Drainage from a Steam trap - does it drain?

elfie

when replacing a very old steam trap below, a ton of water came flowing out from the strainer which means the steam main was filled with water. there is lots of pipe banging that was going on, which came from all the water.



the return piping coming from the steam trap goes up before connecting to a condensate return line



can this piping allow proper drainage??

Jamie Hall

That trap arrangement

is a crossover trap, or should be, and should have a drip to a wet return on the outlet, or on the steam main at the inlet.  The only way it could allow drainage would be if the steam pressure were high enough (which wouldn't be all that much actually) to push the water over.

elfie

drainage issue from a trap

this is a different view



is this a crossover trap configuration



seems that they may not be enough pressure to get water over the loop that connects to the condensate line after leaving the trap (the highest point on loop is in line with the steam main)



how can this drain properly?

Jamie Hall

I honestly

don't see how it can drain properly in that configuration.  Perhaps one of the wiser heads -- there are many on here -- can explain, but I can't.  I'd want to to see a drip connection...



Anyone?  Teaching opportunity here...

privyfire

trap drainage

You should probably have a check valve located after the discharge of the trap. 

elfie

condensate return pipe design issue

seems there may be a return flow issue.  trap was repaired and water flow doesnt quite make it thru to the main condensate return line



the high end of connection loop that connects to the main condensate line is at the same level as the steam main so water seems to be accumulating. as water accumulation in main increases, there may be draining, but no complete draining



can this be redesigned?  not sure a check valve would help???



thanks

Dave in QCA

larger system setup

The arrangement for this trap is very unusual for residential and small commercial gravity or vapor systems.  However, it is not at all unusual for larger steam setups in an institutional or process steam setups where the boiler is usually maintained with a constant pressure and other components provide temperature control.



I don't know how far this is from the boiler, so don't know what kind of pressure drop there might be.  But, from the settings you have indicated on the pressuretrols in the range of 2-5 psi, this trap will work fine.  As pressure comes up, it will hammer a bit until the water is pushed out.  A check valve on the outlet would be a good idea, but not totally necessary.



If you turn your boiler on and let it run, what pressure does it go up to?  What turns the boiler on and off?  Is it only controlled by the on / of switch on the burner panel?

elfie

condensate return problem - trap connection

boiler on/off is controlled by switch at boiler



there are thermostats controlling steam flow to rads (its a two pipe system, PSI is about 4)



there is no thermostat connection to boiler so mains are pressurized even when no heat demand exists - boiler is not turned on all the time



tough to see how pressure moves water thru the trap since the float mechanism would seem to neutralize impact of pressure.   seems its a gravity connection where the condensate pipe connection between steam main and the main condensate return line is always filled with water (so maybe a trap aint needed)



also, only vent in system is at the condensate vent pipe - so venting of system may be an issue if the looped condensate line is filled with water



any design ideas to get condensate away from the main steam line?



thanks

elfie

crossover piping from trap to a condensate line

in same system, here is another trap that has a crossover loop



how can this be vented when loop is likely always filled with water



on this trap the condensate line is dropping down from a higher level so there appears to be enough flow to push water over the loop (inside chamber of trap is likely always filled with water and float is likely always open)

Dave in QCA

drip leg through trap

In this set up, the water flows out of the main and down into the trap by gravity.  But it does not flow up out of the trap and into the condensate line by gravity.  It takes steam pressure on the steam side of the trap to do that.  You have 2-4 psi in the steam main, 0 psi in the return piping, vented through the condensate tank. If sufficient steam pressure is present, it will push the water through the trap and up to the condensate pipe.  When the trap is cold and empty, the Thermostatic section will be open and the float will be closed.  As steam arrives, the thermostatic section will close.  If water is present in the trap, the float will open until steam pressure has pushed the water out of the trap, at which time it will close.  The pipe between the trap and the return main will remain full of water.  That's not a problem.  The purpose of this trap is to let condensate drain out of a low spot in the steam line.



So, your system is designed to have pressure maintained once it is cold enough to need heat.  I am assuming that you have several zone valves to control the flow of steam into various steam mains in different parts of the building.  Or maybe each radiator has a control valve?  This changes a great deal in the way steam systems operate.  Also, if there are a number of other factors such as this lift trap setup in your system, The gravity steam rules that residential systems are usually designed by may not apply. 



You need to get a good pro in there to explain it all to you.



Or, another way to try to get a better understanding is to draw up a diagram of some type, that shows all of the various systems such as zones of radiators, air handlers, blast heater, that are connected to the boiler, and how they are controlled.  Some blast heaters stay hot, while a thermostate turns the fan on and off.  Other setups, there is a thermostate operated control valve.



The point that is clear with your system, is that it is quite large, and sounds like it has a combinations of different types of equipment or buildings connected to it that were built or remodeled over a long span of time.  To be able to answer questions about your system, we really need to have a better understanding of the whole thing.



As an example of why this is so, If one was evaluating the trap that you show in this thread, in the context of a residential type system where pressure is not maintained and where the boiler fires on a call for heat and may or not build any pressure, the answer is that it won't work.  That it is installed alll wrong.  But, in the context of your system, as you tell us more about it, it is just fine.  There are some absolute answers... such as "steam is hot" and "steam condenses to water", but for many other things, "it all depends" is the best answer.  It all depends on how the system is set up and how it is intended to operate.

Dave in QCA

Drip Leg

This trap is a drip leg trap.  Its purpose is to drain condensate out of a low spot in a steam main.  It will not function as a vent, that is not what it is for.



In most residentail systems where temperature control is achieved by turning the boiler on and off, and during the off cycles, the system fills with air, and then must be vented upon the next steam cycle, Venting is of extreme importance. 



However, in a system that is designed to hold pressure in the steam mains, venting is of little concern because the system is usually filled with steam.  As steam comes up and begins to build a little pressure, it will push the air through these traps, if the zone valves and other control devices are closed. 

Venting is so important on those systems, because it greatly affects even distrubution of steam under 0 pressure.   But, that is not how your system is set up to operate.  Should your system be changed?  Maybe, it all depends.  Would it save money?  Maybe, it all depends.  

elfie

drip leg trap - not designed for air venting?

in light of the need to lift condensate to allow draining in the above piping configuration, constant steam main pressure is needed



however, with the condensate line connecting to the trap being filled with water all the time, the thermostatic vent in the trap is not doing much in the way of air venting.  is this the case? and how would air get vented from system where this type of piping on condensate line exists.

Dave in QCA

Venting

Yes, you are right.  The trap will not vent at the same time it is filled with water, and for the most part, the thermostatic part will be useless.  However, if the system is cold, and steam is coming up.  If the control valves are close and the steam cannot push the air through radiators and steam coils, then belive me, as pressure builds, it will push the air through the trap, even if there is a puddle of water in the bottom.  Most likely though, is that control valves to zones will be open and the air will be pushed through the rads and coils.  It won't take long when you have 2-4 psi. and once the air is out, you don't need any venting until the boiler system is shut down.



I used to run a hospital building complex.  2   338 HP boilers, some direct fin tube steam heat, lots of air handlers with steam coils, steam to hot water convertors, steam blast heaters, steam sterilizers, domestic water heaters, on and on.....    Boilers maintained steam pressure 24/7.  In this very large system, there was not one single air vent device.  All venting occured through traps, through condensate return tanks.  There were many cases where the outlet of the trap traveled up 2 or 3 feet to the condensate return line.