defying physics?

Discussion in 'Homeowner Assistance Forum' started by SGC canal water, Jul 7, 2019.

  1. SGC canal water

    SGC canal water LawnSite Member
    Messages: 8

    We have a 4 zone lawn irrigation system with the water intake coming from the canal.
    The intake pipe has a check valve and sits 18 inches deep in the water. That places the intake anywhere from 3-4 feet lower than any of the sprinkler heads. The length of pipe in the water is approximately 20 feet running along the edge of the seawall.
    The problem: The screened intake and at times 15 feet of the pipe has been found to be "floating" on top of the water. This might repeat every 10-14 days, even though the system has been running without problems in all 4 zones the day prior. This started 8 weeks ago in the system which has been in place for over 4.5 years.
    The company said that the problem was the Aquasleeve material on the intake pipe reducing pressure, or the check valve must be failing- somehow allowing the water to drain out of the system, hence the intake pipe eventually filling with air and floating to the surface. 4 weeks ago a small leak at the elbow where the pipe rises from the water at the level of the seawall was repaired. At that time the check valve was found to be OK and a new piece of Aqua Sleeve was placed (it gets brushed at least once each week). Yesterday the pipe was up on the surface again.
    I said that the water would seek its own level and that even with a "leak" in the system, the water would not passively be displaced by the air, especially 2 feet under water.
    HELP, please.
     
  2. Andrew H

    Andrew H LawnSite Silver Member
    Messages: 2,627

    All the unions are tight? Did you try replacing the one way valve?
     
  3. OP
    OP
    SGC canal water

    SGC canal water LawnSite Member
    Messages: 8

    Thanks for response.
    Any unions I can get to seem to be OK, but I cannot rule out another seam leak somewhere at a PVC joint. I found the first one by running water from the garden hose into the "spigot outlet" at the pump. It was a barely noticeable dribble. Rain makes any such eval impossible today.
    Do you mean the "check valve"? - it was replaced 2 years ago after an ivasion of some small clam-like creatures in the canal system which destroyed many intakes in the neighborhood. (hence the use of the Aqua Sleeve). It seemed to be working properly when the guys looked at it 3 weeks ago.
    Even so, how would the air get 2 feet below the water level? Is there any way that air would essentially get forced backwards?
    Why would the problem be so intermittent? All was well Friday night, then the pipe was seen to be floating the next afternoon.
     
  4. Outlawn

    Outlawn LawnSite Bronze Member
    Messages: 1,154

    If the pipe is floating on the surface, then the air is not 2’ underwater, right? Not being a smart@$$. I see what you’re saying with the pipe floating up but it’s probably not that the air is getting under the water line; the pipe itself is moving as the air comes in and the air is able to move in longways on the pipe, floating more up, rather than floating vertically like a bobber.

    It is probably, as you and the previous poster implied, that there is a leak at either the check valve, in a fitting, or in the pipe.

    First thing I would check is to ensure that the check valve is oriented so the flapper moves vertically. Also, is there a lot of moss or sediment or anything? A little bit of debris on the check valve could cause it to not close all the way and have a slow drain down.
     
    hort101 likes this.
  5. Andrew H

    Andrew H LawnSite Silver Member
    Messages: 2,627

    Have you thought about connecting an air compressor to it and see if it
    Bubbles or you hear an air leak?
     
    GrassManKzoo, Outlawn and hort101 like this.
  6. OP
    OP
    SGC canal water

    SGC canal water LawnSite Member
    Messages: 8

    I appreciate your thoughts.
    Just to clarify... The guys who installed and provide service to my system came out in mid June when the problem first cropped up. They insisted I did not have a leak and blamed the Aqua Sleeve material which they claimed was reducing the water intake pressure. When we put the system under pressure by the municipal water, they then saw the very tiny dribble leak at the PVC elbow at the top of the seawall which I had told them about. After they tested the check valve, the PVC pipe leak area was replaced, and putting on a new piece of sleeve material to humor them, the system worked for 3 weeks or so without any problems.
    The layout of the system... From the pump, the PVC pipe runs underground until the sea wall where it comes out of the ground. There are approx 30 inches of vertical pipe from the top of the seawall going into the water, where there are 20+ feet of PVC pipe under at least 18-24 inches water running along the seawall. The pipe runs horizontally - so the check valve (which I believe is the standard spring loaded type from Home Depot) is horizontally positioned and does not have a vertical movement. The check valve is next to the intake end piece. The intake end, covered by the Aqua Sleeve which keeps out any and all particles, is at the lowest point of the entire line.
    When I need to "fix" the floating pipe, I simply run the pump, push the intake end under water and within 30 seconds, it "sinks" back into position. It may take 10-14 days for it to "float" back to the surface. The system runs 6 days of the week, so it would seem that the water is not routinely completely draining out.
    Even if the check valve is not completely closing, how would the water passively flow out below the water level to be replaced by air? Even if there is an airleak (which I will search for with a hose once the rain stops), the pipe should stay under water, unless the air is somehow being forced in a reverse direction from the pump and back down the intake pipe...
    Clearly, the air is not coming in from under the water level.
    I don't have an air compressor. It's certainly cheap enough to get a new check valve, and even replace the entire run of PVC pipe which goes from the seawall and underwater. I would still like to understand what is going on to ensure there is not some other issue which is creating this phenomena that seems to defy everything I ever learned in science class.
    Thanks and please le tme know your thoughts.
     
    Outlawn likes this.
  7. Andrew H

    Andrew H LawnSite Silver Member
    Messages: 2,627

    The way air would be below the water line is simple. The discharge is higher than the intake (which is why their is a check valve) Water can push air just as air can push water. Occasionally there will be a master valve right at the pump to help prevent this backflow but that’s not always the case.
    Do you have a master valve?
     
  8. OP
    OP
    SGC canal water

    SGC canal water LawnSite Member
    Messages: 8

    Andrew- I just took a look and do not see any additional valve at the pump area.
    I understand that water can displace air, but air floats to the top of water, so what is providing the force for the air to "push" and displace the water? I understand that the air might get as far along the pipe until it reaches the water level of the canal which is supposed to be the lowest point to which the water would passively drain, but not how it gets any deeper than that; unless something is essentially increasing the air pressure. I would like to be watching the intake pipe at just the moment when this phenomena is taking place....
    If I were to put an air compressor line onto the pump, wouldn't the air preferentially go out the sprinkler heads? Would I need to have the municipal water input opened in order to get the air to go back down the canal intake pipe hoping to see/hear some air leak? What if the leak is in the underground section of the pipe between the pump and the seawall?
    Thanks again!
     
  9. Andrew H

    Andrew H LawnSite Silver Member
    Messages: 2,627

    If the head is great enough, which it probably is, water will easily force air below the water line and air will be trapped thus causing the line to float.
    Chances are the system has valves somewhere unless you turn the pump on only when you want to water. The air will only go as far as the valves.
    Once you fill the system with air, yes you will need to re prime the pump
     
    hort101 likes this.
  10. Andrew H

    Andrew H LawnSite Silver Member
    Messages: 2,627

    Correction, the air will stop when it hits water or a valve
     

Share This Page