Outdoor water hydrant

Hello,
I am going to install (2) outdoor water hydrants on my property. They are the kind that will not freeze during cold weather. I have previously run the underground water lines around the footings of my attached 3 car garage a few years back when I built the garage. All I have to do is locate the two points on the line that I previously arranged to be the attachment points. I know that there are 2 types of hydrants made, one called a sanitary hydrant and the other one just a regular. The sanitary does not let the drained off water mix with the ground water. A lot of counties require these type to be used by law. However, they are around $500 dollars each and the regular type can be bought for a hundred or so. The reason counties require the sanitary type is to eliminate the possibility of getting ground water sucked back in to the house water lines. Now my question....I have been told that I could use the regular type with no problems if I put "this valve" (I can't remember it's name) in the water line between the house and the hydrants. It is supposed to keep any water from flowing back into the house water lines. Can anybody tell me the name of this device and maybe some more information about it and it's operation ? This would be greatly appreciated!!!
Thanks
Drainplug

valve

A double check backflow preventer is NOT the one to use in your situation. Depending on your local codes you will either need a "pressure type" backflow preventer, or a reduced pressure principal backflow preventer. Either one will be installed between your hose valves and the main line connection. There is a good chance your line should have one installed anyway depending on what you have in the garage and how it is connected to the water system.

What's wrong with using "double check backflow preventer" along with a "water hammer stub" to prevent pressure build up?

The unit I have has a brass housing and a molded plastic module that is inserted into it.

The module appears to have two check valves and each one looks like it could handle the full pressure.

Edit:
A photo of the one I have.
http://www.longrange.net/R0010015.JPG

Does it look like the right type?

The water hammer stub won't work long?

Now I'm really confused

Hey HJ,
Now you have me really confused......Bill Arden responded that I should use a "double check valve backflow preventer" and that is the name of the device that a plumber friend of mine had suggested that I couldn't remember !!! Now you say that that won't work...that I should use either "a pressure type backflow preventer" or "a reduced pressure principal backflow preventer. I have researched the "double check valve backflow preventer" online and to me(I'm not a plumber) it sounds like it should work and it's purpose is exactly a fix for my problem...but like I said, I'm no expert. You mentioned something about any other water needs in the garage, well, there is none. I bit into the 3/4" water line in the basement, put in a shut-off valve and ran it out through the block wall to feed the plastic well -type pipe I used to run underground. I want to place two hydrants, so this pipe comes out of the back wall of my basement, runs underground along the back wall of the garage, comes around the end of the garage and up along the front wall of the garage. I will have one hydrant in the rear yard behind the garage and one in the front yard area, near my main driveway. The device that I came up with to buy is made by Watts, model 007M3QT, around a hundred dollars. Can you explain why this won't work or suggest the exact brand and model number of something that will work correctly for my situation. Thanks, I can use all the help I can get !!!!!!!
Drainplug

That one looks expensive.
How about watts Cu7-U2 0064041 ?

I think the problem is how the pipe to the garage is defined.

The pipe to the garage has to be defined as "not a health hazard"

This means that the faucets need vacuum breakers, but this is typically included in the design of "drain back" faucets.

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I don't know what the code says, but the concept is to prevent any water from flowing back into the house.

Since check valves are never perfect, I am not sure how this is possible unless the valve sensed the drop in house pressure and discharged water from the garage pipe into a drain.

I suspect that is why these valves are defined as "not for use where there is a health hazard".

Adding pressure reduction or even a vacuum breaker between the check valves will NOT reduce the risk if the house pressure is dropped to zero during a draining.

Edit:
There is a code difference between "Unhealthy" and a "health hazard"
For example standing water that stays in the pipes of a fire sprinkler system is defined as "Unhealthy" even though as a sealed system there is no way for bacteria to get into the pipes.

valve

Go to Home Depot, or a similar store. Look in the lawn irrigation aisle. They will have a Watts pressure vacuum breaker/backflow preventer. That is the one you need, and it is the minimum you should be permitted to use. The double checks are sometimes used on swimming pool fill valve feeds but only because they are easy to install.

Now I'm confused. I wonder what happened to my first post where I mentioned HomeD?

1. You can't use a hose fitting check valve since that would prevent the valve from draining properly.

2. You have to have a vacuum breaker AFTER the valve to prevent the water in the hose from being sucked back into the drain.

3. Adding a "vacuum breaker" to the "backflow preventer" that is at the house shutoff valve won't do anything since the pressure will never be negative at that point during normal use.

The worst "use case" would be a draining of the house water supply without draining the exterior faucets. In this scenario the "backflow preventer" has to keep the full water pressure from flowing backwards.

I think the addition of the "vacuum breaker" to the "backflow preventer" is done to prevent problems in muti-story buildings where you could get full vacuum at spots during a drain.

My suggestion. (Note: I don't know the code)

1. Go with the brass case "backflow preventer" from the plumbing isle.
Here is the one I used: http://www.longrange.net/R0010015.JPG

2. Make sure you have "vacuum breakers" after the faucet valve.
They make small add-on ones in the garden hose isle if the faucet does not have one built in. (mine has it built in)

Edit:
There is one "use case" where adding a "vacuum breaker" to the "backflow preventer" helps. If the unit is installed in a 3rd story and you drain both the house and the garage, the "vacuum breaker" prevents a "slow suck" that could cause tiny amounts of water to come back into the house over several weeks.

But since the external faucets are unlikely to be drained every time the house is, it is still the worst case and thus having a "vacuum breaker" at the "backflow preventer" does not help.

The correct device to employ may very well be a RPZ (Reduced Pressure Zone device), which is like a double check on steroids. No other device can be cut into the basement plumbing, and be rated to protect from toxic backflow from downstream waterlines that are at the same elevation or higher than than the backflow preventer. Look at a Watts 009 for one example. The drawback, besides cost, is that the RPZs can briefly squirt water when downstream flow shuts off with a bang. You might have to fit the RPZ with a drain fitting, and pipe it to a sump.

The answer to "Why an RPZ?" would be the assumption by code, that the soil and ground water in it, be considered toxic. An RPZ device can also be called a Reduced Pressure Principle Backflow Prevention Assembly

Bill Arden

The "vacuum breaker" is intergral to either a pressure backflow preventer or an RPPBFP unit. It is not just for multistory buildings, and IS to prevent reverse flow when the upstream supply pressure is interupted. The double check is NOT approved for a system like this, AND once the proper control device is fitted, the individual hose vacuum breakers ARE NOT required. And, Home Depot was mentioned because that is one place where he can get the proper unit if he goes to the correct department, and not the plumbing section.

For the small cost difference it is best to buy the correct unit.

Note: You will still have to have to either remove hoses OR add a vacuum breaker at the faucet to keep it from freezing.