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Old 10-11-2013, 09:54 AM   #1
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vacuum breaker question


Hi,

I am kind of confused about the issue of a vacuum breaker. From what I understand it prevents back flow of water into the plumbing system and syphoning. I read that it causes the water to flow backwards in the supply lines. If that is correct I don't understand how contaminants can get in the water supply? The water supply and the draining lines are separate. If someone could please explain I would appreciate it. Also, I realize it lets air into the system to allow positive pressure for drainage.

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Old 10-11-2013, 10:10 AM   #2
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For example... If you were to run your hose and drop it in your pool to add water. And there was a possible back pressure it could siphon the water out of your pool and into the water supply system and create a contamination. many people like to hook up a hose in their laundry / utility sinks and leave them in there. If your sink were to back up / fill up and there was a back pressure it could siphon that water / sewage into your water supply system. I guess I can go on and on about different examples but that's the jist of it.

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Old 10-11-2013, 10:33 AM   #3
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For example... If you were to run your hose and drop it in your pool to add water. And there was a possible back pressure it could siphon the water out of your pool and into the water supply system and create a contamination. many people like to hook up a hose in their laundry / utility sinks and leave them in there. If your sink were to back up / fill up and there was a back pressure it could siphon that water / sewage into your water supply system. I guess I can go on and on about different examples but that's the jist of it.
Ok I get that. No air behind water (venting) can cause back pressure but what else could cause this to happen?
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Old 10-11-2013, 10:37 AM   #4
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For example... If you were to run your hose and drop it in your pool to add water. And there was a possible back pressure it could siphon the water out of your pool and into the water supply system and create a contamination. many people like to hook up a hose in their laundry / utility sinks and leave them in there. If your sink were to back up / fill up and there was a back pressure it could siphon that water / sewage into your water supply system. I guess I can go on and on about different examples but that's the jist of it.
I see online some people have vacuum breakers on the cold intake line going into the hot water heater. How would that help in that instance? Also when your draining your water heater do you keep the facuets open?
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Old 10-11-2013, 06:38 PM   #5
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vacuum breaker question


I think you are confusing a vaccum breaker and a backflow preventer. A backflow preventer is a one way valve that is intended to be used where the water on one side of the valve is potable, and the water on the other side is not. For example, your boiler makeup water usually comes from the the potable cold water line in your house. If the pressure in the boiler happened to be higher than the pressure in the makeup line, and you did not have a backflow preventer, contaminated water from the boiler could flow into the cold water line.

Similarly, an outdoor connection to the sprinkler system should have a backflow preventer, since sprinkler water can become contaminated.

A vacuum breaker is intended to prevent development of a vacuum in an appliance. My water heater has a vacuum breaker, which is intended to allow air to enter the water heater when it is drained. This is intended to prevent collapse of the tank due to lower than room air pressure in the tank. Vacuum breakers are commonly used in pipes which could develop low pressure when they are drained.
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Old 10-11-2013, 09:22 PM   #6
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vacuum breaker question


A break in the city water main is the usual cause.

