c)TWO-PIPE GRAVITY SYSTEM (not recommended) - Used when a fuel oil storage tank is located above an oil burner fuel pump. See Figure 15. A vertical distance from top of the tank to center line of the pump (Dimension ‘H’) over 8 feet will result in a pump inlet pressure in excess of the 3-psi limit in NFPA-31. This type of system should be converted to a one-pipe gravity system, as doing so will result in lower inlet line flow and longer filter life.
d)TWO-PIPE LIFT SYSTEM - used when a fuel oil storage tank is located below an oil burner fuel pump suction port. See Figure 16. The vertical distance from bottom of the tank to center line of the pump (Dimension ‘H’) must not exceed that shown in the pump manufacturer’s instructions. Distance ‘H’ allowed is reduced by number of fittings, filters and valves installed in the line.
FIGURE 15: TWO-PIPE GRAVITY FEED SYSTEM
FIGURE 16: TWO-PIPE LIFT SYSTEM
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