Situational Water Hammer

mattmia2

you could probably bring the cutout up a little higher since it is a trapped system to reduce the short cycling a bit and see if the water hammer stays gone.

is the 3rd floor radiator heating now?

109A_5

Hello @KarlW,
The Dwyer Photohelic won't help with the short cycling, just better control of the set points and differential. If all the radiators are hot at 9 Oz or less (assuming no other system issues other than a oversized boiler) you need a timer in series with the pressure switch to extend the burner off time. No point running the burner to make more additional, or maintain pressure, let the existing steam condense for a while, the added delay may satisfy the thermostat with less burner run time.
Something like this
https://www.supplyhouse.com/ICM-Controls-ICM203FB-ICM203F-Delay-on-Break-Timer-6-Wire-Leads-03-10-Minute-Knob-Adjust-Delay

KarlW

My venting does appear to be fine.

What's happening is that because of my smart valves, 1/2 of my radiators are closed on any given cycle. Combine that with my almost certainly vastly oversized boiler and I am just producing too much heat - especially on this 50 degree Christmas Day.

KarlW

109A_5 said:

If all the radiators are hot at 9 Oz or less (assuming no other system issues other than an oversized boiler), you need a timer in series with the pressure switch to extend the burner off time.

I have no doubt this would be the way to go, but the steam is very slow to get to all of my radiators at the current setting

Despite that, I am going to leave it as it is - I don't want to mess with the pressuretrol screw anymore, as I've found a working spot. I should be done short cycling early into the new year.

I am sure I will find a higher setpoint once the Dwyer comes in. Then if it short cycles I'll worry about it.

mattmia2

@ethicalpaul this is a 2 pipe system so the returns are only connected to the mains trough the radiators and the drips from the mains (in this system). There is no direct connection between the mains and the returns like in a 1 pipe system.

KarlW

@mattmia there is a connection between the supply and return at the end of the supply run.

It is where my two air vents are - see the pics above.

It seem it would have this to allow any water than condenses before reaching a radiator to return wouldn’t it?

mattmia2

KarlW said:

@mattmia there is a connection between the supply and return at the end of the supply run.

It is where my two air vents are - see the pics above.

It seem it would have this to allow any water than condenses before reaching a radiator to return wouldn’t it?

They aren't connected becasue they both connect separately below the water line. The water keeps the dry return and the main separate (or at least should).

This brings up another question about what happens to the vents in the return. The vents in the return won't close until they get hot from steam so if there is no steam in the returns which there should not be, the vents in the return never close. What happens when the equalizer tries to equalizes the main and the return? Does it keep putting steam in the returns until you get steam at a vent along with all the problems and sounds of steam in the return?

Maybe when there are no traps between the main and return but just a water seal you have to run at very low pressure

Perhaps @Steamhead or @clammy or @retiredguy can answer.

KarlW

My mistake, I misremembered where my supply and return connected - they meet under the water line.

Last night was the first quiet night in quite a while - I did have a trap to replace as well - discovered thanks to my smart valves.

clammy

Now aside from all the trouble shooting and guessing it comes down to a faulty pressuretrol. This really shows why having a 0-3 psi gauge is so important to have and should be installed on every steam boiler . I feel that anyone who is installing and servicing steam boiler and systems should have a test rig to test pressure and vapor stats especially the newer resido stuff right outta the box terrible .
To bad you can’t get anyone to really straighten out your near boiler piping ,the systems performance would improve as would distribution . A side note on gravity two pipe system which have no return boiler traps are generally ran at a pressure low enough to deal w whatever b dimension you have and a few extra ounces piping pressure drop .
Peace and good luck clammy

KarlW

Coming back to this, now that it has gotten a bit colder I still have a problem:

My boiler is calling for heat between 50 and 100% of the time and cycling on pressure. The best way to describe it is that the boiler is making too much steam.

Why do I say this? My lower wet returns are getting as hot as my steam mains and don’t cool down for a good 15 feet or so after the drop. As this is where the water hammer is, I assume that the return water is hitting steam in what should be the wet return.

My dry returns no longer have steam in them, that was an earlier problem I fixed.

I will check again the height, but I did earlier in this discussion and found my wet returns are well below the level of the water line unless my basement is somehow imperceptibly unlevel - previous sewer flooding pools so I am quite sure that is not the case.

What can I do to cool down my system?

EBEBRATT-Ed

28" of WC=1PSI rough rule of thumb

1 psi = 2' of head (rough rule of thumb)

1' of head is 2.31' of water

1" of head= 2.31 x 12"=27.72" of WC

mattmia2

That means at 9oz they have to be a little over a foot below the water line. where is the water line as some of the water moves out in to the system as steam and condensate where it reaches equilibrium?

