Winterizing your irrigation system with a Febco 765-1 Backflow preventer

I found out recently that my new home's irrigation system was installed in the mid-eighties, and it seems most parts (the pex pipes for laterals, the 1" PVC for the run to the valves for four zones, and the backflow preventer itself) were well-built for that time.

Not much has changed—the fittings and main parts of the system are similar to what you can buy today—and the importance of winterizing the system (getting the water out of all the exterior parts) in colder climates has not been diminished!

I have a small 8 gallon 125-psi Central Pneumatic (inexpensive Harbor Freight brand) air compressor; it's not quite pancake-small, but it's no CFM (cubic feet per minute) champion, either. Rather than paying an irrigation company a bit of money to come out and use their monster compressor to blow out my system, I've MacGuyvered the process to get everything cleared out for the past few years. I want to document what I did here for two reasons: one, so I can remember all the steps in the future and avoid a half hour walking between my basement and the outdoor valves, and two, so others in a similar situation can benefit.

Adding capacity; making connections

Valve on Piggy-back air compressor setup

Here's how I set up the compressor and a 'piggy-back' tank in the basement (I run the hose through a basement window to the Febco backflow preventer):

  1. Run a hose from the air compressor outlet into a tee valve that's connected into the piggy back tank's inlet/outlet.
  2. Run another hose from the other end of that tee valve out to the Febco valve.
  3. Make sure the piggy-back tank (in my case a cheap 7 gallon tank) has it's valve completely open, and then regulate the entire system pressure using the regulator on the air compressor.

The reason I use a piggy-back tank is to provide a slight bit more CFM when blowing out the irrigation system. Note that since my compressor itself only puts out half what would be needed to blow out the system continously, I still need to blow out the lines with short 'pulses' of air, 10-20 seconds in length. Then the compressor needs to recharge before I can blow out more water.

Using a piggyback lets me blow out the system for 10-20 seconds at a time instead of 5-7 seconds at a time, effectively halving the amount of time I have to stand by the valve turning it on and off :)

Using the Febco 765-1 to blow out the system

Febco 765-1 backflow preventer valve diagram for draining irrigation system blowout
1 - Overview of the Febco 765-1

Febco 765-1 backflow preventer insides for draining irrigation
2 - Detail of the petcock and backflow preventer valve

To blow out the system:

  1. Close the upstream water inlet (below the Febco, #3 in the above picture), close the two small petcock valves on the side (#1 and #2), and open the downstream water outlet (#4).
  2. Screw air compressor NPT hose fitting to Febco valve, using teflon pipe tape to seal the threads.
  3. Run a hose from the piggybacked-compressor tanks to this valve.
  4. Unscrew the little bell cap covering the spring-loaded guts of the Febco (it uses a lock nut, so you'll need a small wrench).
  5. Turn on the compressor and regulate the pressure to 70-90 psi (don't go higher to prevent damage to your system!).
  6. Turn on one of your irrigation system zones (and leave it on).
  7. Using a small screwdriver, pull up the backflow preventer's stopper so it's touching the top of the casing (open).*
  8. While holding up the stopper, use a flathead screwdriver to open up the top small valve on the Febco and let in air from the compressor.

* Note: if you have a powerful enough air compressor, it may be able to pop up the stopper by itself, but mine is not, so I have to hold up the stopper.

At this point, you'll hear a short 'farting' noise as the Febco seals itself and directs the air to the 1" water outlet. If the farting noise doesn't go away after 2-3 seconds, then your compressor/piggyback setup might not be outputting enough airflow to make this work.

Once the Febco's flatulence is over, you should start seeing water coming out of the sprinklers in the running zone. After 5 or 10 seconds, your compressor will kick on and you'll notice the pressure has dropped substantially. It's a good idea to cut the airflow at this point by closing the top small valve, so you can let your compressor fill the tanks again.

At this point, it's fun game of open-blow-close-wait-repeat. Do this in each zone until you see mostly air/water vapor shooting out of all the heads. It's okay to leave a small bit of water in the system, but try to get out as much as you can before moving on to the next zone.

Finally, make sure to empty out the water in the line from your main water line to the Febco's downstream valve—hopefully there's a faucet somewhere at the bottom of that line so you can just dump it in a bucket.

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I was really after to learn more about adding capacity and stuck at issues with the piggy-back tank valves... this was really a helpful post. Thanks much and will stay tuned..


Thanks for posting this. I couldn't get the back-flow valve to close until I read your tip about holding it up and then opening the ball valve. You saved me the money I was about to spend to have someone come and do the job.

Excellent post. Saved the day for me. Like others, my air compressor (5HP, 10 Gallon) could not overcome the spring pressure in the Febco backpressure valve. Your pictures and explanation showed me exactly how to remove the bell housing and use a small screwdriver to get the pop up stopper to seal. I was then able to blow out all my stations as per your directions.

I looked at dozens of posts before finding yours. Thanks again for the great pictures and explanation.


You're quite welcome! I've had to do this for four years now, and I always end up coming back to this post because the process is just complicated enough I never remember the exact setup until I look at the pictures :)

I used a scuba tank (two actually) and rigged an old scuba regulator do push 70pai instead of normal 150+ and used your post to do all 10 zones myself. Thanks for this post. After a bad experience with a “sprinkler company” showing up and just started turning valves ( bypassed my softener and send untreated water through my house) I said no thanks and now I can do it myself. I also installed a RainMachine controller so I just stand in my yard and press next Zone on my phone. It was awesome. Thanks again !

