Pressure relief valve

[Vdawg]

Hi,

I have a home in Florida built new in 2013. I've noticed after a long, hot shower if I then open the hot water tap in the kitchen, it starts out extra forcefully for a few seconds, then goes back to normal pressure.

This made me wonder about something... In my previous house (also in Florida, built new in 2001), there was a small device that looked simply like a piece of 1/2 brass/copper that stuck out from the copper pipe where water service entered the house. It would sometimes drip water. I thought I was told it was some type of pressure relief valve. I noticed I don't have one of those on this house, and wondered if I should. If not, how would an over-pressure situation be handled? Would it use my hot water heaters relief valve to release the extra pressure?

Thanks for any info anyone can offer!

 

[Reach4]

It may have been a valve to release pressure when the water expands while heating water.

Today the thermal expansion tank, near the water heater, is how the thermal expansion is handled. That does not consume water.

 

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[Vdawg]

Thanks for your reply. My home does not have a thermal expansion tank anywhere that I can see.

 

[Reach4]

Thanks for your reply. My home does not have a thermal expansion tank anywhere that I can see.

Watch for dribbling at the T+P relief valve after a shower. However based on that symptom you posted in the first post, you may have such a tank, but have not found it yet.

There are still houses that don't have a check valve on the city water meter, so they don't need an expansion tank.

 

[Vdawg]

Thanks -- will do. If this is the type of expansion tank you're referring to, I definitely don't have this in my house.

 

[Jadnashua]

Yes, that is the most common thermal expansion tank type.

If you have a closed water supply system (One that has a check valve on the inlet from the utility or a pressure reduction valve), then you should also have an expansion tank (ET). Heating water causes it to expand...it has to go somewhere. Copper pipes don't expand, but pex, and supply hoses will somewhat. You'll see that effect on a garden hose with a nozzle at the end that has a shut off. Open the hose bib, run the hose out the spray. Close it, then shut the water off. Open the nozzle, and you'll get a spurt of water. The hose expanded slightly, and the pressure you have in the hose is from it shrinking back to it's normal elastic limit...same can happen in your house if you have a closed system.

Normally, unless something is leaking ( a toilet fill valve is a common one, but any faucet or device that has a slight leak can do it), the expansion causes the safety valve on the WH to open. That's not good for that safety valve as that can cause mineral deposits that can eventually seize it up.

Where I live, code requires all systems with a water heater to have an ET. Most utilities, if they haven't already added a check valve (this is to protect their supply from some pollutant being sucked into their supply from your home - think a hose in a puddle full of dog poop or fertilizer or insecticides) which creates a closed system. The Federal guidelines are pushing utilities to install these as maintenance is being performed on their system, which is why having an ET, even if the system isn't today closed, it will be prepared for one in the future when that work is completed.

A second, but much rarer cause of a spurt, is that the sacrificial anode in the water heater, with some water chemistry, can actually create a gas. This would cause the faucet to spurt a bit to purge that gas when you open it. If that's the case, changing the type of anode material in the WH usually solves the issue. That would tend to happen at any faucet that was opened, though. If the kitchen was the closest, it might accumulate the bulk of it, though.