Taco pressure reducing valve leaking - questions about copper to cast iron connection

[mcat]

Hi all,

I'd like some insight here as I have been going back and forth with the local municipality to shut the water off so I could at least sweat the old gate valves off in order to do a repair on a slow leaking pressure reducing valve but they are claiming this is not an emergency and may get to it early next spring.

This morning I woke up to a wet basement due to what I assume is an original pressure reducing valve and back flow valve combination that has begun failing. The drip from the valve is constant ( I realize there should be a copper tube running closer to the ground but the home inspector never mentioned this I just found out about this from research )

I have a Taco 334-T3 pressure reducing valve I ordered previously but it just dawned on me that the outlet is a threaded cast iron body and I would need to use a 1/2" threaded copper end to affix to it, and that will undoubtedly cause corrosion and leak again. The original Taco valve is brass but I can't find a suitable replacement for what I have, there are no markings or numbers to go on.

I've attached pictures ( named accordingly ) of the previous valve and it's install ( not done by me it came with the house when I purchased it ) and the new valve I have and the connector in question to use to get it installed. The gate valve mounted right next to the valve is pressed up to the floor joist and I haven't been able to see if it would even turn but it's too close to the valve I believe to put a wrench on without breaking something.

I came across this Taco t3 64 model but it looks completely different from the one I have currently but it has a brass body and not cast iron and is shorter.

Ideally I'd like to run what I have on hand but the connection from copper and cast iron has me concerned I'l run into leaks or corrosion in a few years from now.

Any insight would be greatly appreciated. I'm tempted to wrap the threaded copper connector in pro dope to help avoid corrosion and tighten it down into the valve after I've sweated a piece of it onto some 1/2 pipe and use a coupler to put it into the existing line.

 

[Reach4]

I'd like some insight here as I have been going back and forth with the local municipality to shut the water off so I could at least sweat the old gate valves off in order to do a repair on a slow leaking pressure reducing valve but they are claiming this is not an emergency and may get to it early next spring.

Many do it themselves. One name for the common tool is "curb key".

Compression and SharkBite can go onto copper pipes while they still have residual water.

You might be able to keep the existing gate valve in place to let it slow the flow enough to put a new ball valve after the gate valve.

 

[Sponsor]

 

[mcat]

Many do it themselves. One name for the common tool is "curb key".

Compression and SharkBite can go onto copper pipes while they still have residual water.

You might be able to keep the existing gate valve in place to let it slow the flow enough to put a new ball valve after the gate valve.

I have a curb key but was now told explicitly by the municipality to not touch the valve or face hefty fines and be liable for any damage. ( Ironic since I'm the one who's been waiting for over a year to get this sorted ) They buried the valve in dirt for 50+ years and just recently marked where it is but said they need a crew to come out and evaluate and maybe to see if it even shuts off.

Right now I'm thinking to close the gate valve in the basement where the main line feeds up which is after a initial gate valve that is extremely corroded and bleed the system and see how things fare from there. There's a city water meter sandwiched between two gate valves.

My other concern is the connector to the new cast iron Taco valve I got, I only have a copper 1/2 MPT threaded adapter and I'm not sure if coating the copper connector in pro dope will be enough to prevent any corrosion from dissimilar metals.

Added a pic to further illustrate the line from the street to the basement.

 

[mcat]

I've also got some ball valves 1/2 " and 3/4" and have always used propane for plumbing work. Is there any benefit to using map gas for sweating on ball valves or is the old method of wrapping them in a wet rag with the valve open ( per the manufacturer instruction ) good enough and keep the flame pointed away from the valve body?

 

[Reach4]

My other concern is the connector to the new cast iron Taco valve I got, I only have a copper 1/2 MPT threaded adapter and I'm not sure if coating the copper connector in pro dope will be enough to prevent any corrosion from dissimilar metals.

I am confident that pipe dope and/or tape will not serve as an electrical insulator. I don't know if there is a dissimilar metals problem.

It seems to me, from what I read, that the corrosion problems with cast iron are increased by replacing water with fresh (still-oxygenated) water.

 

[mcat]

I am confident that pipe dope and/or tape will not serve as an electrical insulator. I don't know if there is a dissimilar metals problem.

It seems to me, from what I read, that the corrosion problems with cast iron are increased by replacing water with fresh (still-oxygenated) water.

That's interesting, the water supply line is from a city municipality not a well. I got confused further when I looked at my boiler and see all sorts of female 3/4 copper fittings threaded into cast iron male ends for water as well. Perhaps I'm overthinking this and this metal issue is reserved for hot water boilers that are electric ( mine is gas ) for drinking water opposed to forced hot water heating systems?

