Expansion Tank Placement on Closed Loop System in Relation to Circulator Pump

gabepage03

Hello everyone, I’ve started to do a lot of research on this topic and I keep coming back to the same problem. I have a closed loop hot water system and I want to replace my old metal expansion tank. Problem is - the expansion tank is piped in AFTER the circulator pump and boiler. So, the circulator pump is placed at the closest point of return BEFORE the boiler while the expansion tank is piped at the first point of supply AFTER the boiler returning water to the system. I have read that you always want the circulator pumping away from the expansion tank. Am I alright to place my new 14 gallon Extrol tank where the old one was? I realize that I may have the supply/return terminology mixed up nevertheless the point is that my circ pump is pumping into the boiler and then exits toward the expansion tank. I’ve attached some pictures with directional flow arrows to display exactly what my system looks like. Please help!

hot_rod

Ideally the expansion tank connection would be on the inlet side of the circulator. You have a union and a reducing coupling on that return piping, it would be fairly easy to add a tee where the reducing coupling is to connect the new diaphragm tank there, also the fill valve.

You also need to add an air purger on the supply out of the boiler with a diaphragm style tank.

You are getting into a bit of work, requiring cutting and threading some of that large steel pipe.

gabepage03

@hot_rod I already re-piped a small section of 1/2” pipe near my fill valve. I replaced the PRV fill valve and also added a back flow preventer. It wouldn’t be hard to add the expansion tank right after my fill valve in the area where I just recently did some work. This is most likely what I will do. Then I will just plug off the hole where the expansion tank used to be piped in. Does this sound like a suitable solution as far as the expansion tank goes?

gabepage03

@hot_rod Another question for you regarding the air scoop. I just found this air vent from watts. Could I just thread this into the location where my old expansion tank was piped in? This would make for a very convenient solution that would not require any cutting/threading. 

hot_rod

That is a float type air vent. It is intended to go into a high spot in the piping, at the top of risers or in a scoop type air purger. Just drilling it into a horizontal pipe will not do much.

The very best are the microbubble type purgers. They use a media inside to stop and collect all air, bubbles, entrained air, everything.

For the tank to pump relationship, you could move the tank down by the pump, or if it is easier move the pump up on the supply, add the purger and tank there.

On a cast iron, low pressure drop boiler the tank can always be on the return, the pump could be there or on the supply.

The air purger needs to be on the supply, at the hottest point in the system.

Here is a pic of the dynamics in play when pumping away from the tank. The pump pressure adds to the fill pressure.,

mattmia2

You could replace the sections you rework with reducers and much smaller copper pipe.

Is there a problem with the compression tank?

HomerJSmith

Is that a converted steam sys? Just wondering.

There are several ways to putting in a new bladder tank. One can use an Amtrol Fill-trol or Extrol Ex-tank. The size of the tank depends upon the volume of water in the sys and the temperature of the water. There are sizing calculators eg. https://www.supplyhouse.com/sh/control/ExpansionTankSizeCalculator?intcmp=calc;extrol-prod

A Fill-trol tank has a fill valve on it and sets the boiler water pressure to the air charge on the tank, eliminating a separate pressure fill valve. A Extrol tank needs a separate pressure fill valve to regulate the water pressure in the sys, and the bladder air pressure in the tank need to match the setting of the pressure fill valve.

The main thing is to get a tank that is sized to an acceptance volume that satisfies your sys's needs.

A cast iron boiler has little pressure loss thru the boiler heat exchanger and when the pump is located on the input to the boiler and the Ex-tank is located on the output of the boiler, you are essentially pumping into the Ex-tank, a no no. Funny things happen in a sys when you do that.

A Caleffi dirt mag (because you have a lot of iron in your sys) with an air vent, a combination dirt mag and discal on the output of the boiler is needed. You want the air eliminator on the hottest water to remove the oxy in the sys, and that is the output of the boiler. You want, as stated in this post, the Ex-tank on the input to the pump at least 10 pipe sizes before the pump flange to mitigate turbulence in the pump.

