Well Pump issues.

Discussion in 'Irrigation' started by Jslimjeff, Jul 5, 2005.

  1. Jslimjeff

    Jslimjeff LawnSite Member
    Posts: 5

    Im a home owner who is going to install my second irrigation system. This one will be on sub. well 220 ft down. I know my well produces about 13GPM @ 45 PSI. If i size my heads to small and my pump runs 4 Minutes and off 30 seconds will this be a bad thing. Do I need to install a pump start relay to keep the pump on continuous when watering. This is the same pump for domestic water in the house.
    The recovery rate for the well is rated at 32GPM and I have verified that running at 11 GPM for 45 Min has not ran dry.
     
  2. Dirty Water

    Dirty Water LawnSite Fanatic
    Posts: 6,794

    If you size your heads too small, then just move up a nozzle size.

    You do not want a pump start relay.
     
  3. Wet_Boots

    Wet_Boots LawnSite Fanatic
    Posts: 48,034

    Size the system so that the pump is running continuously. As long as the well doesn't run dry, you will get the longest pump life with it running continuously during sprinkling.
     
  4. jerryrwm

    jerryrwm LawnSite Bronze Member
    Posts: 1,274

    Off for 30 seconds and then restarting every 4 minutes is what will damage the pump. That is what short cycling is. The motor comes under the most stress and strain everytime it starts. It puts stress on the bearings, and windings, and brushes, and will eventually lead to failure.

    Now, I still believe in Pump Start Relays, always have and always will. A running pump is a happy pump. The PSR will turn the pump on when needed, keep it on during the cycle, and shut it off when finished. No short cycling, no pressure fluctuations, no head fluctuation, Nada. It also helps protect the pump motor.

    Now, if you are able to balance the system so that it is operating at the exact same flow and the exact same pressure, then a pressure switch would be fine I guess. But how many systems are that close? If you design the system for say 11 gpm @ 40 psi, and you have a zone that is 9 gpm, the pump will increase the pressure output. And if you have your pressure switch set at 30-50 the pump will supply more pressure sooner and shut down the pump as it is supposed to. But it will be back on in just a few seconds because the drawdown in the pressure tank is quickly used up and the pump is back on.

    I would rather use a PSR and deal with pressure requirements on a zone by zone basis.

    Just my thoughts,

    Jerry R

    PS - Not to steal your thread, but I am wondering how big a problem it is that wells go dry. By that I mean, how many wells do go dry in a particular area? Is it a common occurance? What is the cause? In 25 years of irrigation I have never seen a well go dry because of irrigation pumping. They may go dry because the water table changes in a drought situation. The recovery rate may be slower than the demand rate of the irrigation system because the water sand is tight and may be a shale rather than sand. That is not a dry well. It is an poor well. The recovery rate is going to be extremely slow.
    Maybe the well casing is not perforated enough, or the pump is barely in the water strata. That is a well that was not installed for irrigation, but rather for domestic use. More screen on the casing and setting the pump lower will help that situation immensely. But that will be costly.
    Another option for poor wells or undersized wells is a storage tank (1500 gals or bigger) and a centrifugal pump. Let the well pump free-fill the tank with a float valve setup and pump from the storage tank.
     
  5. SWD

    SWD LawnSite Senior Member
    Posts: 989

    Don't horse around with all of the "balancing" of the nozzles. Design in a 10 to 15% additional use factor for a hose bib then install a cycle stop valve.
    Look at cycle stop valves on the internet-and follow ALL of the installation directions. These valves aren't cheap, but work extremely well.
     
  6. Wet_Boots

    Wet_Boots LawnSite Fanatic
    Posts: 48,034

    What the hell is so difficult about evaluating a well's performance, and configuring the system to fit? When I work with a home supplied with well water, I have no opportunity to add relays or anything else that can control the pump's operation. I do get to tweak the pressure switch, and often do, to improve the system performance, and in doing so, sometimes, achieve a balance point that allows continuous running.

    As for wells going dry, it is not unheard of in rocky strata, where the inflow can be skimpy. I see it all too often. Since some sprinkler controllers now allow long delays between zones, it's obvious the manufacturers are aware of the possibility.
     
  7. jerryrwm

    jerryrwm LawnSite Bronze Member
    Posts: 1,274

    The evaluation of a well's performance is the easy part. Running a flow test, checking pump performance curves and well driller's logs will tell you what the well is capable of doing.

    Getting all the zones to operate at the same flow and pressure is the hard part. Getting a 13 GPM zone of spray heads balanced with a 13 GPM rotor zone is difficult to balance since the optimum pressure for spray heads is 30 psi and for rotor heads is 40-45 psi. (at the last head) Tweaking the pressure switch allows you to increase the cut-out pressure to keep the pump running, and increasing the differential will also help keep the pump running.

