I have a design with a 75 metre variation in elevation. not all in one block but spread out over a range of blocks. The most a single bloc falls is about 15 metres. The zone design fits into the pressure parameters quite well (PC design)in velocity design and having multiple lateral and submain sizes.
My problem is in the mainline design. Error DES_498, Negative Pressure keeps coming up. I have adjusted my D/S valve pressures in Design Config by the negative amount shown but so far have been unsuccessful in balancing my pressures. Any thoughts?
Negative mainline pressures
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Jim Phillips
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jovivier
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Re: Negative mainline pressures
Without viewing the design it is a little hard to tell.
Possibilities are:-
- An error in the elevations - have you viewed the 3D DEM View or run Design|Calculate Elevation Errors?
- Have you set the water supply pressure? If so, this could be too low for the currently selected pipe sizes. Check in the Design Full report for high headlosses and make manual changes.
- If you are using Velocity Design remember it doesn't know about the pressures you are trying to achieve at the valves only what size pipe to push that amount of water through. Velocity design usually provides an answer even if it shows where the problem areas are - like negative pressures. However, it is best to use LP Design if possible (you can now turn off trading capital costs in Design|Design Parameters|Economic Parameters if you wish). If LP has trouble selecting pipe sizes (and you have a good range of suitable pipes enabled for mainline in the database) you can increase the velocity limit so that LP Design can find a solution. If the velocity in the design ends up being above what you would like increase the pipe sizes manually. Note LP Design can't be used in looped / ringmained systems or when a system has multiple water supplies.
Note if using LP or Velocity design make sure there are 'computer sized' pipes in the design to be sized.
Possibilities are:-
- An error in the elevations - have you viewed the 3D DEM View or run Design|Calculate Elevation Errors?
- Have you set the water supply pressure? If so, this could be too low for the currently selected pipe sizes. Check in the Design Full report for high headlosses and make manual changes.
- If you are using Velocity Design remember it doesn't know about the pressures you are trying to achieve at the valves only what size pipe to push that amount of water through. Velocity design usually provides an answer even if it shows where the problem areas are - like negative pressures. However, it is best to use LP Design if possible (you can now turn off trading capital costs in Design|Design Parameters|Economic Parameters if you wish). If LP has trouble selecting pipe sizes (and you have a good range of suitable pipes enabled for mainline in the database) you can increase the velocity limit so that LP Design can find a solution. If the velocity in the design ends up being above what you would like increase the pipe sizes manually. Note LP Design can't be used in looped / ringmained systems or when a system has multiple water supplies.
Note if using LP or Velocity design make sure there are 'computer sized' pipes in the design to be sized.