pressure vs. circulation applications what's the difference?

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Dec 17, 2003
I've noticed that there are two different types of Iwaki pumps:

"RLT pumps are for pressure applications. RLXT pumps are for circulation and wet/dry return."

Can anyone help me to understand the differences between a pressure application and a circulation/wet/dry return application?

Which situations are appropriate or unique for the implementation of each application?

What other plumbing considerations are specific to each application?

Thanks in advance....


reefer addict
Aug 26, 2003
Portland, OR
Pressure= For return from a sump, like in a basement, to power a skimmer, or returning water from a sump and feeding other pieces of equipment, ie: skimmer, calcium reactor, pumping water thru a inline heater. Use's small ID hose or pipe

Circulation= like in a closed loop to get rid of PH's anything for non-pressure related. Use larger ID hose or pipe. Other pumps for circulation- Sequence and AMP master and others.

Most don't use the canister filter or a wet/dry for a reef, but maybe a FOWLR tank.

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Active member
Oct 19, 2003
Impellor Design

Pumps are designed to input energy into the fluid. This energy comes in many different forms: kinetic energy (velocity or flow rate), potential energy (pressure), thermal energy (heat), etc. Velocity and pressure are good. Heat is bad. If you look at your pumps specification sheet, you will see a series of paired numbers of "lift height" versus flow rate. The "lift height" reflects the pump's output pressure, where 1 psi is equivalent to 2.31 feet of "lift height", or "head". If you plot "lift height" against flow rate, you get what is called a "pump curve".

In a crude sense, it is the impellor and housing shape that determines wether a pump is a relatively high pressure pump or a relatively high flow rate pump. Pumps that do both are very expensive. If you look at the impellor on your aquarium related pump or your car's water pump, you, generally, will see an impellor with straight blades. These are low quality pumps that are designed to just move water, without producing much pressure. The inefficient impellor blade/housing design allows the water to "slip". This built-in inefficiency serves as "safety valve". If you were using a pump that head high pressure, your aquarium equipment, automotive radiator, heater core, hoses, etc. wouldn't last very long. A high quality will have curved blades, and may even have vanes in the housing.

Your typical hobbiest's pump will only lift water 5-10 feet in the air. Compare this "lift height" to your residential water pressure, which typically ranges from 20 psi - 80 psi, depending on the topography in your area. 20 psi will lift water 45 feet or so.

High pressure pumps, like those found in hydraulic machinery, put out pressures in the thousands of psi. These types of pumps are used to do work, such as lifting stuff.

If you need to push water through something with a decent amount of resistance, such as an reverse osmosis membrane, you may have to use a higher pressure pump, than say a power head. Power heads, with their straight impellor blades, pretty much are designed for recirculating water.

Have you noticed that pumps with more "lifting height" are alot more expensive?


Oct 30, 2003
Yep, good topic & Scat thanks for a through explanation but my truck has a high performance water pump, not cheap! LOL
That's why I really don't like PHs, the one Maxi I do have is one awesome PH for it's size, it runs forever LOL! Most of your submersibles are impeller driven, magnetic drives as compared to your larger more expensive externals like Sequence, Little giant, Iwaki etc. I also have a Tunze stream pump, I call it a pump because of the design , it uses a propeller instead of impeller, other than that it is basically a submersible pump/PH. Actually, if you compare a PH to these submersibles, they are one of the same just one is larger. If you want more power, you will leave this design behind for the external motors, higher torque ratings, can drive a pumps of either pressure or volume rated, and in larger amounts that would be impractical in submersibles, even though you have to admit they've come a long ways in the hobby!


Gaitor Wrestler
Nov 27, 2003
So for a sump return going into a spray bar. Would you be better off using a pressure rated pump or still using a circulation pump?


Jan 7, 2004
pressure rated pumps are good for both applications, but flow pumps should be kept to returns or closed systems...
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