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I’m installing a motorized ball valve on my main water line for automatic shutoff in case of leaks. The valve will be outdoors right after the water meter. My main water line is 3/4" copper, which transitions to PEX shortly afterward.

Here’s the valve I’m looking at:

Model: USS-MSV00072 (U.S. Solid): https://ussolid.com/products/u-s-solid-motorized-ball-valve-3-4-stainless-steel-electrical-ball-valve-with-full-port-9-24-v-ac-dc-2-wire-auto-return-normally-open-html

Specs: 3/4" NPT threads, stainless steel (SS304), PTFE ball seal, 2-wire auto return, normally open, 9–24V AC/DC, IP65.

I'm not sure what the best way to connect this to the copper pipe is. I've read that connecting copper directly to stainless steel will cause galvanic corrosion.

I've read about using brass fitting between them, but I can't seem to find any MPT to 3/4" Sweat adapters. Something like this: https://www.amazon.com/PROFLO-FEI75808-Brass-Female-Adapter/dp/B0DPJL9P6N?gQT=1&th=1 But I'm not finding many that specifically say lead-free. Is this a concern?

Should I use a stainless-steel-to-copper dielectric union instead? All of the ones I find are galvanized steel and I'm reading that stainless to galvanized contact can also have the same issues as copper to stainless. I’ve heard some people say dielectric unions can leak more than direct connections. Is that still true with modern unions?

Context:

  • This is a 1983 home, outdoor installation, before the line enters the house.
  • After the valve, the copper changes to PEX quickly.
  • I want the most reliable long-term solution with the least chance of contamination or leaks.
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    So many valves are available in brass or bronze so why use stainless steel? Commented Aug 9, 2025 at 19:01
  • The brass one on us solid says it’s not for potable water. I’m specifically looking for a motorized ball valve. Do you have any that you would recommend? Commented Aug 9, 2025 at 19:17
  • I have yet to find a suitable bronze motorized ball valve. But I did find this for brass: tameson.com/products/… However, It seems it uses CW617N for the brass and thats not suitable for potable water (contains lead) Commented Aug 10, 2025 at 21:02
  • The best option I'm finding is: valveman.com/products/3-4-bonomi-8e864lf-00 It's pricey compared to the others. But If thats the only option I'd end up going for it. If I'm understanding correctly, there isn't as much of a danger with Brass and Copper and galvanic corrosion Commented Aug 11, 2025 at 2:02
  • There are lots of valves like this, and I agree with @SolarMike, you're just using the wrong shape peg. Many valves are available in choice of stainless or brass. If yours isn't, buy a different make. Also, this valve is CHEAP, which is nice but I'm suspicious about its use as a main shutoff for your home. There are flow-sensing valves that will automatically shut off if there is a leak. They cost more but check with your insurer -- they can pay for themselves in 3, 2, even one year through substantial insurance discocunts. Commented Aug 13, 2025 at 16:28

4 Answers 4

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Dielectric unions are the go-to solution here but, realistically, If there's chlorine/fluorine in the water, you've still got an effective battery. The best thing you can do is get that stainless as far away from the copper as possible. If you've got PEX right afterwards, I'd personally make the copper/PEX transition earlier, and use a Stainless/PEX Connection (The link is just an example, buy from a trusted source) on both sides of the motorized ball valve.

I don't know what the space you're putting this in looks like. But if you go with this approach, it doesn't hurt to put more space between that stainless and copper with a loop of PEX if there's room for it.

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    This would end up putting the Pex Outdoors exposed to UV. I think the answer is to paint it in UV resistant paint or something. This does feel like the best answer though. Commented Aug 14, 2025 at 20:20
  • Yes, always opt for UV resistant paint AND a wrap if there's any chance of sunlight exposure on PEX. Commented Aug 15, 2025 at 4:57
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Another option instead of buying a motorized valve with less than ideal materials would be to use a motorized valve actuator which you can use with any normal manually operated valve. For example the Zooz ZAC36, which is rated for indoor and outdoor use.

image of motorized valve actuator attached to valve on copper pipe

Image Source

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    Your own photo? Stack Exchange policies require that images which are not the creative work of the poster be properly attributed via a link to where the image was found. Please update your posting to bring this into compliance. Commented Aug 13, 2025 at 14:09
  • I've considered this, but I don't like that its controlled wirelessly. I want something that's supposed to stop water leaks to be wired. Thanks for the suggestion though! Commented Aug 14, 2025 at 20:16
  • @DejanZelic it actually includes a wired leak probe and can be line powered with battery backup. The wireless control is just an added bonus. Commented Aug 15, 2025 at 0:07
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use 304 stainless pex fittings in your ball valve's FNPT.

have pex to and from the ball valve

the pex at whatever length to/from the valve then connect to copper or more pex

supplyhouse - boshart sspex-ma07 or ma0507

https://support.boshart.com/is-it-ok-to-thread-304-ss-pex-fittings-directly-into-copper-or-brass-plumbing-components-valves-and-fittings

you don't need to go crazy worrying about stainless to copper connections in plumbing, it's often blown out of proportion.... I've had 3/4 copper sweat to 3/4 MNPT directly into a stainless AP704 (indoor) filter housing since 2015 no problems.

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I ended up going with this instead: https://valveman.com/products/3-4-bonomi-8e864lf-00/ It's brass, lead free, and fails in place. Plus it has a manual override. Overall a much better option for what I needed

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  • Good choice, my mom uses Bonomi pneumatic valves in her greenhouses. They're a bit pricey but they are well worth the cost. Commented Aug 15, 2025 at 5:00
  • Thanks! That’s great to hear! Commented Aug 18, 2025 at 4:28

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