A few historical ones.
1923-001 Washington
A typhoid fever epidemic, that resulted in two deaths, was caused by contaminated river water pumped from a lumber mill's auxiliary water supply into the public water mains.
1933-001 Illinois
At the 1933 Worlds Fair, an epidemic of dysentery spread among the visitors, of the eight hundred identified victims, more that forty died. Backsiphonage through "generally defective water and sewerage piping layout" in a hotel was attributed as the cause of the disease outbreak.
1936-001 Vermont
Typhoid bacilli contaminated river water enters city water system through a by-pass maintained solely for fire-fighting purposes, causing the death of a youth.
1938-001 Midwest
University students in a laboratory drank water contaminated with brucella causing severe illness and one death.
1942-001 Kansas
An open valve on a frostproof hydrant permitted sewage from 10 families to enter the water main.
1944-001 Oklahoma
The valve of the main water supply was turned off each night at a school to conserve water causing atmospheric pressure to move waste water into drinking supply.
1947-001 Nebraska
Following a fire, a connecting valve in a pump house was left open allowing river water to enter a school's domestic supply.
1964-001 New York
A pipe to a beverage machine at a golf and country club was connected to the recirculating hot water system containing lye and chromate.
1964-002 Michigan
Backsiphonage from unprotected autopsy table contaminated hospital water.
1965-001 California
Irrigation of a field with undisinfected sewage, in a city whose potable water system is supplied by 12 deep wells, causes at least 246 cases of gastroenteritis.
1967-001 Washington
A cross connection between a gasoline pipeline and the city water system resulted in about 2000 gallons of gasoline entering the water system.
1967-002 New England
A bubbler connected to a fire protection system instead of fresh water line causes seven cases of infectious hepatitis.
1968-001 Washington
A maintenance man ingested water containing sodium dichromate after the contamination of a school's water system by a boiler chemical treatment compound.
1969-001 Arizona
An arsenate based herbicide was backsiphoned into the municipal water system following a water main break.
1969-002 Massachusetts
83 football team members and coaching staff were stricken with infectious hepatitis by drinking water contaminated by a backsiphonage incident.
1969-003 Connecticut
University football team members stricken with infectious hepatitis through irrigation water backsiphonage.

Last edited by Ghostmaker; 10-11-2013 at 09:26 PM.
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Old 10-11-2013, 09:26 PM   #7
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vacuum breaker question


1970-001 Ohio
An open valve at a wine distillery resulted in the backflow of sparkling Burgundy wine into the city water main.
1971-001 Washington
Bacteriological contamination of the community water system would periodically occur following the backflow of stagnant water from an abandoned pressure tank and plumbing system.
1972-001 Washington
The failure to disconnect an air line used to purge exposed water lines during cold weather resulted in air being pumped into the water distribution mains.
1972-002 Arizona
With a loss of water pressure, the pesticide CHLORDANE was backsiphoned through a submerged garden hose into the water distribution system.
1972-003 British Columbia
River water, drawn by an automatic pump, was forced past a check valve into the potable water system of a mill.
1973-001 Washington
Upon the opening of a fire hydrant, the Seattle Fire Department discovered diesel oil in the water; the result of a cross connection between and the hydrant drain and the sewer.
1973-002 New Jersey
A break in a 24-inch water main resulted in CHLORDANE being backsiphoned into the distribution system.
1973-003 Ontario
The water piping in an industrial mall was contaminated through the backflow of a cleaning solvent from an automotive coating shop.
1973-004 Massachusetts
A faulty check valve in a greenhouse allowed fungicide to be injected into city water system.
1974-001 Illinois
Water system contamination resulted from the backsiphonage of the herbicide Balan from a trailer mounted tank being filled by means of a garden hose.
1974-002 Washington
The high rate of flow caused by the activation of a fire deluge system reduced pressure in a domestic water line at the Sea-Tac Airport to below atmospheric causing the backsiphonage of a chemical De-Germ and other pollutants into the potable water system.
1974-003 North Carolina
The backflow of a boiler treatment chemical into the water system caused several children to become ill after consuming contaminated soft drinks at a fast food restaurant.
1974-004 New York
Twenty employees became ill as result of consuming water contaminated with a chromate solution through a cross connection with the building's air conditioning system/make up system.
1974-005 Massachusetts
The backsiphonage of a chromium compound from the chiller water of an air conditioning system contaminated the drinking water system in the auditorium housing the 94th Annual American Water Works Association Conference and Exposition.
1974-006 Massachusetts
Cross connection between dockside potable water and ship's salt water line.
1975-001 Massachusetts
Ethylene glycol from solar heating system enters potable water line.
1975-002 Washington
During the filling of a portable toilet company's tank truck, a solution of soap and formaldehyde was siphoned into a customer's water line service.
1976-001 Washington
The contamination of a small public water supply system was caused by the backsiphonage of the pesticide Endrin from an applicator's tank truck during filling.
1976-002 Tennessee
Water system contamination resulted from the backsiphonage of the insecticide Chlordane following a break in a city water main.
1976-003 Oregon
Water fountains in the State Capitol Building were contaminated with freon gas from a ruptured heat exchanger. The gas after combining with fluoride in the water supply, formed an acid compound that caused a bitter, burning taste.
1976-004 Manitoba
The backsiphonage of a fertilizer occurred when snow clearing operations knocked over two fire hydrants.
1976-005 Texas
A faulty DCVA permitted lake water to be pumped through an irrigation system into the public water supply.
1977-001 Washington
An unprotected cross connection between a closed hot water heating system and the domestic water system resulted in the backflow of Borate-Nitrite from the heating boiler.
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Old 10-12-2013, 07:50 AM   #8
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vacuum breaker question