I did search around prior via google for "pressure reducing valve has female cast iron fitting, can I thread a 1/2 in copper mpt with teflon tape?" resulted in responses saying that:"Yes, you can thread a 1/2 inch copper MPT fitting into a female cast iron fitting with Teflon tape, but you should use pipe dope for a better, more permanent seal and to prevent potential damage. While Teflon tape can work as a lubricant, it is not a true sealant and may not hold up over time as well as pipe dope, especially with dissimilar metals like copper and iron, which can cause galvanic corrosion over time."

I managed to get the main top gate valve shut and drained the system and tried the gate valve right before the original Taco pressure reducing and check valve assembly. It wouldn't budge at all so I left it alone for the time being.

I went over to a local home depot after and asked around but nobody I spoke with had any idea of what galvanic corrosion was or even if they sold dielectric union's, the only thing I could find was for hot water heaters but the fittings were wrong.

I did find this link below but it's 4 days out from shipping and no local store has anything. So odd that something that is said to be needed in a situation like this isn't available at any store near me and I even tried online via AMZ.

PLUMBFLEX PLUMBFLEX 1/2 in. Male x Sweat Dielectric Union Zinc Coated Steel x Brass Union Fitting 12H-DUMS - The Home Depot

Add perfection to your job with the use of this The Plumber s Choice Male x Sweat Dielectric Union Zinc Coated Steel x Brass Union Fitting. caps.

www.homedepot.com

I'm wondering now if due to the closed-loop hydronic nature of the system and the mention of fresh still oxygenated water being the culprit, with any water entering in is quickly de-oxigenated, therefore resulting in the need for any dielectric union moot? I may be alright in this instance.

 

[Fitter30]

Map gas is hotter than lp by 130° f . Works best with a turbo torch. If the regulator is 3/4" fpt can use 3/4" mpt X 3/4" sweat dialectic union and 3/4" x 1/2" sweat copper X cup reducer( it will be tubing size and fit into the union tubing half). Have a shop vac suck the water out pipe before soldering. Water will carry the heat away. Blue Monster thread sealant my go to telfon tape.

 

[GReynolds929]

Is this for a boiler or your potable house supply. The existing PRV and backflow look like they are for a boiler auto fill. The T3 cast iron setup is for a boiler and not potable system. The T3 with a brass body is for potable use.

 

[mcat]

Is this for a boiler or your potable house supply. The existing PRV and backflow look like they are for a boiler auto fill. The T3 cast iron setup is for a boiler and not potable system. The T3 with a brass body is for potable use.

My appologies I omitted this detail, it's for a boiler, not the potable house supply. There is a T fitting further back that feeds the potable house supply. What I am discussing is for the boiler which is a forced hot water heating system ( weilMclain )

 

[mcat]

Wasn't nearly as a bad as I had thought. Cut out the old valve and added two quarter turn ball valves to shut off the supply to a gas potable hot water heater and the other to the forced hot water heating boiler. From there I installed the Taco 334-T3 and put everything back together.

Thanks to everyone's insight and helpful tips, it was much appreciated!
( I do have a drain tube installed on the 334-T3 - this was just a photo I took prior to wrapping up )

 

[Fitter30]

Looks like your on the right side of a unfinish basement. I'd to run it to a drain could use a street ell off the relief to keep it high. More than likely wouldn't have a problem but with a finish space wouldn't take that chance since its relieves at 30 lb.

 

[mcat]

Looks like your on the right side of a unfinish basement. I'd to run it to a drain could use a street ell off the relief to keep it high. More than likely wouldn't have a problem but with a finish space wouldn't take that chance since its relieves at 30 lb.

Yep that's exactly what I did do actually. I ran the pipe down to a drain further off to the side. Ironically all the relief valves just empty to the floor, boiler, the old Taco valve I just replaced and the hot water heater. Every home I've seen, this is how it's left, but this time I ran them all to a drain.

 

[Reach4]

It might be good to have a bottle cap containing an uncoated aspirin or something to collect a bit of any drainage as a detection tool. There should not be any liquid coming out over a season.

 

[mcat]

It might be good to have a bottle cap containing an uncoated aspirin or something to collect a bit of any drainage as a detection tool. There should not be any liquid coming out over a season.

Are you thinking along the lines of adding a T fitting on the way down from the drainage valve with a 90 that could have a small plastic container and the asprin or something to indicate moisture? If I add a cap direct to the drain wouldn't that just blow off due to the pressure if it ever got above 30psi?

3 days and so far so good no leaks, no moisture no liquid so far. I agree that the drain lines all being connected to a drain don't really have any way to indicate what is leaking.

 

[Reach4]

I was picturing the pipe dumping above the drain grate, and the old bottle or jar cap being on the grate. Even a piece of paper could record that it had been wet.

 

[mcat]

I was picturing the pipe dumping above the drain grate, and the old bottle or jar cap being on the grate. Even a piece of paper could record that it had been wet.

Perfect! Much simpler and not so over engineered like I was thinking