Sprinkler Winterize, Backflow Preventer dilemma

Discussion in 'Irrigation / Sprinkler Forum' started by mfmccoy, Sep 21, 2010.

  1. mfmccoy

    mfmccoy New Member

    Sep 21, 2010
    I have a small dilemma and I am wondering if I am going to need to call in a plumber.

    I am planning to blowout my sprinklers at the end of the season on my own and I thought I would do a little research to make sure I am doing it right. Through the various blogs and the how-tos I have discovered that you must not blow out your sprinklers through the backflow preventer because it will melt the rubber gaskets. This makes complete sense, however, when I refer to the setup I have at home I have found that the hose bib (where I have planned to connect my air hose) is before the backflow device which essentially means that I will be blowing air up through the backflow and down the line to the sprinklers. On top of that I will be forcing air down the main waterline, although closed inside the house, it is still a concern that the constant air might do some damage.

    So my question is... am I OK to blowout my sprinklers as is or am I going to need to call in a plumber to remove the hose bib and move it so it is after the backflow device? :confused:

    Thanks for any help people can provide to me.
  2. rfrrace

    rfrrace New Member

    Jul 4, 2011
    Don't worry about the PVB, it can take a lot more than you think. If you have an RPZ (not common in MN for residences) I would blow after it. Your inside pipes can take a lot as well. Just regulate your compressor output to blow out the sprinklers with slightly more pressure than normal water pressure. Be sure to drain back to the main shut off. Go thru the zones at least twice, open and close the little check ports as well while blowing and be done with it. I usually close both ball valves on the PVB when done. If your inside shut-off valve is a gate type valve, be sure to get it shut off tight. They have a tendency to leak after a few years. If you are not sure of the valve's condition ,leave the drain open and hang a bucket under it thru the winter.
    Hope this helps. I know many guys do it different, but this has worked for me for many years.
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  4. Gary Swart

    Gary Swart In the Trades

    Sep 1, 2004
    Yakima, WA
    Here's how I do it and it works quite well although slower than having someone with the big industrial air compressors do it. I remove the backflow preventer and store it inside. Reason being, there is a possibility that a small amount of water might remain inside of it. I made an adapter that connects my air hose to the pipe where the BFP was. I then blow each zone separately, using 2 sixty gallon tanks of air per blow. I shut the air off while the tank recharges. The big boys would do this with one blow for the whole system in just a very few minutes, but it would cost $50 or more. My time is mine own, I own the compressor already, so it's $50 not coming out of my pocket. I can't address your question with facts about blowing through the BFP, but I don't thing it would hurt the BFP to do it.
  5. cn90

    cn90 New Member

    Jan 13, 2009
    Hi Gary,

    Do you have a picture of your "invented adapter"?
    I have a Watts 800 series and want to do the same!
  6. Gary Swart

    Gary Swart In the Trades

    Sep 1, 2004
    Yakima, WA
    Sorry I didn't see this post until today. No pic, but it's just half of a 1" union (to match the one on the "out" pipe) and adapters reduce and connect to a 1/2" ball valve then to an air hose quick connect. No quite a Rube Goldberg contraption, but close. I use the valve so that I can rebuild the air supply without going to the compressor. My compressor is stationary in the back of a store room adjacent to my shop and the shop is plumbed with 1/2" copper pipe and has air outlets spaced around.

    Here is more specific information. I used half of a 1" union to mate with the other half which is on the outlet pipe. Then I screwed a 1" to 1/2" female adapter to the union, soldered a short 1/2" nipple to the adapter, soldered the other end to the 1/2" ball valve. To the other end of the ball valve I sweat another short 1/2" nipple and to the other end of that, a 1/2" female adapter. Then I just screwed a quick connect for the air hose into that.
    Last edited: Oct 27, 2011
  7. cn90

    cn90 New Member

    Jan 13, 2009
    Thanks Gary for the tip.


    I just installed a hose bib just downstream of the Backflow Preventer, see #4 in the picture.
    This hose bib is used strictly for Sprinkler Winterization.
    Actually this port (#4) is the recommended port for blowout procedure, although the reality is different as 99% of the homes out there do not have this port, read on.

    Couple of notes for those who are new to this Sprinkler Winterization procedures.

    1. When you hire a Company to winterize your Sprinkler system, and since 99% of the homes out there do not have port #4, they blow air through ports #1 or #2, not a recommended port but since they use low pressure (less than 80 psi and has high volume tank), the risk to the Float Disk is low.

    2. If you decide to do this at home using shop air compressor (the standard 2-3 gallon type), there is a way to do this:

    a. If you don't have port #4 and want to blow through port #3, it is tricky because once air pressure is below 20-30 psi, the Float Disk drops down as there is no water and the pressure is low.
    Remember the Float Disk needs water to float!
    - Once the Float Disk is down, it is virtually impossible to blow it back up using air!
    - To over come this issue:
    ---> I remove the Float Disk
    ---> Use a small spring (Home Depot) below the Float Disk, and re-install the Float Disk to keep it tight against the housing so there is no air leak.
    ---> Now you can winterize the system.
    ---> Just remember to remove the Spring later.

    However option b) below is better:

    b. This weekend, I just installed a hose bib just downstream of the Backflow Preventer, see #4.
    It is very easy with a Propane Torch and about 1 hour.
    If you have done plumbing before then it is easy.
    Otherwise get a plumber to install this for you.
    Now I winterize via this hose bib in port #4.

    The detail on how to make the adaptor (where it fits between the hose bib and the air compressor) is in this thread:


    Last edited: Nov 1, 2011
  8. Gary Swart

    Gary Swart In the Trades

    Sep 1, 2004
    Yakima, WA
    The procedure outline very well by cn90 may be absolutely correct for the BFP he uses and that is shown. However, this is not the only type of BFP device used. My BFP is a Wilkins 950 double check and has a much different configuration than the one show here. To my way of thinking, installing a second union and making the BFP removable and putting it in warm storage for the winter makes drying it unnecessary and would be just as easy as installing the hose bib. This would work for any type of BFP. Certainly do whatever you are comfortable with.
    Last edited: Oct 31, 2011
  9. Larrysi

    Larrysi New Member

    Sep 23, 2015
    Framingham, Massachusetts
    New house, first sprinkler system. Prefer to winterize my own, and here is a picture of my setup. Thinking I can blowout of #3 with an adapter replacing the drain.

    If not, I think i have to put something new around 4. I partially think a union so I can remove the backflow preventer, but around here it seems like people just leave them on this winter (just outside boston). Or do a hose bib like the diagram from the guy before me.

    Anyone know if #3 is ok? It is past the backflow preventer, so I would think it would be the easiest.

    thanks for the help. appreciate it.

    Attached Files:

  10. valveman

    valveman Cary Austin Staff Member

    Mar 15, 2006
    Pump Controls Technician
    Lubbock, Texas
    From 3 to 1 will be easy to drain. But I think you will need to find the other end of pipe 4 and open it up to get air to blow from 3 out to the inlet of pipe 4.
  11. M1x Mstr

    M1x Mstr New Member

    Sep 29, 2019
    Would this be the proper process to blow out this type of system.

    -1 shut off water in house.
    -2 open silver drain plug at the bottom of back flow.
    -3 use an adapter at that drain to blow though the back flow @ 50 psi

    Or... Would I want to blow out at the top check valve to the right of the back flow?

    There is no connection running down the white pvc piping...


    Attached Files:

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