Old gravity system w/standing cast iron rads

Brad White_52

The obvious question, are you pumping away from the expansion tank? Can you post a diagram?

Thinking the usual pumping to the ET and sucking in air. But what is the system pressure? Height/2.31 = PSIG plus 4 PSIG for the top. That would be your cold fill pressure.

Also the Grundfoss 26-96 might be a tad high in head. Assuming you are moving about a 20 degree Delta-T (18 GPM say) you would have about 10 feet of head. May be ok given the Munchkin pressure drop but the system side probably has less than four feet of PD; you may be over-pumping there. Might it be a VS model? Give you some wiggle room.

EDIT: I have read that the Munchkin requires P/S piping but is that really the case? Thinking that you could handle both the Munchkin PD and the minimal system PD in one bite.

Just some thoughts.

Heatman_2

Old gravity system w/standing cast iron rads

This winter I installed a Munckin 199M in a 90+ years old 3 story home. All original gravity piping and cast iron rads still installed. There is only a office and a bath on the 3rd floor with one radiatior each. About every 2 weeks these radiators will stop heating and air will have to be removed for them to come back online with the rest of the system.While I was changing out the boiler, I added TRV's to the 2nd floor rads and these two as well. These are the only changes I made to the heating system, besides near boiler piping. I tried a Hoffman 508# automatic vent steam/water, it automatically purged air upon startup, but now a week later I've got air again. I'm using a grundfos up 26-96 for my central pump , and another 26-96 for the boiler pump. Any ideas??.... Oh also, its new owners who hired me to do the work, so I don't know if these rads had problems before me or not?.

Heatman_2

My expansion tank ties in with the cold water fill, and that is too a nipple that was tapped into high on the return piping. I've got a spirovent on the suction side of the circulator, but I plugged the bottom tapping since I was reuseing the old location of exp. tank and cold water fill. Does this sound like my problem?

Mike T., Swampeast MO

That 26-96 seems to be an inappropriate choice for the radiation as it's high-volume, high-head. Don't forget that those big gravity pipes mean zero head loss. At the flow rate needed through a given radiator of a typical gravity system the TRVs offer very little head as well. With your "mixed" system with TRVd and non-TRVd rads you still need a high-volume, low-head circulator like a Taco 007 or B&G 100.

If still using the plain expansion tank near the boiler, install a B&G Air-Trol fitting on the tank!!! If you still have the plain tank I bet it's now waterlogged--either that or you have a leak in the system.

Brad White_52

So long as the circulator is downstream

of the expansion tank connection (and relatively close to it) that should be OK. If it is pumping TO the expansion tank I would submit that it is the source of your issues.

(I am not entirely clear on the relationship between the ET connection point and the circulator. You said return side but could mean on the boiler or otherwise. Just checking.)

If you want to be sure, tie in the expansion tank to the Spirovent tapping.

While you are at this, you may also want to add several tanks, maybe three, for the volume of the gravity HW piping and radiators. Characteristically, one #30 tank is never enough. Two might, but three will work in all cases I have tried in single family houses. Less $ than a large #60 overall and you have redundancy. Manifold the tanks together and connect to the Spirovent bottom tapping.

Brad White_52

Well, not \"zero\" head loss

Otherwise you would have no flow! (Playing with you, Mike!)

But your point is clear, the PD is piddling indeed and it is a lot of pump. If 18 gpm (my assumption only), a 25-64 might make better performance at about 3 feet of head. A VS model of the same even better.

A Super Brute on speed 3 may make the grade for a slightly higher delta-T.

Heatman_2

I piped the system just like the munchkin diagram showed, p/s method. I replaced the expansion tank w/ 2 60's( They are bigger than 30's) extrol tanks. I re-used the tap in location on the system piping return header, right before it drops down into the p/s t's. Do you guys think I should cap this nipple and use the tapping in the bottom of the spirovent, this would be right next to the boiler pump.

The system circulator was replaced a year previous to the new owners buying the house, so I re-used it(Distributor said it would work). When calculating head for a system like this one, do I just figure the longest run with the rest of the components in the piping (flow checks, spirovent, ect). Sounds like I might have a couple of small things causing this nuisance on the 3rd floor.

Heatman_2

If you have a pump on the return of a boiler and an expansion tank right on the supply outlet of the boiler is that still considered pumping toward the exp tank

Steamhead (in transit)

Heatman, how much radiation

is on that system? Meaning the amount of square feet EDR, not the building's heat loss.

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Dave_12

Heatman

Yes, this is pumping toward the point of no pressure change. Your pump should be pumping away from the expansion tank and point of tie in for the make-up water.

Heatman_2

I'll have to check and see if I kept my notes in that job folder. I did a radiation count and used E.D.R. book with and average water temp of 170. Most of the rads are the Peerless Four-Column by American Radiator Co. (1916). I was able to TRV the whole 2nd Fl and 3rd Fl but the rads on the main level all had 1 1/2 piping and larger.I'm pretty sure I saved my notes.

Jerry_15

If your expansion tank ties into the fill valve it is probably an extrol and the pressure in the system is controled by the TANK PRESSURE. Only the special extrol expansion tank, with the special tit on the end, will operate this valve. Jack the tank pressure up to 20 PSI (if it's the right one), and call me in the morning.

