Location of F&T Valve? Identity of Radiator Thermostatic Traps?

mpls2pipesteam · April 2023

I'm a homeowner with a gravity-return two-pipe steam system. I've been trying to determine how my system corresponds to this diagram from "The Lost Art of Steam Heating, Revisited":

I've found the main vents:

I don't see anything that resembles an F&T Trap though. The book seems to indicate that F&T traps are required on two-pipe systems, so I'm confused by their apparent absence. Could my main vents be doing both jobs? (For what it's worth, one of the main vents doesn't seem to be operational.)

Also, here is what the radiator inlets and outlets all look like.

I don't see any obvious thermostatic traps on any of the radiators, but it does sound like the trap functionality could be hiding in either the outlet, or the inlet. Is there an easy way to identify these components?

Thank you in advance!

JUGHNE · April 2023

You have 2 return pipes at the boiler. One of them is probably the dry return for the rad outlets.

The other is probably the end of a steam main.

Both should drop down below the water line before being tied together to the wet return just before the boiler.

Each are vented to remove the air.

Each have a water seal to prevent steam from getting into the Hartford Loop connection.

Your set up should not need a F&T trap.

Your radiator outlets may have some trap device inside to keep steam out of the dry return.

Or your inlet valves have an orifice to limit the amount of steam entering.

Or you are lucky enough to run as such a low pressure that all the steam get turned into condensate inside each rad.

Gordo · April 2023

Bit of a mystery there, because at least one of your "main vents" pictured appear to be for for hot water (i.e. a Hoffman 79).
Looks like both of them are hot water vents.

Many older types of two pipe steam or vapor systems don't (or rather didn't) have thermostatic traps at the ends of radiators, nor did they use F&T traps at the ends of mains or for drips.

Jamie Hall · April 2023

One would need to see more of the piping to determine which lines are steam mains and which are dry returns.

That said, most two pipe steam systems don't have F&T traps, nor do they want them. The diagram is of a slightly unusual variant. I would venture to say that your system may have originally been a very low pressure system -- a vapour system -- but I'd also guess that over the years changes have been made. If run on very low pressure, as they should be, and with the valves on the radiators set properly (or orifices used) there's no need for radiator traps, either. What there is a need for is copious main venting on both the steam mains and the dry returns.

JUGHNE · April 2023

If your system is piped as "my best guess" described above, then it is important that your air vents are both working.

The one on the end of the steam main would let steam fill the supply pipe quickly.

The one on the dry returns of the rad outlets would pass the air out of the rads for quicker heating.

It is possible, if the system is heating, that all the steam main air has to pass thru the rads to the dry return and slow down the heating.

In theory the dry returns could be vented with an open pipe as long as the rads are not passing steam thru their outlets. And both drops at the boiler are under the water line.
I would still put an air vent on the dry return as the perfect scenario seldom remains permanent.

mattmia2 · April 2023

Gordo said:
Bit of a mystery there, because at least one of your "main vents" pictured appear to be for for hot water (i.e. a Hoffman 79).
Looks like both of them are hot water vents.

Many older types of two pipe steam or vapor systems don't (or rather didn't) have thermostatic traps at the ends of radiators, nor did they use F&T traps at the ends of mains or for drips.

Are we sure this isn't gravity hot water? The radiator looks like it is set up for hot water (although it could be vapor steam with a modern valve replacing the vapor valve)

mpls2pipesteam · April 2023

Thank you all for your responses. They have helped me better understand our system. Here are a couple of photos that better illustrate our system.

@JUGHNE - My expectation is that the main vent at the end of the steam main (what I have labeled "A/B") ought to be venting while the boiler is running. Is that correct? (This is the one that didn't appear to be venting yesterday.)

When I observed the boiler yesterday, it seemed to be running at 3 lbs of pressure. (The tick mark for 1psi and 0psi seem to share the same location on the dial, so I was a little confused.) Here is a photo of the pressure gauge while the boiler is off:

Here are the Pressuretrol settings:

I think that these settings mean that the boiler is set to operate between 1.5 psi and 2 psi. Is my interpretation correct?

