Tempering/Mixing Valve Watts

Old 04-08-05, 12:16 PM
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Arrow Tempering/Mixing Valve Watts

HI Gang, my domestic hot water is from the boiler coil. My Watts model 70A mixing valve 120-160* sprang a leak. I removed the top plastic adjustment knob and when I put the wrench on the nut underneath the knob to give it a bit of a turn, all water (heck) broke loose. After going to the Watts Valve page of items of this kind, I realized that this was never the type of valve to prevent scalding. I looked at the Watts MMV-US 1/2" mixing valve 90*- 130* and thought that this was much safer and probably code compliant. The only problem is that it takes our local plumbing supply house here in town until Monday to get one. I can wait. Am I on the right track with deciding to change the model of the valve? THANKS!
-Bob p.s. the new valve is about $80.00
Old 04-08-05, 04:35 PM
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In theory

You are right. The few that I have installed, I've had to remove due to complaints of low water temperature. If all of your domestic lines are insulated well, you might be ok. For my money, I'd rather see anti-scald faucets. This is one reason I'm a big advocate of indirect water heaters.
Old 04-08-05, 09:39 PM
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Bang on

Bingo on the antiscald faucet...

Since you're changing out the valve...now would be a good time to ask if you're happy with the fixture flow rate...most manufacturers offer different valve Cv's (tells how much pressure drop to expect at a specific flow). Without getting into the technical aspects of valve Cv it essentially means the larger the CV the less pressure drop. (By the way the pipe connection to the valve has nothing to do with the Cv as is commonly mistaken. Most control valve manufacturers offer several different Cv's in the same connection size)

So if the replacement valve has a smaller Cv then there will be more pressure loss through the valve thus less flow to your fixtures.

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