gabepage03

@HomerJSmith @mattmia2 @hot_rod Alright so I figured I would respond to everyone at once with more pictures. I appreciate this immensely and I can tell that you fellas have a great deal of knowledge in this. So yes, it was previously a steam system and was converted to water. I have cast iron radiators throughout my house with bleed valves on them. No, there is not a major problem with the current tank besides the fact that it is very old. The bleed valve did bust off of it but I could probably get it back on. As you can see I’ve done some work already and replaced an old section of the feed line that was clogged with sediment. I replaced the main valve, the fill valve, and added a back flow preventer. I currently have the system drained so I figured I would do as much maintenance as possible. The pump needs to be replaced badly and I’ve got a direct replacement that fits perfectly. I want to note that I do not plan on manipulating any of the large piping in the system. With all of that said, I have the following questions:

Should I even bother installing a new tank?
If I should, what would be the best course of action be?
Does it absolutely have to be on the suction side of the pump considering it was running fine in the past?
How necessary is the air separator considering there was never one in the past?

I appreciate your help greatly.

EBEBRATT-Ed

@gabepage03

It is always better to pump away from the expansion tank if possible.

However, there are literally thousands of jobs piped like yours and they worked for the last 80 years or so.

If it worked with your old tank it will work with your new tank, especially with an older system with low resistance

gabepage03

@EBEBRATT-Ed Is there a difference with the way new tanks are designed as opposed to the old metal one that would somehow throw everything out of wack?

mattmia2

That looks like it was a gravity hot water system, not steam.

The compression tank has air and water in the tank. The system should be designed to move any air in the system to the tank. If you remove the compression tank and replace it with a diaphragm tank you will have to remove the air instead of moving it to the tank. A modern circulator would use a lot less power but you would have to be a lot more careful about removing iron particles from the system with a wet rotor circulator because the magnet in it would attract the particles.

Since it is a converted gravity system the piping is a lot larger than it needs to be. The water content of the system is also large so you need to account for that when sizing a replacement expansion tank.

gabepage03

mattmia2 said:

That looks like it was a gravity hot water system, not steam. The compression tank has air and water in the tank. The system should be designed to move any air in the system to the tank. If you remove the compression tank and replace it with a diaphragm tank you will have to remove the air instead of moving it to the tank. A modern circulator would use a lot less power but you would have to be a lot more careful about removing iron particles from the system with a wet rotor circulator because the magnet in it would attract the particles. Since it is a converted gravity system the piping is a lot larger than it needs to be. The water content of the system is also large so you need to account for that when sizing a replacement expansion tank.

Would you recommend that I replace my tank with a another compression tank instead of a diaphragm tank? If that’s even possible…

hot_rod

Is it in a location where it will do damage if it leaks?  Usually a drip, not a rupture when they fail. You could let it run until it fails.

gabepage03

hot_rod said:

Is it in a location where it will do damage if it leaks?  Usually a drip, not a rupture when they fail. You could let it run until it fails.

No it won’t be any damage to anything if it leaks. I just wanted to replace it since I have the system drained out. I don’t plan on draining the boiler system again in the period that I will occupy this home. That is why I wanted to do as much preventative maintenance as possible on the system. Since it’s mid summer I have plenty of time to get the job done.

gabepage03

@hot_rod Is there a tank on the market that would be suitable as a direct replacement for my situation?

hot_rod

I’ve never seen a vertical tank like that with the sight glass on the side. Plain steel tanks are still available, Wessex, , Taco, B&G for example.

A diaphragm tank would be about 1/3 that size, but you would need to add an air separator. More piping work involved also

psb75

That is a nice looking cellar. The tank and stand appear to be mfg.d shortly after the demise of Monroe, MI 's famous citizen-son Gen. G.A. Custer.

gabepage03

@hot_rod After everyone’s advice, I’ve decided that I will just keep my old tank and just replace all of the old 3/4” galvanized piping with copper that connects the tank to the system. I will post an update when I eventually refill my system and hopefully get everything working. I really appreciate your advice @hot_rod in particular. You’ve been a major help and I probably would’ve done some things wrong had I not posted on here.

gabepage03

I also have to replace this leaking radiator valve in my 3rd story attic so wish me luck on that! As you can see, I do have an air separator on this radiator which is at the very top of the system. I wonder if this is sufficient for air separation for the entire system?

gabepage03

FYI, I do electrical work for a living and that knob and tube is disconnected

EBEBRATT-Ed

That's good. I was just about to mention the K & T

mattmia2

Where is the valve leaking? Do you need to replace it or just repack it? Be careful with repacking, the packing is frequently asbestos.

hot_rod

If you have enough air vents on radiators, that may be enough to keep the system air free. It will take some time after a drain and refill to get all that piping and radiators air free

gabepage03

mattmia2 said:

Where is the valve leaking? Do you need to replace it or just repack it? Be careful with repacking, the packing is frequently asbestos.