I'm not going to mess with any settings without a technician present, but from the information that I have provided, can you tell if our boiler is running at as low of a pressure as possible?

Thank you again!

mattmia2 · April 2023

That gauge isn't precise enough to measure pressure that low. Yo need to add a 0-3 or 0-5 psig gauge if you want to measure the operating pressure of the boiler. It looks to be set close to as low as that control goes. If you want what looks like a vapor system to operate properly you need it lower than that. It may not actually be building pressure, but you don't know without a gauge that is accurate at very low pressure.

Steam vents will only vent until steam reaches them, their job is to let the air out of the system so that steam can fill it.

mpls2pipesteam · April 2023

@mattmia2 - 100% certain it is not gravity hot water. I was told by the previous owner (whose dad bought the house in 1941) that the system is steam heat. And every week I turn off the thermostat, let the system cool down for a couple of hours, gradually introduce air into the system, and then flush out about a gallon of water.

ethicalpaul · April 2023

Why do you flush out a gallon of water every week?

And air is already in the system unless the boiler is currently producing steam...within a couple minutes after a call for heat, air comes back into the system.

Chris_L · April 2023

Am I viewing this piping correctly?:

- 2 boiler risers used with one-takeoff in between that splits into two mains A and B. No equalizer.
- Mains A and B reconnect at the ceiling and return to the boiler as A/B with vent at end.
- Another line (blue) returns to the boiler (radiator return?) also vented at end.

I don't know much about 2-pipe systems, but this piping arrangement seems odd to me.

109A_5 · April 2023

Hello @mpls2pipesteam,

Look at chapter 15, starting on page 381 of the "The Lost Art of Steam Heating, Revisited"
Also that main configuration in a loop like that may be problematic.
an I would agree the vent(s) may be incorrect of that application.

JUGHNE · April 2023

First picture is tricky. One boiler riser to header, one steam riser to 2 mains and then equalizer drops down.

The 2nd riser is capped and lines up with the equalizer, appearing to be connected together.

The rest of your description sounds correct though.

Mad Dog_2 · April 2023

Not ideal...Mad 🐕 Dog

mattmia2 · April 2023

Looks like the header from the old boiler is still there syndrome.

reggi · April 2023

@mpls2pipesteam
This return elbow "spud" ? looks a bit unusual with the flats .. perhaps improvised .. can we get a better picture of the connection to the radiator ?

Image: https://us.v-cdn.net/5021738/uploads/editor/dx/e1poi1pwawus.png

Mad Dog_2 · April 2023

To me, that looks like a Male Union. It looks way too short & close to be a close or butt nipple. Mad Dog

Jamie Hall · April 2023

Surely a union. Pink paint and all... which sort of makes me wonder if there might not be more to that "elbow" to the return than meets the eye.

mattmia2 · April 2023

I assume this has problems with banging unless the boiler is really well matched to the system because whatever may or may not be in those unions will have the steam blow right through it at the pressure that pressurtrol holds the system at.

mpls2pipesteam · April 2023

Thank you all for your input! I'm trying to better understand our steam system because we are going to be doing some remodeling that will require us to re-pipe about a quarter of the pipes in the basement. My goal is to figure out if there are any other changes that should be made simultaneously. In particular, we'd like to add some ability to reduce the amount of heat that goes to the second floor, but I'm reluctant to make any changes to the system without having a better understanding of what's already in place! I'll do my best to respond to each post. Thank you all again!

@ethicalpaul - I flush the system every week because that's what the previous owner told me to do. Having read through "We Got Steam Heat" just now though, I wonder if this actually is necessary? We have a Safgard probe-type cutoff, not a float-style cutoff. In "We Got Steam Heat", Dan says that float-style cutoffs should have their float chambers blown down every week.

