9420 skimmer depth

[Macca_75]

Hi Roger,

I know I have read it here somewhere before but I can't for the life of me find the post.

What's the "optimum" depth for the 9420 skimmer?

I've picked up a new hydro former as suggested last week, have plumbed in the sump to hold it and just need to set the depth of the baffles. Currently set to 205mm so I can go upwards from there.

Cheers

Adam

 

[rvitko]

I would regard 200-255mm as the ideal for this model.

 

[Macca_75]

Thanks Roger.

So based on this....

Last night I started to run the skimmer to break it in at 280mm deep. The water level was approx in line with the top of the hydrofoamer. I noticed:

1) The overflow system was in use 100% of the time, pouring out.
2) I had the air turned right down using the clamp.
3) The water it was in was mostly NSW (disconnected from the Display for last night) so I didn't expect anything in the cup.
4) the skimmer was not quiet. I did notice that the silencer had water in the bottom 5 mm or so and was making a constant slurping sound. Is this normal? I have the hydrofoamer connected to the silencer (at the right angle end) and the run the tube through the holder on the body and the clamp up near when the airline joins the body. Does this sound right and will it quieten over time? If I drop the level of the water so no water is going bacn down the airline will it fix that slurping noise?

Will lowering to 200mm be OK for the hydrofoamer? Last thing I want to do it run it dry.

Thanks in advance.

 

[rvitko]

1)This will generally mean a surfactant was present in the water, new filter bag, new floss, an additive of some sort. The best fix is to close up the air about 50-75% and remove the airline from the nipple on the skimmer body. It should then remove a watery skimmate and after the substance is removed it should work normally.

2) Keep in mind less air equals more water, the best way to think about is as a roughly 2500lph pump and you are just adjusting the ratio of air to water, while not exactly correct, it can do about 3500 lph of water fully closed or 850lph of air and 1400lph of water fully open, it is roughly the relationship. Closing the air does tend to create more violent water flow so closing it too much will actually make things worse.

3) NSW may have some skimmable plankton and other organics and if it was treated in anyway this can also be a cause.

4) When the antioverfoaming system is activated and water is going through the air passage it is noisy, disconnecting the airline from the body under the cup will let you bypass this for now. Once you skim out the substance causing this issue it should work normally. Dropping the water level may help, the pump should be at least 1/3rd under water and 1/2-3/4 is the best. The antioverfoaming is a feedback loop where a change in surface tension constricts the air by allowing water to rise and plug the air, it does produce noise, but it also prevents a foam over. Any colloid or phenol type substance will cause this response so can a very heavy organic load.

 

[Macca_75]

Thansk Roger. I did run it for a few hours last night and it seems to be getting better. I will drop the level tonight and open the air even more (it's turned way way down).

Seems to be sorting itself out and is already skimming. In approx 4 hours it took about 10mm of tea colored skimate into the cup - great result with the air turned all the way down.

Once I drop the water level a bit (currently running at the top of the pump) and run it 24x7 I'm sure it will work like a gem.

Thanks again

 

[Macca_75]

Hi Roger,

Just a quick update/question.

The skimmer has been running fine for about a week now, although it continues to run with the "antifoaming" active.

If I disconnect the hose I get a light tea coloured skimmate and the cup is full to the brim in around 10-12 hours.

If I connect the hose to the chamber the skimmate is far darker, however I only collect about 10mm or less in the same period.

The air is full open and I am running the water level approx in line with the top of the pump (trying to get it to skim a little wetter with the hose connected to the body).

Is there anything else I should be doing or just be patient and give it a few weeks? And if it is a waiting game, hose on or off the chamber (should I skim really wet or go for quailty over quantity)?

Thanks in Advance.

 

[rvitko]

I would run it connected, I think you are getting it straightened out, do make sure it is level. It is not unusual for some water to go through periodically, that is what it is designed to do, the water automatically restricts the air as needed to get the optimal tuning and avoid a foam over.

 

[Macca_75]

Thanks Roger. I'll try and post some relevant pics when I get home tonight.

It's level and running OK - albehit a bit loud due to the constant over foaming. Happy to leave it like this if it will eventually sort itself out.

 

[Macca_75]

Hi Roger,

Getting back to an old thread here. I am still having an issue getting this skimmer to run as I think it should.

Here is a pic of the depth of the skimmer and the colleciton cup after 1 week (sorry about the quality of pics).

It was about 500mls of skimmate.

Now I am happy with the quality and quantity of skimmate however the skimmer is still really noisy. The noise is all due to the "over foaming system".

I did clean the cup and give the skimmer a quick wipe with RO on the weekend straight after these photo's were taken (with the power off). To my surprise when I turned it back on the thing ran whisper quiet. The level of water within the chamber under the cup had dropped slightly (just below the air intake nipples) and the "over foaming system" was not being used (hence the redcution in noise). Within 1 day it had produced double the quantity of skimate as the pic above, albehit a very wet skimate.

I emptied the cup (didn't clean it or anything), put the cup back on and it started performing as it had previously, with the "over foaming system" feature active and noisy.

Any idea's on how to stop it overfoaming? And once we get that problem solved how many lower can I go without burning the Hydrofoamer out?

Regards

 

[rvitko]

If at least half the pump is submerged, you should be fine.

The problem with these skimmers is there is just enough variation between 50 and 60Hz models that it is hard for me to say with certainty what could be the cause. Have you checked that the air hose is free of any pinches or kinks? Is the filter sock retainer all the way down on the pipe? Keep in mind that as you cut airflow the water increases and if the water level is higher, there is less back pressure on the pump so more volume of air and water is added, the other possibility would be if the filter is up higher on the pipe, this would raise the internal water level. Make sure the pipe and filter sock is pushed in all the way.

 

[Macca_75]

Thanks Roger.

Interesting Observation - when I pull the hose off the nipple the level in the "overfoaming" chamber drops to below the nipple. It's almost as if there is a slight vacuum in there. (and the skimmer is whisper quiet with the hose disconnected).

A solution is to leave it like that, but I'd prefer have it connected "as designed".

Would the 240/50Hz model hydrofoamer run "a little harder"? Do you know what height the outlet pipe should be and is there a difference in required height between models if the 240v hdrofoamer performs different?

I also don't run the sock, but I have 2 foam pads wrapper around the outlet pipe. Since the water is already out of the system by then I don't see how this could affect anything.

Sorry to keep hitting you up, but there aren't a lot of this model skimmer over here in Aus. As I bought the unit second hand I have no idea what region it came from.

I have replaced the hydrofoamer with a new one from Aquadepot, however I reused the impellor so not sure what "region" that part is either. Are they different between models?

Cheers

 

[rvitko]

If I recall the US 60HZ pump is actually a hair stronger, about 5% or so. The pipes are the same and should be 22cm long.

So long as the foam is below the top of the pipe it should have no impact.

A correct 50Hz impeller should have 3 full rows of needles, they should all be the same length.

When you disconnect it, the skimmer gets all the air it needs, you are bypassing the anti over foaming system. It isn't so much vacuum as that the air flow is high and the water flow is less. I would check that the two other air intake nipples are clean and that the skimmer is level, if the skimmer was unlevel and this affected the drain of the upper chamber, this could be a cause.