SPRINKLER TALK FORUM - You Got Questions, We've Got Answers

Hi; Since no one has answered you, I will try:

First some questions, Please excuse my answers if they ar way off base, but I obviouisly can not picture your situation

What type of backflow apparatus? Assuming you are worried about trapped water, I am assuming a DCA or RPZ? both have stop cocks for flushing and testing, and can be used as air vents to drain the apparatus. If you ae worried about the last bit of water, a house hold compressor is adequate for blowing out the remainder assuming you have closed the supply side ball valve, and flush thru the distal ball valve AFTER YOU HAVE ALREADY DRAINED THE REST OF THE SYSTEM. Please note, a home compressor cannot supply enough volume of air to blow out a whole zone. (again I know you know this, but others reading may not) If they are connected correctly, isolation and drainage should be easy. How do you prevent the water from POC to the BFA from freezing in the supply pipe? If it doesn't freeze there, will it freeze the BFA? Drainage is especially easy if the BFA is elevated (as all RPZ's or PVB's need to be), or if a DCA, if you are draining the distal fields (as you should). I am assuming you are draining the distal main and laterals.

WHY? Seems like if it is near your POC in a residential area,you ae making it easier for thieves (here scrap thieves lift anything copper or brass). This may not be applicable to your situation, but others read these threads).

Now, the answer: Seems like more work to me. BUT, the use of two unions on either side of the BFA, simply unscrew them and lift it out. Brass of course.

Jeff

Two additions to prior post.

RPZ's may not bwe drained as easily as I implied, since there are several different designs,

Water expands 112% when frozen, no matter how cold it gets. So every drop does not need to be removed from back flow devices.

Jeff

I will add this.

A Home comp will blow out a sprinkler sys no problem .This is false info. In fact you do not even need a lot of PSI to do it.

Lastly, I have installed unoins on all my systems to remove backflow for winter. Prevents issues in winter etc.

Quoted from "debo"

I will add this.

A Home comp will blow out a sprinkler sys no problem .This is false info. In fact you do not even need a lot of PSI to do it.

Lastly, I have installed unoins on all my systems to remove backflow for winter. Prevents issues in winter etc.

From what I understand, the reason it's usually stated that a typical home compressor can not blow out a sprinkler system isn't because of pressure but because of lack of volume.

After all, even those little compressors that run off your cigarette lighter put out over 150 to 300 psi. But you are NOT going to blow out an irrigation system with one of those compressors.

Whether or not a compressor can properly blow out ALL the water from your irrigation system depends upon the CFM or CFPM (cubic feet per minute). Typical home compressors don't have the needed CFM rating to get all the water out of an irriagaion system designed for something like 10 gpm of water flow. With too weak (in CFM rating) of a compressor, what you might do is have enough air to blow out the water to the first sprinkler head, but all the water will remain in the system after that. Or more likely, you will only blow the air out of the top half of the pipes and water will remain in the bottom half of the pipes.

Now I do NOT have enough knowledge to tell you what sort of CFM rating is required to blow out an irrigation system, but I do understand the concept.

I agree but I have a little typical home owner compressor and it is 11.3 sfcm at 40 psi..It is a small Ingersoll Rand 60-Gallon

If someone thinks for one minute to blow out a system with a cigarette lighter, umm, they should dial 911 clown! LOL

Then again you do not need to blow out the complete line since the water will not expand this much. If you get below 50% you are fine. I know people that doe zero and are fine with no CV..Sometimes I wonder if the blowouts are a scam...

Quoted from "HooKooDooKu"

The only source I know of with detailed information about blowouts it what I've read at http://www.irrigationtutorials.com/winter.htm.

According to the irrigation engineer that wrote these web pages (to help the DIY home owner) you need a MINIMUM of 20 sfcm to blow out a SMALL irrigation system (like 3/4" PVC). Even at that size, the author claims "And that is so small that it is not going to do a very good job!".

These are not my words... these are the words of an irrigation engineer.

I agree with what you read, but it is lacking in some important things. #1 is some XXscfm at WHAT PSI?
#2, is you can blow out a 1 acre system with a comp 1/2 the scfm as mine. It is done today and years back. I works on 1" poly and 1 1/4" poly as again today.

In you look at thermal exp of water etc, you do not need to remove all the water. If <50% of water in pipe you are fine. In fact if you have too large a comp you will run rotors dry and burn them out. You cannot have a small comp and expect it too work but other comps will and do work.

