check valve for salt water??

The problem with using small diameter PVC is that you're never going to get a ton of PSI from any pump, especially since you've got 6 outlets.
I ran a couple of calculations at http://www.reefcentral.com/calc/hlc2.php and even using 3/4" pipe the entire way, with 6 outlets, and an average of 4 - 90° bends (2 over the top + the tee), & a check valve, even using some of the strongest pumps available, the highest average per jet you're looking at is only ~170 PSI (which ain't a whole heck of a lot) - using a common pump like a MD12 won't even get you to 100 GPH per jet . . .
The best ways to get "good pressure" at the jets is to minimize friction (i.e. use larger diameter PVC) and to limit the number of overall jets. There just aren't many ways to force water, with good resulting pressure, through 3/4" PVC let alone 1/2" PVC . . .
Also, the sump return makes the system that much more inefficient. You lose a lot of energy only pumping the water from the sump to the tank. For that reason, a lot of saltwater guys (me included) run a pump dedicated to circulation which pumps water from the tank. This way, gravity negates the vast majority of head loss due to height and really only limits your pump output to the friction loss within your plumbing. You also don't need any sort of check valve of siphon break using a closed system. :thumb:

The Reef Central Calculator is a total system calculator for systems under pressure, hence the calculator output of total head loss in feet and in PSI. If it was a "drain" it wouldn't include the pump brand/type factored into the equation.

I'm sure, as the FlexPVC site states that 1/2" PVC can push 1200+ GPH. However, that particular chart is incomplete as it doesn't relate pump output to friction loss, thus it doesn't tell someone what their pump output is going to do in regards to the particular PVC diameter used, length of PVC, # of fittings, etc. So the maximum output of 1/2" PVC is ~1200 GPH . . . Is a MagDrive 18 or 24, which are rated for well over 1200 GPH going to be able to reach that maximum of 1200 GPH on 1/2" PVC. The answer in a resounding No.
And even though the threaded outputs on many pumps are 1/2" or 3/4", I don't think the intent is to use 1/2" or 3/4" PVC for the plumbing.

There also is a way to do the some of the calculations yourself using the information here (I use this more than the Reef Central Head Loss Calculator): http://reeflopumps.com/images/tips.pdf
Sequence (Reeflo) even goes as far as to give the ideal pipe diameters to minimize friction loss for certain GPH ratings (i.e. if you want to run 600 GPH the most efficiently, use 1" SCH 40 PVC).

prov356 said:

The Reef Central Calculator is a total system calculator for systems under pressure, hence the calculator output of total head loss in feet and in PSI. If it was a "drain" it wouldn't include the pump brand/type factored into the equation.

Click to expand...

You'/re right, my bad. I thought by your conclusion you'd used the other calculator. Should have looked.

Still not clear to me though how you can overcome the 3/4" bottleneck at the pump inlet and outlet just by using 1" pipe in the rest of the system. I'm moving 600gph (measured) through my 3/4" returns at 5' head with elbows, check valves, etc. That's the size outlet on the pump. Not trying to be argumentative, just understand.

Click to expand...

The inlet and outlets are already factored into the pump ratings - meaning that even though a pump has a 3/4" inlet/outlet, you don't have to worry about the "bottleneck" and the pump rating at 0' of head will still be the maximum GPH output. Does that make sense?

I've gone to a couple of manufacturing sites to showcase the thought behind the idea of using larger diameter plumbing.

I also like to think that the theory behind using larger diameter plumbing is like dragging your hand across sand paper (Your hand is the water, the sand paper is the PVC plumbing).
When you use larger diameter plumbing, it's akin to placing your hand casually on the sand paper and slowly moving it across the surface. Does it resist? Yes, but you are still comfortable and your hand is clearly unaffected.
When you use small diameter plumbing, it's like pushing down as hard as you can on the sand paper and ripping it across it as fast as you can. Does it resist? Yes, a lot more than the previous model, and your hand is now scratched up and possibly bloody (depends on what grit sand paper you were using :wink: ).
So, because the pressure in the pipe is less, there is less friction, thus less head loss. Subsequently, since you have reduced the head loss, the pump can perform at a level farther out on the pump's curve (i.e. a higher GPH) and because of that you'll get a higher PSI at the end of the line (i.e. UGJ nozzle).

Anyhow, here are the two answers from MagDrive's FAQ section and Sequence's (Reeflo) FAQ section . . .

Danner mfg. (MagDrive)
". . . [T]he friction or resistance added by the pipe and fittings the water must flow through is the Friction Head, which is added to the Static Head to get the Total Head. You can keep your Total Head as low as possible, maximizing the flow from your pump, by keeping the friction losses in the plumbing as low as possible, usually accomplished by using as large a diameter pipe and [the least amount of] fittings as possible.."

Sequence (Reeflo)
"There are two elements that cause pressure requirements in your system; vertical lift and
“FRICTION LOSSâ€

hey thanks guys for the info. after some considerations and a few talks and a lot of brainstorming i figured that if the flow rate was x through a 1" pipe (for a control) then by keeping the preassure the same (x) and reducing the pipe size the flow rate(x) would be the same but the pressure at the outlet would increase! similar to a preassure washer smaller hole more preassuer! so i decided to drop down to a 1/2" pipe up to the tank then at the top change over to the 3/4 (which was already there). in this fassion i did not reduce head preassure but increased the outlet preassure. the 3?4 pipe down to the bottem wouldnt matter much cause it takes a constant amout of force to push down so 1/2 3/4 or 1" would be the same. this worked! i ncreased the preassue to my jets noticably and the next problem was to adjust the jets so they didnt stir the sand up in the bottem. some tweaking solved this. of corse i am using a clear style flapper ckeck valve wich works great to keep the jets from siphoning my tank empty in the event of a power outage!

next i will be upgrading y sump from the 75 gal rated pre construct to a 10 gal aquarium sump custom made. i plan to incorperate solid and bio filtration ( of corse) as well as a fluidized sand filter with the possibility of a small refugium ( maybe). i have a working desigh but need to tweak it i abit. any ideas would be helpful

and thank agin all for the help!!!!