Presicion Drip Irrigation set up for 4x8 - 1 pump or 2

Two words -- Pressure Compensating (PC) Use pressure compensating emitters. These will require a 15psi or so to maintain consistency. Some can operate as low as 12psi, just read the specs and know which ones you chose. you can run 96 (totals 192gph or 3.2gpm from emitters) of these with a 5.5gpm 45psi pump. The psi on these pumps is adjustable 45-70ish... My psi ended up around 20psi from a similar pump and 96 2gph PC emitters. PSI is basically a currency. Each emitter, each tee, each 90-degree bend, the length of pipe/tubing etc all reduce PSI. You need 15-20psi remaining after all of that for it to operate properly. I bought 2 pumps before i understood that, lol. You want PSI not high GPM/GPH... though flow does need to be 'enough' too. Don't buy aquarium pumps! Example, not an endorsement: https://www.amazon.com/Tdrsuper-Pressure-Booster-Diaphragm-Bathroom/dp/B0BVLLFTP1 Tips and Misc... again, don't buy aquarium pumps, lol. low psi with high flow rate is not what you need or want. If you buy cheap no-brand emitters, expect at least 10% to fail. Buy the handled hole puncher for inserting the emitters directly into a 1/2" line. The one where you simply press something sharp into it is not as precise and doesn't cut as clean of holes. The plier-style hole punch is accurate and cuts very clean holes -- less chance of leaks and holds up better over time if you have to pull a defective emitter out to replace it. I did this with a couple and they were still water-tight. Avoid the 'adjustable' manifolds or emitters. All this does is result in you haveing ot adjust everything all the time in perpetuity. A little buildup causes slight pressure change? Need to adjust. NEed to shut one off because you chopped it down? Need to adjust all of them to callibrate it again and again and again and again, lol. Any slight change requires re-callibration to all adjustable emitters each time and it is no exaggeration. Add an inline pressure regulator before the line to the plants... make sure resulting psi is not too high. When i run fewer pots as i harvest plants, i make sure it doesn't operate over 20psi so i don't blow anything out. Consider an airvent, too. This will allow any airbubbles to escape pipe/tubing. There are special types of drip emitters that hold their water (minimum psi to push it out), which would mostly eliminate the need for an airvent, too. Read up on netafim's brochures (even if you choose a different brand) and it'll explain what i mean.. some can hold back a 3' column equivalent of water before they drip. This means they remain full of water after shutoff as opposed to emptying out, creating a bunch of in-line air that can make it spit when first turned back on. Mine don't retain the water, but also didn't have a problem with water spitting all over the place -- YMMV. I have an airvent but haven't bothered installing it. Shut-off valves for each pot. Avoid "spaghetti line" nonsense. The 1/4" tubes are trash. I have 1/2" looped around with a tee at each of my pots and 1/2" tube with 8 2gph emitters per 5-gallong pot with a shutoff valve inline with an endcap. I just coil it around and use a garden stake to hold it steady. In hindsight, i'd probably do the loop with 3/4" (my feed from pump is 3/4" ID) to 3-foot length of 1/2" tubs going to each pot and endcap. Loops are fine but you now need to get it around a plant before the plant gets large. I like simply wrapping the line around the plant and using a stake. But, even with 96 2gph emitters and 1/2" lines around grow area, it delivers enough water. It's probably up near the limit of 1/2" line. Think the math is around 208 gph? i can't recall.. there's different Inner Diameter options for "1/2" tubing. The 5.5gpm pump can probably handle a bit more than my 192gph worth of emitters, 12 tees, 3 90-degree bends and 30' of 1/2" tubing etc and a 15' 3/4" feeder...but the 1/2" line is probably the limiting factor in my setup. I'm probably only using "3.5-4gpm" of the 5.5 max, just a guess. You can see pictures of my setup growdiaries.com/diaries/232811-strawberry-cookies-og-r1-cherry-diesel-bbgs-ego-epg-ebg-grow-journal-by-001100010010011110/week/1366923 If you want to water more slowly, you can definitely use 1 or .5gph emitters and increase number of emitters proportionally. You can cover a SOG in a 4x8 with this size pump for sure. I went with what i thought was a step or 2 too far. I can water up to 12 5-gallon pots in about 3 minutes, if i recall. I dont want to be there supervising for long periods of time. You can definitely cover a lot more pots and water more slowly... just make sure enough emitters per pot to give an even distribution of water -- something i also tried to go a step or 2 too far rather than err on low side. Add in a controller and you can automate it. Orbit single or dual zone option is cheap. Even has option to add a pump relay switch and remote control and automated timers etc. I'm not a fan of depending on a solenoid valve to avoid a flood, but each to their own. I'm happy with push-button control. I flip a switch and it irrigates. Drain basin with float switch takes care of runoff. I walk away 3-4 minutes later.

presuming you mitigate any air in the line, the only real thing I'd be concerned about is your vertical rating on the pump...as that is likely the first thing you'll notice being deteriorated by age as far as two pumps or one? I mean, in a perfect world you'd be running off one with a validation system and a second as a backup on standby hydraulics =/= pneumatics, compression of liquids is different than air...long story short, throttles are your friend. I use stuff like Netafim Netbows/Halos...the ones I have deliver 4 drops of solution per second when not clogged up... That makes working back to an automation schedule really easy. Not all emitters are on the same quality level though.