Little Giant = Little Flow

[RNall]

I got everything on the 215 up and running this weekend. FINALLY :D
I had a little leak on the Dolphin return so I shut things down. I fixed the leak and powered everything back up. No leak on the Dolphin :D Then, I looked at the skimmer and it wasn't doing squat. It's powered by a new-ish Little Giant 4-MDQ-SC. It was running and sounded fine put was only putting out 75 gph at best. It wasn't cavitating, all the valves were in the proper postitions, etc. I then shut everything down again and took the pump apart on the Little Giant. It was a little dirty and there was a tiny stone stuck in between two ceramic impeller blades. Everything looked good though. There was no damage to anything. I cleaned it up, tossed the stone in the trash and put it all back together and powered it up. It's the same. <_< If it's not overheating, running 75-100 gph, not damaged and in good condition, what in the world is wrong with it? :huh Is there anything else I can do to test/fix?

Thanks,

[RNall]

No ideas?

I took the pump apart again last night and didn't find anything again. I put it all back together and now it is working at about 50% capacity. What in the world is going on? Perhaps I need to take the entire pump apart. I have not been removing the back end of the pump. It's not making any weird sounds or anything. Perhaps the back end of the pump is where it attaches to the motor's drive shaft. Perhaps however that is attached (set screw?) it is slipping?

Any ideas???

[seamonkey2]

hey Ron, if is an old pump, could it be that is dying?

or there is a loose connector?

how big and tall is your skimmer, each of mine are power by dart pumps

Jose

[RNall]

The pump is less than a year old I'm told. It looks new-ish as well. It's a Little Giant 4-MDQ-SC rated at 850 gph. The skimmer is a PM CV626 (venturi). It's 8" in diameter and 26" tall. Please see photo:

Thanks!

[Ed]

It looks like your pump goes through a valve and then an elbow (or two? can't see from the pic) before it enters the skimmer. If so, eliminating the elbows will dramatically increase your flow. HTH.

[RNall]

Sorry, should have mentioned that this is an old pic and that I have done this.... There is also a dolphin in there for the return instead of that mag18. Good point though. Any other ideas?

[seamonkey2]

Agree with Ed, elbows and tubing kills your flow, the skimmer seems small enough for the pump,

also the regulating balve should go the other way, so the water goes directly to the skimmer from the pump and the return is regulated by the balve, thats how I got mine set up.

Jose

[RNall]

Didn't mean to confuse on my last post. I have removed the elbows. The black line is the skimmer discharge. Just outside of the photo is a gate valve (to the right of the pic) to regulate discharge. Currently, the inlet to the skimmer (gate valve pictured) is wide open and the gate valve not shown for the discharge is barely cracked open.

[seamonkey2]

then sounds like the pump is dying, you want to try a mag 12?

LMK I got an extra one

Jose

[RNall]

Dying pump? I sure hope not but I do not have an explanation for what's happening... I think a mag 12 may be a little too stout for that skimmer. If I had to use it, I would definitely have to crank it down. The LG 4-MDQ-SC is the largest recommended pump. Well, wait a minute, I just found a Mak4 recommended and that's like 1100 or something. But I do not know if more is better in this case???? (sent PM)

Here is a bone head question. I have never had a Venturi style skimmer that I had had 'problems' with, therefore I haven't paid much attention. The venturi itself is simply a port to allow air to be sucked in (creates a vacuum as the water stream goes by) right? Well, this one is making quite a bit of noise and if I put my finger just over it, I can feel air coming in and much to my suprise, out. I had already checked to make sure it was clean. I can blow a ton of air in the skimmer without any effort really. So how in the world do I feel air coming out? Or am I out of my mind?

[seamonkey2]

sounds like you have a leak

try this,close the air inlet and if there still air going in, find the source, plug it and that should help.

Jose

[matt]

About your pump, if you've cleaned the wet end and you know that the impeller is in good shape and is turning easily on the shaft, there's not alot more you can do. You have to be sure to remove all traces of scale from the impeller and shaft, using vinegar or diluted muriatic acid. You probably know this already, and if you've done it, your next step is to call little giant, they area U.S. company so there's a chance you could send them the pump and they'll rebuild it. IMO they're medium quality externals; way better than mag pumps but not as good as iwakis or pan worlds. See what little giant says; they may rebuild it cheap. If not, go for a pan world. The genX mak4 is only a little more powerful; it actually runs on less power, but has 3/4" out rather than 1/2". Both of these pumps running correctly would put out more flow under any sort of pressure than a mag 12, so don't worry about that being too much pump.

About your venturi, I'm not sure how yours is set up exactly, but the general idea is that water flow speeds up in the area of the air inlet, creating a pressure drop which draws air in. It's not uncommon for there to be some whistling or some sort of air noise. You can quiet that down with a foam cover. (like a foam windscreen on a microphone) If you cover up the hole, the water gets clear, right? then you take your finger off and it get bubbly again? If so, it's working, and I suspect what you feel is not air coming out of the venturi, but just some turbulence right around there.

What I can't figure out from your photo is: 1) What's the white fitting up high on the tube? I would have thought that's where the water in would go. 2) Where the output is, it looks like there are tons of bubbles; does this skimmer drain microbubbles into your sump? I bet there's an elbow inside the tube at the output so it draws from the very bottom of the tube, but it still looks very foamy to me. This is one of the reasons I build a box under the tube on my skimmers.

[RNall]

sounds like you have a leak
try this,close the air inlet and if there still air going in, find the source, plug it and that should help.

I have plugged the air inlet and it stopped the air flow. I only did this for a second and wasn't checking for leaks so I will do that tonight. Thanks again Jose!


About your pump, if you've cleaned the wet end and you know that the impeller is in good shape and is turning easily on the shaft, there's not alot more you can do. You have to be sure to remove all traces of scale from the impeller and shaft, using vinegar or diluted muriatic acid. You probably know this already

yep. :)


your next step is to call little giant

I will do that. thanks for the idea!


If so, it's working, and I suspect what you feel is not air coming out of the venturi, but just some turbulence right around there.

I will check again.


1) What's the white fitting up high on the tube?

Its a second port to be used for counter current action. These things come from PM with a tee off the bottom port and the top port tied into the bottom. I think it's supposed to provide 50 gph of counter current flow. I guess the previous owner thought it worked better without it.


2) Where the output is, it looks like there are tons of bubbles; does this skimmer drain microbubbles into your sump? I bet there's an elbow inside the tube at the output so it draws from the very bottom of the tube, but it still looks very foamy to me.

Correct, there is an elbow. This is an older picture, the LG isn't creating that much turbulence or bubbles right now. It does drop some bubbles into the sump but they go behind a baffle.

Thanks for all the help Matt!

[RNall]

Well, I plugged the air inlet last night and there was no more air entering the skimmer. So no leak. I was hoping there was one...

There is definitely air occasionaly coming out of the venturi. It's like it burps up air every few seconds. Could something be lodged in it? I wonder what would cause this.

[matt]

Can you post a close up photo of the venturi? I'm not sure what would cause what you're talking about, but remember that a venturi will work best with a particular range of water movement through it and especially with a steady flow. It's all about how much speed the water picks up in the venturi area, and consequently how much of a pressure drop is created. So your pump may have something to do with the burping. A typical scenario is that air enters the water at the venturi, creating foam, which means the water column expands in volume right downstream from the venturi, which causes friction, and with a weak pump, a slow down of the water, which can cause the foam to "back up" a little in the venturi area and interrupt the flow of air into the water stream. So, this causes less foam, which lowers the line friction, it speeds up, and the whole cycle starts over. Does this sound like someting that might be going on?