914 fuel pump system

The pumps are Medium pressure pumps capable of 25+psi.
The system pressure is reduced and regulated by the Fuel pressure regulator.
The fuel pressure regulator bypasses the excess fuel back to the Fuel Tank.
This is the same system used on 99% of all vehicles on the road today.

Series or parallel makes no difference when only one pump is operating.

If BOTH pumps are operating in Parallel, The fuel flow will be doubled and the Pressure regulator may become overwhelmed with the excessive Fuel Volume.  The pressure remains nominal but both pumps will be pushing hard against the head pressure.
The current draw will be MORE than Twice a single pump alone.

If BOTH pumps are operated in series the total flow volume remains the same as a single pump alone.
The pressure regulator operates normally.
The head pressure is shared by both pumps and the electrical current draw will be LESS than Twice a single pump alone.

The fuel pump design shown in the manual is correct.
Don't mess with success!!!

Thanks Bill.  I did find some fuel blocks / manifolds that makes the Rotax system neat and manageable.  So I will be doing the recommended system.  I would think that the series configuration would double the pressure when both pumps are on.  Since this setup has been used with no issues for a long time, I can't argue with success.

Allan

Series pumps WOULD be capable of double the pressure if the flow were reduced to Zero but the active pressure regulator maintains the flow at a constant rate and constant pressure.
The return flow to the tanks is considerable.
The pumps move ~ 30 gallons per hour while the engine uses less than 1 and up to 5 GPH at the most.
25 or more GPH of fuel gets continuously recirculated.

When Both pumps are ON the flow rate only increases slightly because the pumps are of the Positive Displacement design and each pump's speed only increases slightly when Both pumps run.

Allan, can you please provide a link to these manifolds/fuel blocks? Thanks.

The first picture is from a catalog.  I am waiting for the parts.  Using a right angel fitting on one end to give me the fourth port.  After ordering the manifolds and fittings I realized that I can not make it look like the second photo exactly.  Need the four ports on one side but the other side needs two separate two port manifolds.  I will have to cut one of the manifolds in two and seal up cut ends.  Hope that will work out OK.

The second picture was sent to me from a Rotax rebuild company of a homemade system which inspired me to get the manifolds.