The valve is leaking from the base of the stem. I suppose it could be re packed. However I know nothing about that process.

gabepage03

I would also like to mention that I am not the genius who wrapped it up with electrical tape at an attempt to stop the leak.

gabepage03

hot_rod said:

If you have enough air vents on radiators, that may be enough to keep the system air free. It will take some time after a drain and refill to get all that piping and radiators air free

All of the radiators have bleed valves but they are small manual bleeds not like the one pictured on my attic radiator. Is the device on the radiator above an "automatic" bleed valve?

mattmia2

That is an automatic air vent on the radiator in the attic. Will that become occupied space? I would be very careful with
1. The automatic air vent leaking and going unnoticed.
2. the radiator becoming air bound or otherwise something happening to it that it doesn't heat and then freezing.

If the valve is leaking from the stem it is likely the packing, You can replace it with teflon string packing or even just add a little and tighten down the nut if it isn't in bad shape. Sometimes just tightening the nut will do it too. If you go with the string packing, add some, tighten it down, remove the nut, add some more, don't try to add it all at once, if you crank on the nut hard you can break it. Clean up the stem with some scotchbrite if it isn't smooth.

gabepage03

mattmia2 said:

That is an automatic air vent on the radiator in the attic. Will that become occupied space? I would be very careful with
1. The automatic air vent leaking and going unnoticed.
2. the radiator becoming air bound or otherwise something happening to it that it doesn't heat and then freezing.

If the valve is leaking from the stem it is likely the packing, You can replace it with teflon string packing or even just add a little and tighten down the nut if it isn't in bad shape. Sometimes just tightening the nut will do it too. If you go with the string packing, add some, tighten it down, remove the nut, add some more, don't try to add it all at once, if you crank on the nut hard you can break it. Clean up the stem with some scotchbrite if it isn't smooth.

Yes, Eventually I would like to make the attic into a livable space. I will replace the automatic air vent and keep an eye on it. When the system was running just a few months ago in the spring the radiator was heating even with the leak in the valve. I kept it cracked open as much as I could without causing too much leakage. I just watched a video of someone using teflon string to repack a valve. Doesn't look too difficult. I will give it a try. Thanks.

mattmia2

The system is under essentially the same pressure from the supply and return, it will leak even if the valve is closed. Moving the stem in to different positions may make it leak more or less.

For the automatic air vent, you can just tighten the cap on it then it will be sealed. Won't vent air but also won't leak. Then you can open it if you need to vent air out.

hot_rod

you have what is known as an "air management" hydronic system with that type of expansion tank.

You need to manage, or maintain that air bubble at the top of the tank for expansion space.
So you do not want to add an automatic air purger at the boiler, else it will remove that air bubble over time.

IF you change to a bladder or diaphragm some day, the air bubble is trapped in the tank, so you can add an auto air purger at the boiler.

You want the radiators to fill with water, so an air vent up on top allows that air to come out. There are manual vents, automatic vents and combination vents.

Manual vents have a thumb wheel, screw slot or square skate key mechanism to open them.

Float type air vents shut off the bleeder when air comes out water fills and the float rises.

Combo type use cellulose fiber washers as the shutoff function. When air is present the discs are dry, air comes out. As soon as water hits them the discs swell and shut off. They tend to work better on dirty, rusty old systems as there is no needle valve to get debris stuck in. Turnn the know the opposite way and it is a manual bleeder valve. The small chrome valve in the pic.

If you use float type vents, add a service check show on the left. It allows the vent to be removed for cleaning or replacing.

On those float auto vents Caleffi has a safety cap that can be added. It adds those fiber washers as a second protection. The small brass cap shown, called a hydroscopic safety cap. These are ideal when you have a vent in a space where a leak could damage the ceiling, floor, walls, etc. The hydroscopic caps should be replaced every 3 years or so.

Additionally you can put a metric to NPT adapter on the vent and put a discharge tube down to a safe place, lower right fitting.

Just know any device with a small port or opening is prone to sticking with dirty rusty, chunky water commonly found in old systems like yours. So any air vent that functions from time to time will need cleaning or replacement, plan accordingly.

