Most home construction with outside hose bib's have Hose Bib Anti Siphon valves by code for anything that's connected to the hose bib. If one is not installed it's certainly a good precaution.
I believe it would simply be a matter of connecting your existing system to the new one using a fitting similar to the one depicted in the attached picture. Your existing system, I presume, would have a standard plumbing fitting to attach to the 3/4" MPT side, the Orbit system would attach to the Blu-Lock side like all their other fittings.
It is as many as you want.... generally down to water pressure/supply but no more than 6 per line
Your question is not answerable as presented.A picture of the Orbit kit accompanies this e-mail and shows all the parts that are included. It would be helpful if you could identify which fitting you need from that picture. Otherwise I can only guess which part you need. When you say 1/2 inch hose connector fitting leads me to think maybe you want a fitting that will allow you to screw your hose directly to one of the zone fittings instead of using the timer. Yet 2 of those fittings are included in the kit. Is one broken? Other fittings include the underground fittings of 90 degree elbows, unions and drain fittings. For these it should be noted, the tubing is not a true 1/2 diameter. Perhaps if I could understand precisely what you want to change or repair, I might have a better idea of how to direct you. I would also suggest, if you have the owners manual to possibly identify the part you need from the manual. Finally, it may be necessary to contact Orbit directly. Contact information for Orbit is available in the manual and they're customer service is fabulous. Another possibility would be to take your broken or defective part to your local Home Depot store to see if they can match a part from their stock.
I'm not a great mathematician but I can see you've over thought this (nothing personal). There is a formula for determining square footage in a radius but unfortunately it doesn't apply here very well. The first reason is that Orbit recommends that you lay out your system so that each head overlaps each corresponding head to the next location. Incidentally, each head can be adjusted to a full 360 degree radius. This sounds like you might be watering each spot twice as much. However, when you look at the diagram of a layout plan, gives a much better idea of why it's laid out this way. When trying to lay out the heads so each just reaches to the next, there will always be a bare spot that doesn't get water at all at the center of the square. And this all has to do with the radius (or sweep). For instance, if I have (for example) a 60 x 60 square (360 sq ft) and 4 heads, each spraying about 25ft, (think this is where you got the 25 from), I will overlap the corresponding heads which each would be adjusted for a 180 degree sweep (corner to corner). However, I will end up without water at the center, of approximately 10 ft radius. I would need a fifth head in the center to spray 360 degree's to cover what the corner heads missed. Keep in mind that a head spraying a 360 ft radius will take about twice as long to rotate so I will still only apply about 1/4 as much water as a head spraying 180 degrees because my 180 heads are providing twice as much at any point that overlaps while only rotating 1/2 as far. All of this is contingent on the actual size of the area you have, your water pressure and any obstacles. This is why a plan is imperative and water pressure optimal. I am providing you 2 sites to help. One is the formula for calculating radius (into sq ft) and the other is from Orbit on planning and laying out your system for best performance and results. https://homeguides.sfgate.com/convert-diameter-square-footage-8735.html https://www.orbitonline.com/how-to-layout-an-underground-irrigation-system/
It all depends on your water pressure. I used three heads per Zone and had adequate pressure. I doubt more than three would have given me enough pressure, possibly starting the water at the center of a zone and going outward may help with going up to 6 heads.
I rented a small trencher from my local Ace Hardware. 8” deep is required for the sprinkler heads.
Minimum operating pressure is 25 PSI per zone or 6 heads. Optimum operating pressure is 35 PSI
NO. Disconnect hoses, remove the timer and drain any water and remove the batteries. Underground lines should be blown out with compressed air and an environmentally safe anti freeze should be poured into the system. Essentially this system needs to winterized the same as any professionally installed system to avoid deep freeze which could result in broken heads and tubing connections.
Yes. If this ground pump is also responsible for potable water, you should install an appropriate back flow prevention valve.