I have read this years ago and is a nice read but some issues are a little scewed. Like "removing the backflow preventer.." Are you for real? No on does that. You can also have 50% of the local biz blow via the test cocks too which some say no.. or "R-11 fiberglass " LMAO..

Again good read but that with a huge grain of salt, large then a horse. Again I nice read but app engs are not in the field.

Quoted from "debo"

Again good read but that with a huge grain of salt, large then a horse. Again I nice read but app engs are not in the field.

True, but I understand where he is coming from. He is trying to explain things in such a way to cover all the bases and take into consideration all the little things that many people may not think of.

As an example, your idea of blowing out enough water so that >50% is gone will NEVER fly with this guy. The reason is because that logic is ONLY going to work if your pipes are perfectly level. I seriously doubt all your irrigation pipes are perfectly level. If they are not, then what will happen is that water will seek the lowest point. So if in a long run of pipe, the pipe forms a slightest of "U" shapes (say where the center section of the pipe is just 1" lower than the ends) and you only blow out 50% of the water, the water that is left will collect at the bottom of that "U" and completely fill the pipe at that point. When that section of water begins to freeze, you will bust the pipe at or near the bottom of that "U". After all, the parts closest to the surface are likely to freeze first most likely forming a plug to the water at the bottom of the "U" with no were for that water that freezes last to expand to.

You might think of it this way. When this guy tries to tell you how to do something, he's telling you how to do it so that it will work 100% of the time. But if start taking short cuts, you significantly increase the risk of screwing something up or breaking something. Now most likely the short cuts you take will work. But eventually, there will be that person for who the short cut jumps up and bits them in the ... well you get the point.

PVB backflows in general don't need to be removed if you've winterized the system properly. personally, I like to remove RPZ backflows for customers for the winter. They have a high probability of not draining, and freezing and the replacement value alone dicates common sense. They are easily removed with two unions and stored inside. As for the PVB, you can either add unions, purchase a new backflow that comes with unions now (check out the Febco model). or, remove the top bell shaped cover and unthread the bonnet and popit as these are common stress parts over the winter. Just make sure you "regrease" the threads when you reinstall it. If you have a "blow out port" or "stop cock" below the backflow, keep it open for the winter.. this will allow any excess water to drain (however a proper winterization would leave none) and in the event someone recharges the sprinkler system by accident over the winter, the water will flow out before entering the backflow. As far as removing the entire thing, I don't feel that's neccessary.

FYI: I winterize my systems with 185 CFM towable compressors. I am able to open multi zones in one winterization. Watch the last head on the line for complete removal of water. Most Poly hose is rated to 100PSI, so I keep my compressors running around 90 to 95 PSI. Any more and you could potentially blow pipe apart.

Quoted from "OSLSprinkler"

PVB backflows in general don't need to be removed if you've winterized the system properly. personally, I like to remove RPZ backflows for customers for the winter. They have a high probability of not draining, and freezing and the replacement value alone dicates common sense. They are easily removed with two unions and stored inside. As for the PVB, you can either add unions, purchase a new backflow that comes with unions now (check out the Febco model). or, remove the top bell shaped cover and unthread the bonnet and popit as these are common stress parts over the winter. Just make sure you "regrease" the threads when you reinstall it. If you have a "blow out port" or "stop cock" below the backflow, keep it open for the winter.. this will allow any excess water to drain (however a proper winterization would leave none) and in the event someone recharges the sprinkler system by accident over the winter, the water will flow out before entering the backflow. As far as removing the entire thing, I don't feel that's neccessary.

FYI: I winterize my systems with 185 CFM towable compressors. I am able to open multi zones in one winterization. Watch the last head on the line for complete removal of water. Most Poly hose is rated to 100PSI, so I keep my compressors running around 90 to 95 PSI. Any more and you could potentially blow pipe apart.

I agree, I have installed unions before and after PVB but most users do not do it (winterize) anyways. It is an ease of replacement and removal for winters etc. Then again most installers will not do this since it is an easy call back for $200+ backflow.

If you read Febco you are not to leave 100% open on the test cocks. You are to leave on a 45 DEG.

I also agree a large comp will blow out multi zones at one time but if you read Hunter IND you are not to use PSI greater then 40 PSI for the reason I noted prior.