Zone Pressure Tolerance

[Samantha]

Hi ya'll,


I read the description of what the Tolerance % Above/Below is:

Tolerance % Above:
Enter the “Zone Pressure Tolerance % Above”. This indicates the upper limit of the pressure window that the tape is to operate in.

Tolerance % Below:
Enter the lower limit of the pressure window the tape is to operate in (“Zone Pressure Tolerance % Below”).

My question is, what is an accurate way to get this number? Any help is much appreciated.

Thanks,
Samantha

[jovivier]

Hi Samantha,

Essentially the tolerances are a designers decision based on the pressure ranges or flow ranges (for outlets) you wish to allow in your design.

Regards,

Jo

[Harvie]

Hi Sam.
It's good to see you giving IrriCAD a good flex.
Australian standards for emitter flow variation is a maximum of 10%. A good designer will usually design for less than this depending on how critical the job is. 10% or less is easily achieved with quality pressure compensating emitters. But quality non-compensating emitters with an x value (emitter exponent) of around 0.5 will give you a flow variation of 10%, if the pressure variation is 20%.
For example: If you decide that as a good designer you will aim for a flow variation of 6% (3% above and 3% below your desired flow rate), then you should set your pressure tolerance % for 12% total. (6% up and 6% down).
Remember that this is only for a non-compensating quality emitter with an x value of 0.5.
Cheers
JH

[aquacg]

Hi, does this mean the zone pressure tolerance is based only on the settings in the specific tape used or can I set the pressure on a zone valve also? Should the zone valve pressure setting be set at the same default inlet pressure of the tape used? Thanks.

[jovivier]

Velocity Design only sizes pipe on flow and does not consider required outlet pressures. Therefore the tolerances are ignored for the pipe selection process but are used in determining the valve pressure (if not specified) and the construction of any warning messages.
During LP Design IRRICAD selects pipe sizes to achieve outlet pressures within the required tolerance settings.
However in Design|Zone Design Configuration you can:-
- Set a valve pressure. Usually set above the maximum allowable outlet pressure but this is a function of elevation, length of pipe before the first emitter/lateral, etc. Easy to change if the pressure is too much or too little and re-run Design.
- Set specific minimum and maximum outlet pressures for this particular design and enable "Don't Use Database Envelope". Very useful if the tolerances in the database are normally used but not in this particular case.