplicity is perfect for the application.

A two stage heating effect on a budget.

It's fine the way it is.

Noel

Brad White_3

Not really over-engineering, Noel

For the maybe $100 to $200 in parts (depending if aquastat or both aquastat and control valve)and simple wiring logic, it equals appreciable energy savings.

If the steam runs the way he stated (all the time) then the unit heaters will act as radiators regardless of the space's actual needs. Sure, the T-stat turns on the fan, but standby losses can be a lot, and degrade the line pressure in the process. And if the space is satisfied, you spend heating money anyway.

Similar but extended logic would be to not insulate the piping, let it too be a radiator. Of course we would not do that, and the reason we offer is that we want heat where we want it (when we want it).

Nothing was said about the rest of the system and what controls that either. I took the scenario as this was one leg of several on a system. It may well be that this is the only distribution on the system, so your point would be well taken, keep it simple.

If a simple system (open-plan garage) then I would agree with you that the thermostat and fan control ought to be enough. But if in an isolated area, a partitioned area of the garage, then I would want to retard heat distribution -and conserve line pressure- by using a control valve and aquastat. JMHO

Tony Conner

Gotta Be Careful...

... cutting retrofit valves into existing steam & condensate systems. You need to watch the slope & trapping of these lines. You can get slugs of condensate forming ahead of closed valves. Then, there's the pressure issue. What's the operating pressure of this steam system? What is the setting of the safety valve that protects it? Lots of these systems run at 30 PSIG, which means that they fall under the definition of "high pressure". Others RUN at steam pressures under 15 PSIG, but the safety valves are set for more than that. Also "high pressure". Anything that you install on these piping systems needs to be properly rated for the application.

The current arrangement is very common - to the point of being standard - for warehouse loading docks, and garages that are fed steam from a central boiler room. It's simple, and works well. It also offers some freeze protection, in that the steam is never off - there's always pressure behind the condensate to push it out of the heaters and piping. It's amazing how fast some components full of condensate will freeze and split when exposed to cold air, when a big door is opened for a little while.

This whole initial recommendation to modify this system sounds like a "make work" project for an engineering outfit. It may not be exactly a textbook installation, but if it works OK, I'd leave it alone.

Brad White_3

Agreed

too many unknown variables. I stick by my "not broke, don't fix it" philosophy. But the fan control by aquastat may save some energy. Otherwise, leave well enough alone.

Unknown

How?

Quantify your last statement.

In this warehouse setting, what potential fuel savings would you realize by changing how fast you cool the fan coil after the thermostat satisfies?

Please be specific. You've alluded to this more than once now, and I disagree.

Noel