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Thread: classic reverse water hammer...maybe

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    DIY Junior Member clax66's Avatar
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    Default classic reverse water hammer...maybe

    After reading many posts on here it looks like I have the symptoms of reverse water hammer. It is in my upstairs bathroom just after a long run of plumbing. It typically happens first thing in the morning when I turn on the cold water. It flows for a second or two then I get a bang-bang-bang and the water stops. If I flush the toilet first this doesn't seem to happen. My question is, will installing a engineered hammer arrestor stop the hammer or is it possible to be a number if things that all combine to create the problem? Recently I had my 1/2" water main upgraded to 3/4" and I probably have more water pressure than I used to. Would I possible need something to reduce the water pressure and a hammer arrestor?

    Andrew....

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    DIYer, not in the trades LLigetfa's Avatar
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    Quote Originally Posted by clax66 View Post
    It flows for a second or two then I get a bang-bang-bang and the water stops.
    The water stops? That is not "reverse water hammer".

    Sounds like you have a closed system without an expansion tank and the pressure creeps up overnight. It also sounds like you have a loose washer on the tap.

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    DIY Junior Member clax66's Avatar
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    Quote Originally Posted by LLigetfa View Post
    The water stops? That is not "reverse water hammer".

    Sounds like you have a closed system without an expansion tank and the pressure creeps up overnight. It also sounds like you have a loose washer on the tap.

    I am sorry, i am not sure what 'closed system' is. I thought I had a typical plumbing system with an incoming water line having branches off of it for various plumbing fixtures. Aside from the loose washer is there anything i can do?

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    Moderator valveman's Avatar
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    If you don’t have a pressure reducing valve or a check valve on the incoming water line from the city, then your system is not “closed” to the city system.

    Upstairs, long run, I suspect air accumulating in the high spot. Do you notice any air coming out when you open the faucet?

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    Moderator & Master Plumber hj's Avatar
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    Default hammer

    REverse water hammer does NOT stop the flow. At least not so you would notice it since it happens within milliseconds of opening a faucet. What you WOULD notice would be a loud bang, or maybe a couple, as soon as the faucet was turned on, NOT after the water has been flowing for even a short while. Without doing our own tests while it is happening, there is no way we can diagnose it.
    Licensed residential and commercial plumber

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    Retired Defense Industry Engineer jadnashua's Avatar
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    The most likely thing is a loose seal that is a little sticky...things open up, then it slams itself shut in the water stream. Any device with a washer could be the source including the main shutoff valve to the house.
    Jim DeBruycker
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    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    DIY Member WorthFlorida's Avatar
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    Quote Originally Posted by clax66 View Post
    ...Recently I had my 1/2" water main upgraded to 3/4" and I probably have more water pressure than I used to. Andrew....
    A long shot; After the 3/4 line was installed there might have been some junk inside the tubing. Pieces of junk or perhaps solder has itself jammed up the the valve of the faucet or the shut off valve. I would shut the water off at the main and remove both the shut off valve stem for the sink cold water and the faucet valve stem. Inspect these parts. If they look OK have someone slowly open (just a crack) the main so the line can be flushed. Use a pail or bowl to catch the water to see of anything came out. Also take off the faucet aerator and check it.

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    DIY Junior Member clax66's Avatar
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    The main shutoff is a 1/4 turn ball valve. I am guessing this would not have a washer. The faucet in question has a cold water tap and a hot water tap. the spigot is loose due to a broken nut that holds it tight to the counter. I like the idea of flushing the system, checking the aerator for any debris and changing out the cartridge insert for the cold water tap including the washer.
    It still seems odd that it only happens first thing in the morning and only if the faucet is the first thing that is used. No air comes out ever.

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    DIY Member WorthFlorida's Avatar
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    As jadnashua mentioned above "a loose seal"? If the faucet is a typical stem with a flat washer, the screw that holds it could be loose or the washer is just worn out. Maybe there is something in in the valve and as it sits for a long time is may move around and when you turn is on, water flows then it move to a position that blocks the water flow. I assume that by closing the tap then opening it that it starts to work OK. If the faucet has a broken nut as you mention, just replace the faucet. They're not that expensive and about the easiest thing to replace. Don't get any for less than $50 (USD). They're all plastic and won't last. Ones in the $125-$200 range are usually very good. If you doubt your skills, time to call a plumber.

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    DIYer, not in the trades LLigetfa's Avatar
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    Quote Originally Posted by clax66 View Post
    It still seems odd that it only happens first thing in the morning and only if the faucet is the first thing that is used. No air comes out ever.
    I don't recall you clearing up whether or not this is a closed system. On a closed system, the pressure can increase due to expansion, so if it is the first use, it is subject to this higher pressure.

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    DIY Junior Member clax66's Avatar
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    First of all, thanks for all suggestions and input.

    Quote Originally Posted by LLigetfa View Post
    I don't recall you clearing up whether or not this is a closed system. On a closed system, the pressure can increase due to expansion, so if it is the first use, it is subject to this higher pressure.
    There is no pressure reducing valve or a check valve on the incoming water line from the city so i must have an open system. Is it necessary or advised to have one of these? I don't see how the pressure can get any higher in the house than what the city pressure is. I could always throttle the water coming in with the ball valve to lower the pressure a bit....

    As to replacing the faucet, I am all for it but my wife seems to like her Perrin & Rowe Georgian

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    DIYer, not in the trades LLigetfa's Avatar
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    Quote Originally Posted by clax66 View Post
    There is no pressure reducing valve or a check valve on the incoming water line from the city so i must have an open system. Is it necessary or advised to have one of these?
    Toronto has had a by-law on the books since 2007 requiring backflow preventers.

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    Retired Defense Industry Engineer jadnashua's Avatar
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    If you have a closed system, after using hot water from the heater, then shutting the valves, the cold, dense water in the tank gets heated, lighter, and it expands. This creates higher pressure in the system. In this case, an expansion tank is required to keep the pressure in line. A simple check is to pick up an inexpensive, screw-on pressure gauge with a second, tattle tale hand and leave it connected for say 24-hours. It will record the peak pressure. FWIW, partially closing a supply valve will NOT change the static water pressure, but could significantly affect the volume available. While there is a connection between pressure and volume, they are not the same thing! A fire hose and a soda straw could have the same pressure, but you'll get a lot more water from the fire hose than a soda straw when you open up the valve.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    DIY Member WorthFlorida's Avatar
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    Quote Originally Posted by clax66 View Post

    As to replacing the faucet, I am all for it but my wife seems to like her Perrin & Rowe Georgian

    They're really nice faucets and real good quality. I still think something is blocking the flow or the valve stem is damaged. Here is a site with a good picture of a replacement valve. <http://www.chicagofaucetshoppe.com/Rohl_9_13145_p/roh-9.13145.htm> Nice brass quality and you can see that it is not a flat washer type. You might be getting high pressure overnight and maybe when you first open the valve, this high pressure is moving something that blocks the water. When no water is flowing the pressure is the same on both the hot and cold lines. With water flowing the hot side maybe a little lower since it goes through more plumbing. Therefore, if the hot side doesn't have the problem, the toilet has no problem, it has to be in the faucet. Going after the presumed high pressure issue will not fix the problem. If you want to try something, at night on another faucet, just open the cold water side so the water just flows (after a drip). This will prevent any high pressure from building up. Or you can open up an outside spigot and do a drip flow over some plants. Then try to sleep on it but you'll be up all night waiting for the morning test.

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