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EK-Quantum Kinetic FLT D5 Pump/Reservoir Low Flow

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New Member
Nov 7, 2011
I recently bought the EK-XTOP D5 and I also bought the EK-Quantum Kinetic FLT Pump/Reservoir Body (120mm). This reservoir is listed as being compatible with both the DDC and D5 pumps. I was concerned about how this was accomplished since the two pumps have a different impeller and volute shape.

I was really surprised by how different the volute shape is between the XTOP and FLT. At least in the case of the D5 pump (I don't have a DDC). The volute on the FLT is tiny compared to the XTOP. I decided to do a simple flow test between the XTOP and FLT to see if there was an impact on performance.



I measured a 25-30% reduction in the flow rate between the two tops. The XTOP had a flow rate of 3.9 gpm (14.9 lpm) and the FLT had a flow rate between 2.7 gpm (10.4 lpm) and 3.0 gpm (11.4 lpm) depending on which ports were used. I was pretty disappointed.

I looked at the FLT top and thought I might be able to carve out the shape of the XTOP volute into the FLT acrylic. So that's what I did. I used the XTOP to trace out a stencil and transferred the profile onto the FLT.



A generous application of tape to protect the acrylic surfaces.


I used a Dremmel 117 bit to do the carving.


The true profile would have brought the discharge into the gasket groove. To avoid that I undercut the acrylic near the discharge. I also ported out the actual discharge to open it up and smooth it out.


It's far from perfect, but I'm happy with how it turned out.



I removed quite a bit of material. It's hard to see the profile in the after picture so I added an outline.


So what was the result? I reran my flow test and I measured 3.5 gpm (13.1 lpm) or a 12% flow reduction from the XTOP. I think the improvement over the stock FLT is pretty good.


I'm not sure why there isn't a better volute profile from the factory. They already have the tooling to carve out an XTOP. I suspect the reservoir is optimized for the DDC pump, but I don't have a DDC pump to test.

Pumps want a straight unrestricted path to the inlet (Like the XTOP). There's a sharp 90 degree turn to the inlet in the FLT. The large open area around the FLT inlet may also cause some vortexing that impedes inlet flow. I suspect adding flow straighteners at the inlet would further improve performance.

Did I perfectly match the XTOP volute profile? Probably not. Other than the outline it was done by eye. Maybe it could be better.

This wasn't too hard. If you're handy I would recommend making this modification to your FLT reservoir.


Nov 14, 2003
Port n polish on a pump snail, I like it!


My guess with the weird volute would probably be like you said, to make it work for both the DDC and D5 pumps. I'm sure they had to find a happy middle-ground between the two pump volutes being effective to some extent, and then between machining costs/complexities. They clearly went the cheaper/easy route on the latter, a la no undercut. :p

Either way bravo on your modification, it's always good to see actual modding now a days. :cheers: