Hi Steve R.
Actually, I really do not know anything about Nitrous systems.
But from the Holley Web site, the following:
"System Requirements
To supply the carburetor and the Pro Shot Fogger System use a fuel pump designed to operate between 5 and 10 psi with a flow rate of 0.1 gallons per hour per horsepower at 6 psi. Please note that most aftermarket pumps are rated under free flowing conditions. At 6 psi their flow rates may be greatly reduced. Check the manufacturer's specifications carefully or have the pump checked before you use it. "
0.1 gallons per hour per horsepower equates to .065 brake specific fuel consumption. Therefore, looking at Snake farmers 750hp motor with a 250 hp notrous add in you have 1000hp (Scary, at best!!!!) Therefore, 1000X.65=650 lbs per hour at peak output. Therefore a fuel flow requirement of 100 gallons per hour.
Still not a big flow rate. There are submersible pumps that will give you this number.
Snakefarmer,
I understand your wish to keep your current components and not throw away the dollars spent.
A ball or flapper check valve will not fix your problem as these are not a positive seal and you will lose prime. I would also be a bit concerned about just moving your pumps lower to reduce the head distance. I have never had good luck with that method.
Therefore, the only recommendation that I can make is to install a small pickup tank above the level of the existing pumps. Such as the Nitrous enrichment tank from
JAZ (click on fuel cells. I hate frames pages!!)or one of their other like products.
This could be feed by a in tank pump of proper size.
Sorry, I know this means more money, fabrication, and bleeding knuckles, but I know no other way to fix the problem with your existing fuel cell pickup system that would be reliable.