    But you still need to control the cycling. Most residential systems use a pressure tank set-up that works fine for low flows demanded in a home - usually 5 - 7 GPM. A larger pressure tank, or additional pressure tanks will help with this problem, giving more drawdown capacity. Or a pump start relay which is wired to the pump motor load side (T1 & T2 terminals) will keep the pump running during demand is nothing more than running two wires (common and PSR wire) to the well head which activates a 24v coil. Nearly every controller on the market has a pump start terminal so it is a simple hook-up. The controller then operates the pump for irrigation and the pressure switch operates the pump during household use.

    As for wells going dry, we are talking semantics. Tight water strata often results in a slow recovery rate, and the pump is only set deep enough to supply water for the residential use. When an irrigation system is added, the recovery rate is exceeded. The well is not dry, per se, but rather it is slow. Many times this can be resolved by setting the pump deeper in the well and increasing the casing screen area. This will increase the drawdown to static water level. This can be expensive especially on older wells. A larger pump may be required to overcome the additional head, the casing may need to be perforated downhole, it may need to be acidified to breakdown calcium build-up, etc.

    If you are lucky enough to be consulted beforehand on a new construction project, the well can be drilled to accomodate irrigation. Oftentimes an additional 20' in depth will make all the difference in the world.

    Also controller programming will help with a tight well. Controllers with delays between zones is one way. Or using an oversized controller and using every other station as a delay period is another. Also utilizing the multiple programs and watering several stations on prog A, then setting a later start time on prog B, and another on prog C will accomplish the same thing. Or you can even run the system to water over a two or three day period, watering part of the area on one day, another the next, and if needed another the following day. Then starting over. That way the entire yard is watered on a two or three day cycle.

    Jerry
     
  8. Wet_Boots

    Wet_Boots LawnSite Fanatic
    Posts: 48,034

    For the sake of semantics, I use 'running dry' as meaning the water level in the well has dropped to the level of the pump, at which point the pump is no longer capable of supplying water. Modern rotor sprinklers, with interchangeable nozzles, make it pretty easy to tweak a system to match a well's performance, and assure continuous pump operation. Mist head zones are a bit trickier, and it would pay to know for a certainty, what the well is supplying, if you envision mist head zones. I would consider it a matter of sloppy design work if anything but pressure switch tweaking was needed for proper sprinkler operation.

    If the purpose of adding a control relay is to force constant operation, that addition would defeat the protection that the pressure switch provides, for the pressure tank and supply pipe. Make a proper selection of sprinkler heads, and everything else takes care of itself.
     
  9. jerryrwm

    jerryrwm LawnSite Bronze Member
    Posts: 1,274

    Matching rotor head nozzles and tweaking the pressure switch is fine if that is all that is being used on the system and there are no elevation changes in the system. The pressure requirements are the same for all the heads and it is fairly simple to set up. But if you are using spray heads, rotor heads, and drip zones, all of which can be found on a 'non-sloppy designed' system, then the pressure switch tweaking is useless. With a range of pressure requirements of between 15 psi and 45-50 psi, the pressure switch is adjusted to what pressure? One way or the other there will be short cycling or over pressurizing. And if there are changes in elevation between zones of say 15' - 20' or more, then the pressure requirements are also different. Many variables that a pressure switch tweaking alone can't handle properly.

    It is also a simple matter to install a flow switch downstream of the pump that will shut down the system after a timed delay in the event of valve failure. Relying on a pressure switch as a failsafe shut-off device is kinda risky as pressure switches have a tendancy of failing also. Contacts become stuck, springs weaken, etc. So a combination of pressure switch, flow switch, and pressure relief valve would afford the best protection in the worst-case scenario.

    Suffice it to say, we all will use whatever method of supply water to our irrigation systems that work the best for each of us. We will all design head spacing, pipe sizing, wire sizing, etc, that works for us. We will use the brand of equipment, the type of piping, and the installation equipment that works best for us. And regardless of how 'sloppy' our design may appear to be, it is really of concern to the installer and the end user as long as industry standards and guidelines and local codes are followed. Pumps are the same thing. I rely heavily on the pump manufacturer, the pump supplier, and the well drillers to get the proper information, and act accordingly. It prevents a lot of headaches and lost dollars down the road.

    Jerry
     
  10. Wet_Boots

    Wet_Boots LawnSite Fanatic
    Posts: 48,034

    :p Uhh, hello? Ever heard of valves with flow controls and pressure regulation? Most of the well water systems I encounter are not to be modified, outside of some pressure switch tweaking. Not my turf, and I gladly relinquish the responsibility to the well and pump guys. So with a "This is your water supply - deal with it" situation, I have to make the sprinklers work with what I have. Drip can be the real annoyance here, if it isn't consuming water at a rate to match the well's output. {Makes me wonder how many small drip zones are still being installed, the kind that run less than half a gallon per minute, and run for several hours, often overlapping the regular sprinkler watering} On well water, sometimes sandy, I can be happy to never have anything to do with drip.
     

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