Return pipe pinch point and effect

[wickette]

Technical question: I'm refitting a DIY canister filter for a larger tank. Was using 3/4 PVC for intake and return.

I need to put a union on the return, doesn't matter where it goes, the inner diameter is over 0.14" narrower than the pipe, Will there be less pressure put on the pump/tubing if the narrow spot is closer or further away from the pump?

 

[KrisReef]

This is a great physics and engineering question. I’m a biologist but I would guess that the closer to the return pump would be optimal for moving the pump (replacing or maintenance) and that the decrease in size over a few inches would be a negligible amount of pressure loss in your system.

What is the real answer? Let us see- bump!

 

[All_talk]

Theoretically the pressure drop across the orifice (restriction) is only related to the geometry of the orifice and the velocity/volume flow through it. Since water in not compressible (at least not at these pressures), the volume flow is the same at any point in the pipe... it doesn't mater where you put it.

 

[wickette]

This is a great physics and engineering question. I’m a biologist but I would guess that the closer to the return pump would be optimal for moving the pump (replacing or maintenance) and that the decrease in size over a few inches would be a negligible amount of pressure loss in your system.

What is the real answer? Let us see- bump!

I think it doesn't matter, and found a screw on repair coupling with a normal pvc pipe inner diameter that does the same task as a union so it's not an issue anymore, but just for semantics.

I'm not concerned about overall system pressure but specifically pressure on the pump.
I have 5 inline fountain pumps, all of them use the same horrible mechanism for the intake adapter/impeller covero, it's not threaded just a 1/8 turn. It's fine under normal conditions, as the tubing becomes inflexible over tine it applies more force on the fittings. I dont know its hapenibg til one day i go under there and see the pump lifted up on one edge. Again it's fine as long as it's not moved and stays on.

Tubing is pulling on perpendicularsides, if I'm lucky the output is pulling clockwise, no problem. If it's pulling counter clockwise back pressure unscrews the intake adapter.

I tried attaching the pump to the stand in my prototype 6 years ago, over time the fitting start to crack the threads on the pump causing steady dripping.

 

[Crustaceon]

Technical question: I'm refitting a DIY canister filter for a larger tank. Was using 3/4 PVC for intake and return.

I need to put a union on the return, doesn't matter where it goes, the inner diameter is over 0.14" narrower than the pipe, Will there be less pressure put on the pump/tubing if the narrow spot is closer or further away from the pump?

The pressure should be the same regardless of position due to the incompressibility of water. FWIW a .14" difference in diameter isn't going to have a noticeable affect.