Important Question - are you using the MPR Reds (tree of 4 nozzles) or PGP Red nozzles (nozzle tree with 12 nozzles) and what model are your rotors exactly (PGP, PGP-Ultra, etc)? The MPR nozzles allow a matched precipitation rate for zones that have rotors in the same zone that have different rotation degrees (ex. 90 degree corner rotor and another 360 degree rotor operating on the same zone)
It is also important to know that all blue nozzles are precipitation rated for 180 degree of travel in that blue nozzle chart, so you have to do a little math if your rotors are not rotating 180 degrees. In your case, the 1.5 blue nozzle in a 90 degree rotation configuration will be .6 in/hr in a square “head to head” pattern (take the .3 in/hr precip rate in the chart rated for 180 degree rotation and double it to .6 because it is only travelling 90 degrees). The throw distance of the MPR red 90 and the 1.5 blue at 90 degrees does factor into the reason it is putting out less gpm for the MPR red but the precipitation rate will be very similar (.6 vs .62 in/hr)
So I am assuming if you are using MPR nozzles on PGP-Ultras. To properly retrofit your rotors with MPR nozzles, you need to:
- Determine Feet of Throw - First factor in the ft. of throw you need for head to head coverage (the number of feet it will take a rotor to spray the head of the other rotors in the zone). That will determine if you need MPR Red (25 ft.), MPR Green (30Ft), or MPR Beige (35 ft). Reds, greens and beige nozzles can be intermixed because they are MPR nozzles that have the same precipitation rate (assuming they are travelling the correct degrees of travel).
- Nozzle Selection based on rotation degrees - The next thing is how many degrees of rotation will your rotor be travelling. That is where you select the proper nozzle based on degrees of travel. (ex. MPR Red 180 will be used for a rotor that needs to throw water 25ft and will rotate 180 degrees back and forth).
- Ensure all rotors in the zone have a MPR nozzle installed based on their throw & rotation configuration. (you cannot mix MPR nozzles with blue nozzles).
One thing to note about the MPR nozzles is that the green and beige ones for 360 degree require fairly high GPM flowrate and some zones cannot handle or deliver that much water at that flow and pressure needed. This will be apparent if the old blue nozzles were delivering their water at their specified throw distance but the new ones are not throwing at their specified throwing distance anymore. Rotors usually work best at a minimum pressure of 30-35 psi. Anything lower will reduce the throw radius and have less uniform distribution of the water thrown in the stream radius.
Hope this helps shed some light on things.