@ethicalpaul - I should also note, because it might be relevant to @reggi 's comment that the system is under vacuum when during my flushing process. I have to very slowly re-introduce air to the system, which usually takes 20-30 minutes if I don't want to stir up the sediment.

@Chris_L and @JUGHNE - Yes, the second riser is capped. I was told by the technician that it would have been better if both of them had been used.

@109A_5 - What problems would you expect to see with our main configuration loop the way that it is?

@Mad Dog_2 and @mattmia2 - I think that we would consider re-doing the near boiler piping if there were benefits to doing so. Would re-doing the near boiler piping bring advantages other than being more logical and aesthetically pleasing?

@reggi, @Mad Dog_2 and @Jamie Hall - Here are some better photos of the outlets/unions on our radiators:

Looking through all of the different types of traps in chapter 9, our radiator outlets (traps?) seem to most closely resemble the "Richardson Three-In-One System" on page 428. Dan mentions that this system, "used a large float & thermostatic main vent at the end of each main. This tee-shaped device allowed air, but not steam, to vent. It came equipped with a check valve to keep the vented air from getting back in. As steam condensed, they got a vacuum." The only thing that doesn't fit with this description is that I don't believe we have any F&T valves, just main vents.

@mattmia2 - The system doesn't make too much noise. The radiators "tick" a little bit, but I've always just figured that is a typical expansion/contraction type of sound.

Thank you all again for your help!

mpls2pipesteam · April 2023

Here are the diagrams of the Richardson Three-In-One System from the book, if that's helpful:

mattmia2 · April 2023

It may be a richardson trap or it may just be a union elbow. The way the radiators are set up the system needs to control the amount of steam that is provide to the radiators by controlling the pressure and having some sort of orifice at the inlet of the radiators, either as part of a vapor type valve or with an orifice plate in the union at the inlet. If it is a water seal type trap it will only stop steam under pressure equal to the height of the seal, it won't stop a couple psig of steam like a modern steam trap will.

it is possible the boiler size matches the radiators and only produces as much steam as they can condense so it never builds pressure.

Jamie Hall · April 2023

You can see from the diagram in @mpls2pipesteam 's post above why I'm mightily suspicious of those radiator and union elbows. They look so innocent... and I'd almost bet they aren't.

All the more reason to keep the pressure very low -- that system is going to work best at around 4 ounces -- that's OUNCES -- per square inch.

Dan's mention of a "large float and thermostatic main vent" is quite correct -- no surprise there -- but just a little bit misleading. There is a tendency, I think, to suppose that he meant "float and thermostatic trep" or "F&T trap" -- which isn't the case at all. A float and thermostatic TRAP is a completely different beast -- with a completely different purpose -- from a float and thermostatic VENT. The best modern widget to replace a Richardson expeller -- which is what we are talking about -- is the Hoffman 76 main vent, or a combination of a Gorton #2 with a very low cracking pressure check valve to maintain a vacuum. Both of those are, in fact, float and thermostatic main vents, with the difference being that the Hoffman will hold a vacuum and the Gorton won't (hence the check valve, if you want to hold a vacuum).

There is some debate as to whether holding a vacuum is necessary, or just how beneficial it really is. In most cases, though, it will do no harm -- and if the system is holding a vacuum... if it ain't broke, don't fix it.

Now. On repiping. Be Careful and pay attention! Steam systems are, in general, very forgiving of odd piping -- up to a point. Beyond that point, however, even minor changes can result in the system working very poorly if at all. Maintaining the correct pitch of the pipes, and their relative elevations, can be critical. Before yu move a pipe laterally, never mind up or down, think very carefully how it is functioning now -- and how it will maintain that function after your proposed move. Their not like water or even sewer pipes, which can be rerouted quite casually.

JUGHNE · April 2023

I don't know if this is enough to discount the Richardson System or not, but your trap spuds are screwed into an eccentric bushing that is off center of the opening.