Jerry_15

I agree, a 96 is over the top, but I don't think that's your problem. Stick a test pressure gauge on the boiler drain, you might be in for a surprise. Check my other note up top about the tank and fill valve. Good luck.

Heatman_2

I don't understand what your saying about the tank pressure. I understand they are pre-charged with air, but I thought my system pressure was determined by how much water I fill the system with and where my pressure reducing valve is set, please set me straight, thanks for the patience with the newbie.

Jerry_15

Most fill valves can be adjusted at the valve, but there is one brand that that has the tank attached to it that is adjusted by the tank pressure itself, AND ONLY THE SPECIAL TANK MADE FOR THAT BRAND WILL ACTIVATE IT - CHECK YOUR SYSTEM PRESSURE WITH A TEST GAUGE SCREWED ONTO THE BOILER DRAIN AND RUN IT UP TO 20 PSI. IF YOU CAN. Good luck.

Randy_23

spirovent

You said you have a spirovent on the suction side of the circulator. Do you think your sucking air in each time the circulator starts? I would cap the spirovent and see what happens.~Randy

clammy

gravity

I,ve been watching and reading your post .Now i was always under the impression that when converting a gravity to pumped that you really don,t need alot of pump head becuse of the size of the piping i have always gotten away with a b&g series 100 and as of lately have used taco oo7 with good results .As usuall i put my system pump with my sprionvent and expansion tank and water feed on it's suction side of the system pump and my boiler suppy and retuurn also .Could the trv that you installed have thrown the system out of balance by adding a little more resistance to your piping just a question .Here's a short of a munchkin 80 on a old gravity with honeywell unique valves ,this system worked like a chram have not had one promblem .Peace and good luck clammy

JK_3

The tank that he is referint to is called a filltrol tank and dors control the system pressure . It is very possible that this is your problem in that as your water contracts there is not enough pressure to keep the system full of water. The only way to increase the pressure on this type is to add air to the air fitting on the tank whilr there is zero pressure on the tank and chech with a tire guage. Ihope this helps.

JK_3

I also need to mention that the filltrol tank needs to be connected with a filltrol valve. This valve will be brass and show imprints indicating tank,system,and supply(inlet)

Heatman_2

I've used two extrol tanks on this install. I looked in my Johnstone book and I see the fill-trol your talking about, it says it comes with the reducing valve that you need. I don't understand the difference between the two systems. Is the filltrol the better choice in the kind of app. I'm in.

JK_3

I Prefer to not use the filltrol because of the way you have to raise the pressure as well as the fact that there is no fastfill for temporary raise of the pressure. If you have the filltrol tank you must use the filltrol valve as someone else said or else it wont acctuate properly. Also if your fresh water onnection is through a filltrol valve then an extrol tank will not work.

Heatman_2

I have two extrols manifolded with a B&G B-38 pressure reducing valve. I have this and system pressure set about 19-20 psi. This connection is far away from either circulating pump, but with my central heating pump on the supply and these connections are on my return header before it drops drops down to the boiler, Is that still considered pumping toward the exp. tank.

JK_3

Your problem could be a couple of things. First are you sure that the guage that you're reading pressure from is accurate (mabye not enough pressure)or mabye the expansion tanks are not large enough(there is a formula for sizing expansion tanks). If you need that formula I could get it for you when I get to my other office or I beleive it's in dan's book called "How come". Also how close is the tanks to the suction side of your pump. I would suggest using the tapping on the spirovent by manifolding your tanks there.

Gary_17

tank pressure

If you adjust the system presure up, don't forget to adjust the tank pressure to match it.

Heatman_2

Is a small air compressor used, or does somebody make a tool w/gage built in to adjust pressure?

Gary_17

adjusting pressure

I just use a small compressor. Make sure the system press. is 0 before you adjust tank press. My comp. plugs into my truck lighter, so I have to remove tank and plug the opening to take it out to my truck. Someday I'm going to get a little 120V one.

JK_3

To be safe I use a bike pump and tire guage(don't want to blow out the diaphram)

JK_3

I have that formula if you need it(sizing expansion tanks)

Heatman_2

That would be helpful

JK_3

If you replaced a steel tank it would be helpfull to know the size of the tank even if you could just measure it and we can figure out the volume. If not then you need to figure the square foot of radiation.

Jerry_15

I thought you said before that the ex tank was connected to the fill valve, which led me to believe it might be the filltrol. Looks like I was right. I never use them either, but the b& g is all you need. If you have filltrolls as well cut that mess out of there and just put in a tee for the right size tank NOT THE EXTROL TANK WITH THE METAL TAB COMING OUT OF THE END. I don't they will work without their specialvalve to attach to, and vica versa A single #30 tank will generally fill the bill on any single family residence in my experience. Put a valve on the tank, pressure the tank and system to 15` psi and fire it up. If you get a pressure rise over 5 psi, put it back on the truck for the next job and put in the next size tank (after checking pressure first), you don't even have to turn off the boiler cause you have a shut off valve! Let's see 2 minutes to change the tank, calculating the water volumn in an old system. Tough call