Fuel Pressure Spike, Injected, with Red Cube location change

[mdevans9]

So, just changed the Red Cube location on my IO-360-M1B from between the engine-driven fuel pump and the servo, to between the servo and the flow divider. Previously, when the Airflow Performance pump was turned on, the pressure rose from about 28psi to 30psi, with no spike. After the change, when the pump is turned on, fuel pressure spikes to about 37 psi for about 2 seconds, before falling back to 30 psi. The fuel pressure line is just after the engine-driven pump (3" or so), unchanged from before.

Somewhat concerned about this. Would appreciate any expert explanation, advice.

Thanks!

Merrill

 

[Avanza]

Pressure spike

Liquid is not compressible. Think of an iron bar moving inside a pipe.
If 100 % LIQUID in a pipe, there will be a spike when you start a pump.
This is why there should be a restriction in the fuel pressure line, so the spike
is dampened out as much as possible. Restrictor 0.03" or so.
If 90% LIQUID in a pipe, the air bubbles will implode when the pressure is increased when the electric pump starts and this will dampen out the pressure reading on the fuel pressure instrument.
I would not be worried from your description.

Good luck