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Originally Posted by Daniel Holzman View Post
I think you are confusing a vaccum breaker and a backflow preventer. A backflow preventer is a one way valve that is intended to be used where the water on one side of the valve is potable, and the water on the other side is not. For example, your boiler makeup water usually comes from the the potable cold water line in your house. If the pressure in the boiler happened to be higher than the pressure in the makeup line, and you did not have a backflow preventer, contaminated water from the boiler could flow into the cold water line.

Similarly, an outdoor connection to the sprinkler system should have a backflow preventer, since sprinkler water can become contaminated.

A vacuum breaker is intended to prevent development of a vacuum in an appliance. My water heater has a vacuum breaker, which is intended to allow air to enter the water heater when it is drained. This is intended to prevent collapse of the tank due to lower than room air pressure in the tank. Vacuum breakers are commonly used in pipes which could develop low pressure when they are drained.
jesus christ that is confusing. When you do drain a water heater should you leave the taps open? So, basically it the vacuum allows some air into the system to keep positive pressure when draining? Am I to assume the breaker should be placed before the shut off on the cold inlet pipe?
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Old 10-12-2013, 08:08 AM   #9
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vacuum breaker question


Older water heaters are not set up to use a vacuum breaker. As long as air can get into the tank when you drain it, you will not create a vacuum. A vacuum (mower than atmospheric pressure) can be created in a tank if you close off all the inflow lines, and drain the tank from the bottom. As you drain water out, the pressure in the tank goes down. If you were able to drain all the water out of the tank, and did not allow any air into the tank, you could effectively reduce the pressure in the tank to close to 0 psi. Air pressure at sea level is about 14 psi, so your tank could experience a pressure difference of potentially 14 psi, which would collapse most tanks.

To prevent this, some new hot water tanks, mine included, have an extra threaded hole at the top, to which you attach a short length of pipe, with a vacuum breaker threaded onto the top of the pipe. In the event that water drains from the tank, for whatever reason, the vacuum breaker allows air to flow into the tank, preventing a vacuum from developing in the tank. When you refill the tank, you leave at least one or two valves open, which allows the air in the tank to escape during the filling process. So far as I know, air will not escape out through the vacuum breaker, think of it as a one way valve for air that allows air into the tank when the tank pressure drops below atmospheric. This is an inexpensive item, as I recall I got a Watts vacuum breaker for less than $20.

As I noted before, the vaccum breaker is different than the backflow preventer. I have a Watts backflow preventer (one-way valve) on my boiler makeup water line, cost about $30 including a pressure reduction valve which limits the pressure in the boiler to about 15 psi. There is no vacuum breaker on my boiler, but my boiler is over 50 years old, so possibly modern boilers have such a device.
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Old 10-12-2013, 08:30 AM   #10
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Originally Posted by Daniel Holzman View Post
Older water heaters are not set up to use a vacuum breaker. As long as air can get into the tank when you drain it, you will not create a vacuum. A vacuum (mower than atmospheric pressure) can be created in a tank if you close off all the inflow lines, and drain the tank from the bottom. As you drain water out, the pressure in the tank goes down. If you were able to drain all the water out of the tank, and did not allow any air into the tank, you could effectively reduce the pressure in the tank to close to 0 psi. Air pressure at sea level is about 14 psi, so your tank could experience a pressure difference of potentially 14 psi, which would collapse most tanks.