HomerJSmith

Holy Cow, you got tube and knob wiring? I hope it's abandoned. The house was built in the '30's?

gabepage03

hot_rod said:

you have what is known as an "air management" hydronic system with that type of expansion tank.

You need to manage, or maintain that air bubble at the top of the tank for expansion space.
So you do not want to add an automatic air purger at the boiler, else it will remove that air bubble over time.

IF you change to a bladder or diaphragm some day, the air bubble is trapped in the tank, so you can add an auto air purger at the boiler.

You want the radiators to fill with water, so an air vent up on top allows that air to come out. There are manual vents, automatic vents and combination vents.

Manual vents have a thumb wheel, screw slot or square skate key mechanism to open them.

Float type air vents shut off the bleeder when air comes out water fills and the float rises.

Combo type use cellulose fiber washers as the shutoff function. When air is present the discs are dry, air comes out. As soon as water hits them the discs swell and shut off. They tend to work better on dirty, rusty old systems as there is no needle valve to get debris stuck in. Turnn the know the opposite way and it is a manual bleeder valve. The small chrome valve in the pic.

If you use float type vents, add a service check show on the left. It allows the vent to be removed for cleaning or replacing.

On those float auto vents Caleffi has a safety cap that can be added. It adds those fiber washers as a second protection. The small brass cap shown, called a hydroscopic safety cap. These are ideal when you have a vent in a space where a leak could damage the ceiling, floor, walls, etc. The hydroscopic caps should be replaced every 3 years or so.

Additionally you can put a metric to NPT adapter on the vent and put a discharge tube down to a safe place, lower right fitting.

Just know any device with a small port or opening is prone to sticking with dirty rusty, chunky water commonly found in old systems like yours. So any air vent that functions from time to time will need cleaning or replacement, plan accordingly.

Excellent information! I appreciate this.

gabepage03

HomerJSmith said:

Holy Cow, you got tube and knob wiring? I hope it's abandoned. The house was built in the '30's?

I do not have active knob and tube in my home. My house was built in 1928. Orignally had knob and tube then was upgraded to "BX" armored cable. Currently, most of the house is modern Romex.

gabepage03

Just wanted to update everyone that helped me out on this. I have my system filled and up and running. I ended up replacing the old metal compression tank with an Extrol Amtrol SX-40. I spoke with a number of people who told me that this tank will be suitable for my system. So far no issues! System is sitting cold at a perfect 15 PSI and 18 when it’s hot. I also got my new circulator pump in and changed out various valves and air vents. I appreciate everyones help! 

leonz

I am sorry to see that you changed that tank.
A higher water volume with a greater trapped air volume in a steel compression tank keeps the circulator impeller full of water.

The failing automatic air bleeders, crawling around on my knees and poor system pressure while hot are the reason why I eliminated them from my heating system.

To replace the valve stem packing you need a combination packing pick and hook tool and the correct size stem packing. It would be easier to just replace the entire valve. JUST BE SURE to bring the valve
with you when you go to the plumbing supply warehouse to give it to the counter clerk to make sure they give you an identical valve to replace it.

As far as replacing the bleeder vents on the radiators you can use 1/4" ball valves, short nipples and
elbows and have leak free valves. A short nipple on the ball valve can spill into a small pail or coffee can when bleeding them.

gabepage03

@leonz I was told by multiple techs that this was a good tank replacement. I only have 1 air separator on the very top radiator in my house. I have already repaired the leaking valve stem with some new packing. I replaced all of my bleed valves on the radiators as well.

hot_rod

Are you sure about this Leon??

I am sorry to see that you changed that tank.
A higher water volume with a greater trapped air volume in a steel compression tank keeps the circulator impeller full of water.


Pros and cons on compression tanks, 60- 80% of the tank capacity on first fill will be water to squeeze the air space to fill pressure. So right off the bat you add more water to your system, which then needs to be accounted for in the tank size for adequate expansion. Could be as much water in the tank as in the system. With a diaphragm tank, properly pre-charged you add no water at fill, the diaphragm will be against the nipple until expansion starts..

Since the air and water are sealed from one another the hydro-pneumatic tanks will be 1/2- 1/3 smaller or more.

You need to properly support a compression tank that could fill with water.

And you need two tall dudes to easily install them, according to this old Extrol ad

Noon CST tomorrow we have Coffee with Caleffi, talking expansion tanks, close to 700 sign ups right now, thanks all!