Other than that, maybe possible especially if you have good heating and no water hammer.

mattmia2 · April 2023

The way to reduce the heat to the second floor is to close the valve partially or add/change orifice plates to smaller orifices to reduce the amount of steam those radiators get.

reggi · April 2023

mpls2pipesteam said:

@mattmia2 - 100% certain it is not gravity hot water. I was told by the previous owner (whose dad bought the house in 1941) that the system is steam heat. And every week I turn off the thermostat, let the system cool down for a couple of hours, gradually introduce air into the system, and then flush out about a gallon of water.

If your system is truly under vacuum after a heat cycle your pressure gauge should go to 0 and at that point you can flip the lever on your pop off valve and you should hear the air being sucked in ( this won't stir up the water as this is all above the waterline )
Now you'll be at atmospheric pressure if you want to draw off some water..( as long as the pop off lever is open letting the system breathe, if it's vacuum)
Normally if your under vacuum and open your LWCO your shotgunning air right though boilers water as it's trying to fill the vacuum above the waterline with air... and that certainly stirs things up..😖

109A_5 · April 2023

Hello @mpls2pipesteam,

mpls2pipesteam said:
@109A_5 - What problems would you expect to see with our main configuration loop the way that it is?

The main in a loop configuration may trap air where you don't want it and cause balancing problems. However if your system is predominantly in a vacuum state there is a lot less air to be an issue.

Although I believe Hoffman 79 vent is not intended for steam service it may keep the system in a vacuum, which may have benefits.
"Hoffman 79 – Straight Water Main Vent Valve – 1/2" x 3/4. The Hoffman 79 Straight Water Main Vent Valve is designed for hot, cold, or glycol water mains in process applications with specific gravity greater than 0.7. With a pneumatic bell for discharging moisture"

Jamie Hall · April 2023

I'm not quite sure you are flushing out about a gallon of water every week. Unless you have a float type LWCO that is quite unnecessary, and just causes additional corrosion for the boiler. So why do it?

mattmia2 · April 2023

this is how your system works with different metering devices:
https://forum.heatinghelp.com/discussion/181572/dead-men-tales-the-model-k-mystery#latest

Mad Dog_2 · April 2023

My suggestion Sir....if u have not already done so....Purchase "WE GOT STEAM HEAT" So YOU understand and make sure the installer ATLEAST has a copy of The Lost Art..." to refer to. If you can get a good guy schooled on The Steam, that is ideal. Mad Dog

ethicalpaul · April 2023

@ethicalpaul - I flush the system every week because that's what the previous owner told me to do. Having read through "We Got Steam Heat" just now though, I wonder if this actually is necessary? We have a Safgard probe-type cutoff, not a float-style cutoff. In "We Got Steam Heat", Dan says that float-style cutoffs should have their float chambers blown down every week.

Don't do that

@ethicalpaul - I should also note, because it might be relevant to @reggi 's comment that the system is under vacuum when during my flushing process. I have to very slowly re-introduce air to the system, which usually takes 20-30 minutes if I don't want to stir up the sediment.

That's interesting. I'd like to see that. You aren't in Northern Jersey by any chance?

TonKa · April 2023

So, if I may sum up: you have what appears to be a relatively rare Richardson 3-in-1 system with questionable near boiler piping, questionable main venting (which may or may not be working), no low pressure gauge, and using a pressuretrol instead of a vaporstat. In spite of all past knuckleheading, it is still working fine (so you say).

Now, you want to change 1/4 of the piping in a home renovation.

I think you're pressing your luck.

All I can suggest is to make sure whomever is doing the work not only understands steam heating, but understands the rare Richardson 3-in-1, and is diligent enough to take the time to understand *this* system.

reggi · April 2023

@JUGHNE is correct.. without being on center the dip tube wouldn't be able to clear the nut/radiator when being installed. .

Location of F&T Valve? Identity of Radiator Thermostatic Traps?

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