To prevent this, some new hot water tanks, mine included, have an extra threaded hole at the top, to which you attach a short length of pipe, with a vacuum breaker threaded onto the top of the pipe. In the event that water drains from the tank, for whatever reason, the vacuum breaker allows air to flow into the tank, preventing a vacuum from developing in the tank. When you refill the tank, you leave at least one or two valves open, which allows the air in the tank to escape during the filling process. So far as I know, air will not escape out through the vacuum breaker, think of it as a one way valve for air that allows air into the tank when the tank pressure drops below atmospheric. This is an inexpensive item, as I recall I got a Watts vacuum breaker for less than $20.

As I noted before, the vaccum breaker is different than the backflow preventer. I have a Watts backflow preventer (one-way valve) on my boiler makeup water line, cost about $30 including a pressure reduction valve which limits the pressure in the boiler to about 15 psi. There is no vacuum breaker on my boiler, but my boiler is over 50 years old, so possibly modern boilers have such a device.
Aren't backflow devices on the waste drain lines?
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Old 10-12-2013, 08:32 AM   #11
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vacuum breaker question


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Originally Posted by Daniel Holzman View Post
Older water heaters are not set up to use a vacuum breaker. As long as air can get into the tank when you drain it, you will not create a vacuum. A vacuum (mower than atmospheric pressure) can be created in a tank if you close off all the inflow lines, and drain the tank from the bottom. As you drain water out, the pressure in the tank goes down. If you were able to drain all the water out of the tank, and did not allow any air into the tank, you could effectively reduce the pressure in the tank to close to 0 psi. Air pressure at sea level is about 14 psi, so your tank could experience a pressure difference of potentially 14 psi, which would collapse most tanks.

To prevent this, some new hot water tanks, mine included, have an extra threaded hole at the top, to which you attach a short length of pipe, with a vacuum breaker threaded onto the top of the pipe. In the event that water drains from the tank, for whatever reason, the vacuum breaker allows air to flow into the tank, preventing a vacuum from developing in the tank. When you refill the tank, you leave at least one or two valves open, which allows the air in the tank to escape during the filling process. So far as I know, air will not escape out through the vacuum breaker, think of it as a one way valve for air that allows air into the tank when the tank pressure drops below atmospheric. This is an inexpensive item, as I recall I got a Watts vacuum breaker for less than $20.

As I noted before, the vaccum breaker is different than the backflow preventer. I have a Watts backflow preventer (one-way valve) on my boiler makeup water line, cost about $30 including a pressure reduction valve which limits the pressure in the boiler to about 15 psi. There is no vacuum breaker on my boiler, but my boiler is over 50 years old, so possibly modern boilers have such a device.
So, to prevent a vacuum when draining the tank I should leave at least 2 faucets open?
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Old 10-12-2013, 08:45 AM   #12
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So, to prevent a vacuum when draining the tank I should leave at least 2 faucets open?
You only need to open one. As long as air can get into the pipes, you will be OK. One the level in the tank drops, you can open the pressure relief valve to allow more air into the tank.
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Old 10-12-2013, 08:51 AM   #13
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You only need to open one. As long as air can get into the pipes, you will be OK. One the level in the tank drops, you can open the pressure relief valve to allow more air into the tank.
but if I open the pressure relief valve then water will spill out of the copper pipe its attached to.
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Old 10-12-2013, 08:56 AM   #14
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It should be low enough where that wont happen. Very little if any.
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Old 10-12-2013, 08:58 AM   #15
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How can you even tell when the water level is low enough to open the pressure relief valve?

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