Flowrates with Eheim 1250 and DD TDX, Maze4 and HC

W

whitewale

Limp Gawd
Joined
Jun 23, 2004
Messages
259
Still missing some parts on my project, so I went and measured the flowrates to at least get something going. I first installed a Dwyer RMC flowmeter inline to get accurate direct readout. Connections were made with 1 ft 1/2" ID tygon tubing, the pump was imersed in a large reservoir to eliminate an yhinderance on the suction side.
Flowrate with just the RMC: 3 gpm
added TDX block:2 gpm
added Maze4 block: 1.75 gpm
added 77 Boneville heatercore: 1.5 gpm
Now, the Eheim 1250 is supposed to deliver 5 gpm, quite obviously the flow meter is strongly restricting the flow. I therefor repeated the series without the flowmeter by measuring the time it took to fill a 1 gal container.
Just the pump: 12 sec = 5 gpm
added TDX block: 29 sec = 2.1 gpm
added Maze4 block: 34 sec = 1.8 gpm
added heatercore: 38 sec = 1.6 gpm
repeatability was +- 1 sec
I also measured the other two components singly
Maze4 block: 22 sec = 2.7 gpm
Heatercore: 23 sec = 2.6 gpm
Quite obviously the Eheim 1250, despite being rated a rather substantial 300 gph pump, does not have the power to drive water through a TDX block at the reported 3 gpm max flowrate. Adding the GPU block and radiator inline has comparitively minor effects on the overall flow in this configuration, as has the flowmeter.
Surprisingly the flowmeter does add a lot of noise to the system, so I will not make it part of the final design.
I will add data on different parallel designs later.
 
this has been done before. 5 gpm is only at 0 head i believe? max flow at 0 head means nothing, its all about the max head flow.
 
Sounds pretty reasonable to me. The 1250 is not a pressure rated up, and therefor, as you put some resistance to the flow of water the volume drops dramatically.
 
interesting...however my 1250 pushes thru my S-TDX just fine...however I am still going to get a higher head pump
 
Played with parallel configurations this weekend. If I put the TDX in one loop and the Maze4 and the heater core in the other I get a very even 1.5 gpm through both loops, for a total system flow of 3 gpm. This would give a theoretical advandtage over the serial flow since the GPU gets "cold" water not preheated by the CPU. Unfortunately the total flow through each subunit is still the same 1.5 gpm as the serial system. It also adds an additional 4 leak points to the system, and trying to get 4 1/2 ID hoses into the case is very cumbersome. So, until I can get a stronger pump I will go with the serial set-up.
 
I still don't think anybody understands pump laws. It doesn't matter what final pressure the pump puts out following installation into a system. Just realize that the the pump output pressure is a function of the total system resistance and the intersection of that curve (versus flowrate) with the pump flow curve (manufacturer supplied data). Ahhhhh! Does nobody understand this! And PLEASE, don't try to explain what you think you know to me....I've had a lot of training on thermodynamics, hydrodynamics and fluid systems.
 
Now, freecableguy, if you could please give me a proceedure to determine that intercept between total system resistance and pumpflowratecurve from theoretical values without running the experiment I'd be extremely greatful. Would probably save a lot of people a lot ot time if you have a simple numerical program for that, parameterized for the individual components.
 
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