You could try as an experiment raising the cold water level to close to the top of the sight glass and see if that extra height gets rid of your late cycle issue. if it does you know you either need to get those water seals lower, make a false water line at the boiler, or add thermostatic traps.

KarlW

@mattmia2 That was exactly it! I added water and it stopped.

Basically, there is a point that is still a couple inches above the low water cutoff where the boiler water level drops below the low return line, allowing steam to enter the low return and causing the obvious water hammer.

I had all this return replaced two years ago when it corroded through and I guess the installer sloped it a little to high. It wasn't caught during testing because you would tend to test at a normal-full water level, not a below normal water level (in other words, I don't particularly fault the installer here).

My boiler water line is nominally 10" above the low (wet) return. I am going to try to adjust the pipe stands and even turn the elbow at the drop to try to lower the corner point of my wet return and inch or two.

This leads me to the following question: what is the no boloney minimum pipe slope I can get away with? I assume that the design is 1/4" per foot standard for drainage, and we are talking a 40-50ft pipe run - can I reduce to 1/8" per foot (more like 3/16" or 7/32" over this distance) or would a false water line be the better choice?

Or could I put a thermostatic trap on the line at this point - is that what you mean? What product and size would I use?

Remember I still can't find a true boiler mechanic in WNY and will likely be doing this myself.

mattmia2

Others can correct me if i'm wrong, but wet returns don't need to slope, they can even go up and come back down as long as they stay below the water line, the water will still flow through it. I would probably just get the drip as close to the floor as possible.

If you use a trap you need to know about how much condensate flows through it. I suspect a radiator trap would be sufficient in that application. There are vertical versions that have a top inlet and bottom outlet.

There are also schemes to add more volume to the boiler externally with some large piping.

KC_Jones

Sloping a wet return on replacement was the mistake. Water seeks it's own level so slope on a wet return is not needed, it's not hurting if its there, except for what you are currently experiencing. Good possibility that an older boiler had a much higher water line and any slop that was there didn't matter as it always stayed wet.

KarlW

So from this pic you can see the results of the work I had two years ago after the 100 year old original iron pipes corroded through.

The steam supply drop is on the right while the dry return is the 45 degree pipe on the left. In this photo you can see where the original pipe ends and the new pipe begins.

Most importantly you can see the large pipe support they installed, providing the unnecessary support.

They will come back Tueday to look at this. It’s been two years but I am going to insist that they do it under warranty.

To be sure, does the return pipe typically flow full or only partial? I assume only partial as that would be the key to return with no slope.

mattmia2

What do you mean by flow fully? There is just a trickle of condensate in those pipes, more from the actual return since it is all the steam the radiator(s) condense but the drip from the main only has whatever steam condenses on the walls of the pipe.

It could even go down to the floor where they connect and come back up with an ell to the return, the low section will trap water to keep the steam from blowing through.

I'd have then put a tee and an ell and a cap or boiler drain on the end so you can hook a hose up to it to flush out the return.

You can do that in copper too, doesn't have to be black iron for a wet return.

KarlW

mattmia2 said:

What do you mean by flow fully? There is just a trickle of condensate in those pipes, more from the actual return since it is all the steam the radiator(s) condense but the drip from the main only has whatever steam condenses on the walls of the pipe. It could even go down to the floor where they connect and come back up with an ell to the return, the low section will trap water to keep the steam from blowing through. I'd have then put a tee and an ell and a cap or boiler drain on the end so you can hook a hose up to it to flush out the return. You can do that in copper too, doesn't have to be black iron for a wet return.

I just mean that the pipes don’t flow full of water, but knowing that the wet return isn’t pressurized, it answers my own question.

I do have such a trap at the end of my line, it goes into a cut in my basement slab through dirt. 

The good news is that I  do have that cap at the end (on the other side of the trap where worst case I could a vacuum).

I think further up I have pics of both of these.

The black iron and slope for that matter are an indication of the lack of true residential steam professionals in Western NY. This is by far the best company I have worked with on this and they didn’t offer a copper option (I wouldn’t have taken it) and they assumed the low return needs a full slope.

mattmia2

Just to make it clear, where the 2 pipes connect to the wet return needs to be low enough below the water line that they are still below the water line with the pressure in the main pushing down on the column of water in the riser to the main. Those 2 horizontal tees need to be as far down as possible because the water in those risers and the bottom of the return is what allows water to flow out of the main but keeps the steam from following that pipe in to the return.

