Laguna 2900 = SP4??

rockskimmerflow · Sep 1, 2018

@jda I remember talking with you about your laguna 2900 and I finally bit the bullet because of it's slightly higher head pressure rating than the SP6 and SP4 pumps I very frequently use. I also very distinctly also remember seeing the spec being 135W and that matching the spec for the SP6 making me think they used the same motor block. Turns out that was false, at least in the current model 2900 laguna is shipping.

So I bought 4 Laguna pumps - all 2900 models - and they each have 112W @ 1.8amps on the label. Can you confirm if your OG 2900 has the old 135W rating on it? And if possible give me a rough measurement of the block width?

The pumps I have match the dimensions of the SP4 model. The impellers and rotors are identical to the SP4. And the volutes are interchangeable. I just can't wrap my head around the 88W vs 112W respective ratings of the SP4 and 2900 pumps. Is there some electrical throttling/trickery going on in the SP4 to keep its power below a level that would threaten the SP6? Or is there perhaps a totally unique set of switching controls and stator laminations in the 2900 that just fit into the same housing as the SP4.

In any case, it is quite interesting to me that the SP6, SP4, and 2900 (perhaps other models too) all use the same exact impeller design, with the SP6 just having a substantially longer and heavier rotor assembly to drive it in the much bigger motor block. If anyone has any info on these discrepancies between the 2900 and SP4 pumps I'd love to hear. Going to do some real world flow and electrical consumption tests in my system since the pumps are swappable for the same duty. Will report back on the results.

Dsnakes · Sep 2, 2018

I’m not sure if he has info on the descrepencies noted on the 2900 and sp4 pumps, but @Crabs Mcjones is interested in these things.

Crabs McJones · Sep 2, 2018

Not sure, but I'll follow along for your test results

rockskimmerflow · Sep 3, 2018

Some preliminary findings and some more questions that I will have to dig a bit deeper into have emerged. So far it appears the SP4 is a Laguna 2900 in motor block and impeller/rotor assembly. Of course, the 2900 has its 25' power cord and silicon carbide or alumina (can't remember which) bearings instead of the 6' cord and full ceramic bearing set of the SP4. I did find some old ad material and specs on the web that list the 2900 as 135W, 130W, 125W, and 112W in its current form. I can only imagine the higher power listings were for an older model. Will need someone with a legacy pump to chime in and confirm that suspicion of mine.

For testing I swapped the rotor/impeller assemblies to start with and they appear to be identical and I could not yield any difference in testing between them so I would consider those items interchangeable and the only difference being the front bearing of the 2900 is that other carbide or alumina material to match the rear shaft bearing in that pumps rotor well. Now, the interesting results began coming in when I switched the volutes: First test, Laguna 2900 motor block and impeller wearing SP4 front cover/volute assembly attached directly to the same union that feeds a 1 inch line to a couple of tanks in my grow out array. It is under a decent amount of head pressure (impossible for me to accurately calculate but irrelevant for the test since it is a constant variable) so the electrical draw will be down a bit from the 0' head spec listed on the box of the pumps. Kill a Watt meter was used - so take all these readings with a grain of salt in terms of being dead on accurate. The numbers listed below are the average reading I saw the pumps settle into after about 10 mins since they are 'smart pumps' and supposedly adapt to maximize their efficiency once put under a given head pressure.

Volts: 116.1, HZ: 59.9

L2900 (stock): Watts 67.7, Power Factor 0.58, Amps 1.05
L2900 (SP4 volute): Watts 53.7, Power Factor .48, Amps .92

SP4 (stock): Watts 54.2, Power Factor .52, Amps .89
SP4 (L2900 volute): Watts 65.6, Power Factor .60, Amps .98

Just for a laugh I threw an SP6 with a 1 inch barb outlet into the test and got these numbers. Watts 80.9, Power factor .60, Amps 1.2 - Interestingly, Just by the feel test I'd give the award for best pressure out of the eductors to the stock 2900 over the SP6 despite it's higher power draw. I think the head pressure in my usage case here is beyond what the SP6 is happy with.

Now not all those power factor numbers quite jive exactly with the amps and voltage readings I was getting for the given watt readings, but I chalk that up to the way in which the Kill a Watt measures certain things and likely is thrown off by the type of power usage by these synchronous reluctance motor pumps and their necessarily low PF ratings. I am intrigued by the readings and will need to dig a bit deeper to determine whether there are any substantive electrical tweaks between the motor block shipped with the SP4 and the 2900. Currently it looks like you can turn your SP4 up to 11 (11,000 lph that is) if you just buy a Laguna 2900 replacement volute and snap lock barb. So long as you're comfortable plumbing with flex hose then that will work a treat. My next experiment will be a mod to the restrictive volute shipped on the SP4 to see if me and a little dremel and polishing work can bring that up to 85 to 90 percent the performance level of the 2900 without too significant removal of material. I suspect I can do it fairly easily.