Irricad

I am going through our designs and trying to utilize the products that we have in the field. I am limited to 8 to 10 inch yellowmine for our submain/mainline and 10 to 12 inch Emerald for Mainline also all of our manifold blocks use 4 inch layflat into T-Tape 7/8" 12" - 220. We use 3 and 4" nelson valves. We run our PRV at 12 PSI. I have a design that I get an error message when I run LP design: "Level: 5, ID: 5558, Name: IDE_DES_558 (Siz_lp) Message: Headloss too high:- fixed pipe sizes or PRV etc, too small"
When I hand calculate the head losses on our fields we are between 150 to 300Ft depending on where the pumps are located.
Is there a way that I can complete the design with these constraints?

Hi,
This message indicates that LP Design cannot not find a solution based on the limitations on the system. This could be size of enabled pipes in the database, the valve pressure setting, elevation change,the velocity limit, or fixed pipe sizes (i.e. some or all pipe has been manually sized). If there are computer sized pipe in the system, and many enabled sizes in the database, one option is to increase the velocity limit so that IRRICAD has some room to move in the selection process - this does not necessarily mean the pipes will be over your required velocity but will give you an answer. If the velocity is too great simply change the pipe for a larger one. Another option could be to run Velocity Design to find where the system is outside the required parameters - usually Velocity Design will find a solution (as the pipe is sized on flow only not on outlet requirements) and you can make changes afterwards to ensure the outlets recieve the required pressure.

I think my problem is on the fact that I have 2 water supplies running 2 different fields each block has 10 zones. I have tried a couple of different ways to tell the program which zones belong to the water supplies. The reason I suspect this is that I am receiving errors stating the pressures are to high on the tape blocks and or to low. When I run reports and pressure limits on the valves and tail ends of the tapes they are within the operating range of the tape 4 - 15 PSI is the operating range in the database and the pressures I receive on the valves are 11.8 and on the tail end of the tape is around 8 PSI. I tried Assigning each zone to an unique system flow, but each time I go back in there the changes I made are not saved. Under Supply 1 it is wanting to run zones -1 thru 20 and the same for supply 2. When I change that for Supply 1 to run zones -1-5 and -11-15 and Supply 2 to run -6-10 and -16-20 for some reason it does not save that setting.
It still shows pressure is greater or lower than allowable pressure on pipes. I checked my lay flat allowable pressure is 35 Psi and mainline allowable pressure is 160 psi I am not sure why it is saying the pressure is out of limits when they seem to be in the correct range.

You are doing the right thing with assigning which system flows are being supplied by each water supply. If the wrong system flow was assigned to a water supply it was not connected to you would be getting a different message. However, every time you go to the automated option of Assign Each Zone to a Unique System Flow IRRICAD will do exactly that - making sure each zone is on its own system flow. If you edit the management table, as you described, in order to view at a later time use Design|Assign Zone to System Flows (graphical management) or Design|Other Management Options|Assign System Flows to Zones (tablular option) - these options do not change the current assignments.
Note that because each water supply is supplying a different section (different zones) you do not need to set the water supply pressures, unless you only have a set amount of pressure to design the systems to at this stage. If you have set the pressure it may not be enough for the system you are designing.

I think I did the management correctly to separate out the water supply. After I complete this I still have pipes that are exceeding the pressure limits if I run the Velocity Design. When I run LP Design the headloss is to high. I did not set pressures at the water supply that should not be an issue. I may need to have a walk through on this design to understand why the pressures are out of limits. When I run show zone pressure limits on all valves they are within operating ranges.

Currently IRRICAD selects the most ecomnical size of pipe required. It does not select the pressure rating of the pipe as that is a designers decision. If the design is now working well after Velocity Design but the pipe pressures exceed the rating of the pipe, change the pipe(s) where required to a higher rating and analyse the changes. If the system pressure seems much higher than it should be check the headlosses through valves or Misc. hydraulic items.
For LP Design, given you can't widen the range of pipe sizes in this case, did you increase the velocity in order to achieve an answer? If pipes with a high velocity are selected increase the size, if possible, and analyse the changes.
You are welcome to send the design. Given the time zones for more timely support email your local support team at support@nelsonirrigation.com. Alternatively email Support@IRRICAD.com.

Yes I did increase the velocity to 8ft/sec, but it did not change. I still receive errors. I will send you the design with my database and maybe we can connect next week to discuss.

Thank you,

Robert

In this particular design the submain size had been pre-selected as the 4" layflat pipe. Selecting pipe automatically disables the "Computer Sized" option in the pipe dialog. Therefore LP Design could not run the algorithms to select any sizes hence the Message: "Headloss too high:- fixed pipe sizes or PRV etc, too small". If you know the pipe size you wish to use simply put it in the design and Analyze the system.

Note that if the pipes were originally specified as Computer Selected or "Computer Sized" was enabled LP Design would not have been able to find a solution for this design due to the valve pressure being set at 12 psi.

There was also a discrepancy in the Tape data in the Database used with this design. The tape had a maximum allowable pressure rating of 8psi but the control valve setting and tape pressure in IRRICAD was set to 12 psi (within the emitter minimum and maximum pressure range). This caused the "pipe pressure greater than allowable pressure" messages.

Thank you Jo for taking the time to explain this information to me. I understand now where to change pressures if one wants to run a specific pressure on a valve.