Yeah, this year I bought a Rachio controller and it's so nice to be able to turn on and off zones when replacing a head, adjusting a nozzle, etc. I have almost all the heads replaced with Rain Bird 5000+ heads, and it's a lot easier to adjust everything so water gets exactly where I need it. Was annoying back when I had to turn on from garage, run out to head, see what it did, run back to garage, shut off the head, run back to sprinkler, adjust it, run back to garage...

Thank you very much for:
1) Creating this amazing article describing the winterization of a FEBCO 765-1.
2) Creating a blog for commenting to thank you without requiring registration.

I am a new owner of this anti-backflow valve. I thanked my luck and made it through last winter, but I am scared to try my luck again.

For feedback, my FEBCO had a C-Clip and a lock nut holding the bolt for the attachment of the bell. After removing the bell, I needed to replace the lock nut to keep the bolt from receding too far and hindering the anti-backflow valve from raising far enough to prevent air from escaping.

With your kind and helpful article, I will now feel a little more confident in the winterization of my sprinkler system.

Super fantastic Jeff! Thanks!! Everything spot on for what I needed and sequence of what to do with pics. Like the others, removing the bell cap and pulling the valve up before opening the petcock was key to not wasting air and immediately injecting into the zone. I've done it 2X in the past but, it's been 2 years so I forgot it all and remember struggling with getting the valve to seat. I use a pancake and it takes me two runs until I'm comfortable that all the water is out of my zones. It's going to hard freeze below 20F tonight so just in time. Perhaps one day I'll get and try a piggyback tank. You might also want to mention to leave all the valves outside (your #1, 2, 3, 4) at the Febco 1/2 open so it doesn't trap water inside to freeze in the valve.

Also a thank you! I had always been able to blow out my sprinklers without having to take off the cap. Then moved to a new home that had a brand new backflow. In guess the spring in that one was stronger and I couldn't figure out how to blow out the sprinklers. Finally came across your post. Thanks again!

I have no doubt that the method here worked for many people. Thank you for the efforts of putting this together.

I called Febco technical support and they told me two things. (1) The petcock only allows limited amount of air go through and it may not be enough air to blow the system (2) Should use the lower petcock not the top one as a preference.

When I bough my house, there is a connector on the lower petcock. It gives me the impression that this lower pet was used for something (like blowing out the sprinkler system).

Also, I have read a lot of online comments about not letting the compressed air go through the backflow system because it may damage the system.

I got all the hardware ready and am just waiting for the code weather to do the winterization. But I am a little concerned about all the conflicting information I am getting.

Any comments are greatly appreciated!

Just had issues getting air through my system and the heads to pop up. Found this article and the little trick of removing the bell and using a small screwdriver and it worked!! I used the top petcock fyi...

Yeah, just ran into the issue with the vacuum valve not sealing on my neighbors Febco, after blowing out mine yesterday with no issues, using my 20 gal 5 CFM compressor . We were about ready to give up on his, when he suggested cranking up the PSI. I only had it at 50, so set it to 90 and it worked fine. However, I will be printing your post out and putting this with my bag 'o compressor fittings, since the trick of pulling up on the stopper thingy might come in handy in the future. Thanks!

Thank you so much for figuring this out, documenting it, and sharing it!! Just went through your process and it worked great!

What is the purpose of the downstream petcock? Will it damage the system if the air hose is hooked up there instead?

What is the purpose of the downstream petcock? Will it damage the system if the air hose is hooked up there instead?

Excellent information! I added a piggyback tank to get a total 13 gallon capacity. I regulated pressure to 60 PSI. I have 9 zones that cover 25K square feet of lawn and landscaping. I was able to blow out a zone for about 30 seconds, then close the petcock and recharge the compressor for about 3 minutes. I did this for each zone, twice. I let the compressor rest a couple times during the process to let it cool down. The poppet or stopper that's mentioned in step #7 was a little finicky. If it didn't seal right away after I opened the petcock, I just pushed down on it slightly with a screwdriver and let it pop up quickly, then it would seal right away. All is good!

I stumbled across this post while trying to figure out the sprinkler blowout procedure as a new homeowner and recognized your name from the amazing YouTube videos you do. You do it all!

The tip about raising the stopper manually was invaluable. Mission accomplished. Thank you!

I just finished up using your write-up to winterize my house. It went like a charm! Funny to see your name pop up when looking for info about this. I always look forward to your content on YT and really appreciate the documentation on this.

I am so glad I came across your post. My issue was that when I connected my air compressor to the lower port (as suggested by my local sprinkler supply place), the air would just come out the top of the bell housing. It was your post that told me that this model (which is actually my neighbors) seems to have a higher spring force than mine (where 50-60psi works fine). I dialed my compressor output to about 80psi, and after minimal flatulence, was able to push the internals up against the spring and seal it. I was easy sailing from there. Thank You!

Just adding to the pile of appreciation for this post - thanks for this!
Coaxing the stopper up to get it to seal was a key piece of advice.

For those worried about the airflow damaging the backflow preventer internals, I could see that being a possibility if you're feeding the air through one of those little test valves since that would narrow the air stream and have it firing at high speed right into the preventer housing. I found an effective alternative that I think makes it way safer: I bought an air hose quick connect adapter for the outdoor spigot (sillcock) - it was like $7 on Amazon. That means the air is going right into that 1" water pipe and then directly through the backflow preventer, without the air stream ever narrowing into some kind of dangerous air laserbeam.

Again, thanks so much for keeping this post up and alive - it continues to help people!