I think you understand this but I just wanted to reiterate.

109A_5

Hello @KarlW,

KarlW said:

Coming back to this, now that it has gotten a bit colder I still have a problem:

My boiler is calling for heat between 50 and 100% of the time and cycling on pressure. The best way to describe it is that the boiler is making too much steam.

Why do I say this? My lower wet returns are getting as hot as my steam mains and don’t cool down for a good 15 feet or so after the drop. As this is where the water hammer is, I assume that the return water is hitting steam in what should be the wet return.

My dry returns no longer have steam in them, that was an earlier problem I fixed.

I will check again the height, but I did earlier in this discussion and found my wet returns are well below the level of the water line unless my basement is somehow imperceptibly unlevel - previous sewer flooding pools so I am quite sure that is not the case.

What can I do to cool down my system?

I still think you are chasing system symptoms caused by adding the European smart valves (which have the negative effect on the system by reduceing the connected EDR at any given time, so yes, the boiler is making too much steam for the available EDR.

"My boiler is calling for heat between 50 and 100%"
I'm at about 43 degrees North Latitude similar to you and similar temperatures. At 30 degrees Fahrenheit my boiler runs very close to 38 % duty cycle. Is your thermostat in the coldest room ?

The pressure ends up going too high due to extended boiler run time and reduced EDR so steam gets to places it should not normally be, causing other problems.

IMO you don't need the pressure, (my 2 story house heats fine at less than 1.0 Once pressure) however you may need the extended boiler run time to heat the third floor. It seems with your system the result of the run time is pressure due to the diminished EDR (European smart valves, maybe an oversized boiler too). I wonder if the steam pipes to the third floor are poorly insulated and/or near cold outside walls, so if the heating cycles were more normal the steam headed that way is constantly have to re-warm exceptionally cold pipes before it even gets to the third floor, which takes time to do. In your case time (poor duty cycle) equals too much pressure which causes other system issues.

Also (I think this was previously mentioned) if steam is getting to places it should not be (due to pressure) it may be trapping air, so a situation like this may also inhibit the third floor or other radiators from heating properly.

"What can I do to cool down my system?" Limit the pressure and the boiler run time (get the duty cycle under control).

Use a laser level or a hose water level to compare the boiler's water line to the wet return piping at the far end of the main.

IMO the European smart valves may have helped solve a comfort issue but caused or enhanced system issues.

KarlW

@109A_5

You are exactly right on the valves, and I have since resolved the near-constant calling for heat by changing the mode.

The valves themselves only call for heat sometimes. Here are the calls for heat in my benchmark cold room, my glass-enclosed 2nd-floor sleeping porch - which has more heat loss than a typical room in my 1920 minimally-insulated house - between 25% and 50% - right in line with your example numbers:



Here's the same chart for the thermostat: You can see below where, on Thursday, I changed the operating from radiators being able to turn the boiler on to just the Thermostat being able to turn the boiler on. The real culprit for the constant run time was that valves would call for heat at different times, and so as one was done heating, another was freshly calling. Changing the operating mode fixes that.



This is all related to the classic problem of the thermostat not being in a cold room of the house. For years, I've been battling with the manual valve in my thermostat room to throttle the radiator just right to match my colder rooms since before I installed the valves.

But changing the thermostat mode came at a comfort price - my mother-in-law is staying on the third floor, and it hasn't been able to keep up since I changed it on Thursday:



Part of the problem is the radiator taking longer to heat up from cold (45 mins from vs. 20-30 mins for others), and part of it is from the weird placement of the radiator and valve in the room (an interior corner). I am purchasing the reflective radiation sheet from Home Depot this morning, which has worked wonders on other radiators.

I am not opening my walls to figure out a piping problem. The cost-benefit isn't there for one radiator that almost works.

The water hammer is clearly related to the slope and consequent height of my wet return and the installers who replaced them two years ago. I have a 10-inch drop over around 36 feet, slightly more than a 2.5% drop. This puts the high end of the wet return (14.5 inches) only 12 inches below the main waterline (+/- 26 inches).

I can now reproduce this water hammer on demand - by lowering my boiler water level by 2-4 inches (still above the low water cutoff), I get steam entering the wet return at the vertical drop of the wet return (the high point). Water hammer occurs when the radiator thermostatic traps open and try to drop water from the wet return to the dry return. I have confirmed this with an IR camera and would post it if FLUKE didn't use a proprietary image format - you can see the tee where the steam drops heat to >90º C when the water is low but hovers at about 50º-60º C when the water level is higher.

