# Confusion about pressure drops and pressure regulators

## Main Question or Discussion Point

When designing the fuel plumbing for an efi system, do pressure drops in the fuel lines need to be considered when there is a pressure regulator? If so why? Been reading up a lot on plumbing design lately about how the goal is to minimize restrictions in the lines which ultimately cause pressure drop and play a large part in what size fuel line to use. I've read that the smaller diameter the line is, the greater the pressure drop will be. But if there is a pressure regulator, why does considerations about pressure drops and line sizes matter? Thanks

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Do you mean that smaller diameter increase the pressure drop? I think to increase the pressure (reducing pressure drop) a reducer is needed, in other words using smaller design is better.
For your question, in my opinion, regulator is used to overcome the pressure drop and to increase the flow of fluid.
Sorry if my grammar is bad.

CWatters
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if there is a pressure regulator, why does considerations about pressure drops and line sizes matter? Thanks
Many simple regulators can only reduce the pressure not boost it. So they need a supply pressure that is higher than the target output pressure. If the pipes between pump and regulator are too small or there are restrictions in it then the pressure going into the regulator might be too low.

Many simple regulators can only reduce the pressure not boost it. So they need a supply pressure that is higher than the target output pressure. If the pipes between pump and regulator are too small or there are restrictions in it then the pressure going into the regulator might be too low.
So let me see if i can now explain how the fuel system works now with the pressure regulator mounted at the end/after the fuel rail. Fuel is pumped out of the pump at a certain pressure through the fuel lines and up into the fuel rail all the way to the pressure regulator. The fuel in the rail is above the desired pressure for it to be delivered to the injectors so the pressure regulator will reduce it to the desired pressure for the injectors which will result in excess fuel being returned to the tank through the outlet of the pressure regulator. Thats why the fuel wants to be delivered to the fuel rail and regulator above the desired pressure so the regulator can precisely lower it and give the injectors an accurate amount of fuel. If the fuel pressure in the rail and up to the regulator is below the desired pressure for the injectors, the injectors will not accurately get the correct amount of fuel and no fuel will be returned to the tank. Which is why a powerful enough pump is needed along with keeping pressure drops in the plumbing system to a minimum is necessary to make sure the pressure is high enough to activate the regulator so it can accurately lower it for the injectors. If the pressure is not high enough when delivered to the rail, the engine will run lean. Is this correct?

Last edited:
CWatters