correct me if im wrong... - Plumbing Zone

younger-plumber · 03-02-2010, 09:48 PM

if i install i prv (pressure reducing valve) in the main line of a customers houes. 3/4 inch poly. if the heater does not have an expansion tank on it then there is a very good chance that without one, it could cause the t&p valve to blow off? because without the prv the extra pressure the water heater makes can push back to the citys main but with the prv it builds up in the house and the only place it can escape is the t&p or opening a faucet.?

house plumber · 03-02-2010, 09:51 PM

I saw this exact episode on ask this old house

Plumbworker · 03-02-2010, 09:51 PM

get one with a bypass

Indie · 03-02-2010, 09:52 PM

Sounds good to me. There is a city near me that requires an expansion tank because of the check valve the city has put on the water lines.

ToUtahNow · 03-02-2010, 10:02 PM

We are required to install PRVs with by-passes to prevent that. Where that could still be a concern is when the street pressure is higher than the rating of the T&P or there is a check valve before the street.

Mark

younger-plumber · 03-02-2010, 10:10 PM

gotcha. well im not familiar with the concept of a bypass? what exactly does that do?

SummPlumb · 03-02-2010, 10:20 PM

It will not make the relief valve blow off unless your pressure + temperature exceeds the limit for the valve. If your pressure is reduced by a PRV and you don't add an expansion tank, you will get a warm sandwich of water on the cold side for a few seconds when you brush your teeth in the morning.

Someone above mentioned getting a PRV that has a expansion bypass built into it. You can do this also. I went back to adding exp. tanks b/c i got tired of explaining the different valves to moron inspectors.

ToUtahNow · 03-02-2010, 10:30 PM

Quote:

Originally Posted by younger-plumber

gotcha. well im not familiar with the concept of a bypass? what exactly does that do?

When the downstream pressure is higher that the upstream pressure it forces the excessive downstream pressure out the upstream side. Most PRVs sold include a bypass.

Mark

younger-plumber · 03-02-2010, 10:36 PM

haha. im just tryin to get some ideas on ways to make sales. aka ma'am i would reccomend putting in this expansion tank when we install your prv. just as a safety precaution.to ease both of our minds in the future of any problems that may occur. haha

Plumber Jim · 03-02-2010, 11:12 PM

Quote:

Originally Posted by younger-plumber

haha. im just tryin to get some ideas on ways to make sales. aka ma'am i would reccomend putting in this expansion tank when we install your prv. just as a safety precaution.to ease both of our minds in the future of any problems that may occur. haha

ah, well you need to know the city pressure before the prv and if it's over 130 i would do an expansion tank even if the prv has a bypass incase you get overnight pressure spikes.

03-02-2010, 09:48 PM	#1
younger-plumber Member Join Date: Sep 2008 Location: lynchburg Posts: 55 My Photos	correct me if im wrong... if i install i prv (pressure reducing valve) in the main line of a customers houes. 3/4 inch poly. if the heater does not have an expansion tank on it then there is a very good chance that without one, it could cause the t&p valve to blow off? because without the prv the extra pressure the water heater makes can push back to the citys main but with the prv it builds up in the house and the only place it can escape is the t&p or opening a faucet.? __________________ LIVN AND LEARNIN

03-02-2010, 10:10 PM	#6
younger-plumber Member Join Date: Sep 2008 Location: lynchburg Posts: 55 My Photos	gotcha. well im not familiar with the concept of a bypass? what exactly does that do? __________________ LIVN AND LEARNIN

03-02-2010, 10:20 PM	#7
SummPlumb Senior Member Join Date: Feb 2010 Posts: 145 My Photos	It will not make the relief valve blow off unless your pressure + temperature exceeds the limit for the valve. If your pressure is reduced by a PRV and you don't add an expansion tank, you will get a warm sandwich of water on the cold side for a few seconds when you brush your teeth in the morning. Someone above mentioned getting a PRV that has a expansion bypass built into it. You can do this also. I went back to adding exp. tanks b/c i got tired of explaining the different valves to moron inspectors. __________________ "The Plumbing Guru"

03-02-2010, 10:36 PM	#9
younger-plumber Member Join Date: Sep 2008 Location: lynchburg Posts: 55 My Photos	haha. im just tryin to get some ideas on ways to make sales. aka ma'am i would reccomend putting in this expansion tank when we install your prv. just as a safety precaution.to ease both of our minds in the future of any problems that may occur. haha __________________ LIVN AND LEARNIN

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03-02-2010, 09:51 PM	#2
house plumber HI Join Date: May 2009 Location: New Port Richey,Fl Posts: 3,084 My Photos	I saw this exact episode on ask this old house

03-02-2010, 09:51 PM	#3
Plumbworker Senior Member Join Date: Oct 2008 Location: San Francisco, CA Posts: 535 My Photos	get one with a bypass

03-02-2010, 09:52 PM	#4
Indie AAAAAAAAHHHHH!!! Join Date: Sep 2009 Posts: 3,610 My Photos	Sounds good to me. There is a city near me that requires an expansion tank because of the check valve the city has put on the water lines.

03-02-2010, 10:02 PM	#5
ToUtahNow Cruise Director Join Date: Jul 2008 Location: California/Nevada/Utah Posts: 2,414 My Photos	We are required to install PRVs with by-passes to prevent that. Where that could still be a concern is when the street pressure is higher than the rating of the T&P or there is a check valve before the street. Mark

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