I plan on lowering the pipe another 8 inches, but I'd still have a 2.5-inch slope over the 36 feet or a 0.5% slope. This will give me another 4 ounces of pressure and should have the benefit of reducing the boiler pressure cycle times as well.

KarlW

Update with IR Photos! (Older FLUKE Ti25)

The first photo (taken at the end) is of my header filled with steam for calibration, 205º F, right about where it should be:



The next few photos are of the steam main drop at the wet return, about 18" from the farthest and highest point in the system (the dry return drop). This point is about 14 inches off the floor and 10 inches below the waterline. (This is the "B" dimension if I'm not mistaken).

This point is immediately below this picture from above:


The first picture is just after I lowered the water to the near minimum the boiler will run without activating the low water cutoff and refill (this happened to me as I was setting it up). As the boiler had been doing its thing on this average to slightly warm January day, this is close to "normal" operation. At 120º it looks like an acceptable temperature and is almost certainly all water:


The next picture is 8 minutes later, after three or so boiler cycles (I am short cycling, but I likely have to deal with it). This is where I am getting significant water hammer. At 183º, I almost certainly have some steam mixed, causing the water hammer as my radiator traps open and drop the water in - you can hear the water flow down the dry return instantly before the water hammer.


The steam main does cool quickly between cycles, as this is two minutes later, about the time the boiler has depressurized and the pressuretrol kicks the boiler back on:


Yet 90 seconds later after another heat cycle, the steam is back:


At this point, I refilled my boiler higher and let it continue to run. Sixteen minutes later, my wet return has cooled down quite a bit, and the water hammer is gone (also has the best background showing the wet and dry returns). Close observers will note this picture was taken 30 seconds before I took the header picture I posted first.


In 2021/2022, my wet return developed a leak and rusted through. Exactly two years ago this week, I had my entire wet return replaced along with some dry return that developed a leak (I assume to water hammer from a failed trap). However, as I mentioned above, they added a lot of slope to the wet return, treating it as a condensate line. This picture from under the slop sink adjacent to the main drops clearly shows how high they raised the wet return. That's not a shadow! That's the location of the original wet return:


So now I have to deal with the contractor - and you can read above where I've complained about the expertise in Western NY. That said, although the expertise was lacking, the workmanship is excellent, and they put pipe supports like the one here every 10 feet, and it looks good. This was a quality repair that can be compared with any out there. It's a shame they didn't know it was a WET RETURN, NOT A CONDENSATE line.

The contractor is coming over tomorrow I am going to make the case that they fix this under warranty. I'm not asking them to replace the 60 feet of pipe they installed but to lower the pipe and replace the three vertical pieces to the tee as needed. Although flattening the pipe will move the tees a little, it's black iron pipe, and I'm sure they can muscle the pipe the inch or so they'd need to line back up to the tees. It should take at most 10-15 feet of pipe in three sections - and they can likely reuse some of the existing 2-year-old pipe.

Is this an unreasonable ask of the contractor?

mattmia2

In order for the steam to get in to those risers the pressure has already pushed the air out. if the water seal was working right the steam would stay near the top and most of the riser would be cooler. you can get some water hammer where the steam just contacts the water at the bottom of the riser.

You don't have to re-pitch that whole pipe, you can just bring it down like this

KarlW

@mattmia2 I see what you are saying and agree, but that’s a horizontal bend to avoid a drain, not a vertical bend. Also, if it is above the water line, I’d worry that I’d be creating an air trap later due to who knows what. 

As there are no vertical bends in the pipes, lowering the whole thing en mass from the boiler room is likely the easiest way to do it, but I’ll be open to suggestions!

109A_5

Hello @KarlW,
If you are going to open up the system, you probably should put in a valve to drain / flush the wet return out.

KarlW

Closing this out: they finally came and lowered the pipe yesterday - I was relaxed on the contractor's schedule as I had a clunky workaround and we got the cold snap so I didn't mind them helping folks who had emergency issues.

It's slightly higher than the original, but not by much and I'm fine with the level, I now have a very light slope. As with the original replacement, the workmanship in impeccable (a rare Unionized residential company).

Here's the pics, don't worry, they put in a new pipe!





My wife reported the first afternoon/evening of no banging she can remember, I'm not quite as optimistic, but we will see.

@109A_5 I actually do have a wet return drain/flush (it may be in one of my boiler room pics), and they used it to empty the return before doing the work pictured.

@ethicalpaul in another thread you doubted the original pipes were 102 years old. If you saw how the gumwood molding was created into a box and doweled into my foundation wall, you wouldn't doubt it that it was original.