Filter stopping negative pressure

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onewheeld

Member
First time setting a tent up started off with cheap stuff and as ran into problems iv ended up with over the top stuff with the exception of the filter that’s still cheap.

Dr90 tent (90 x 90 x 185)
10” duct fan down to 5” reducer(1000m3/h?)
6” duct fan down to 5” reducer (800m3/h)
Darkstar air cooled hood
Ox ram 4” filter (needs replacing-no cash)
Passive intake
Both fans on controllers

More than enough negative pressure when the filter isn’t attached from either the 6” or the 10”, tent is almost imploding

6” is used as extraction
10” is cooling the hood

Attach filter and then the negative pressure is almost zero and this doesn’t matter if I use the 10” fan or the 6”

Tried both sucking through the filter and iv tried blowing through it

There are no leaks from the hood(i took the standard seal off and resealed it myself as well as tested it for leaks)

This is leading me to think the ox ram filter is a load of crap (cheap eBay buy)

From what iv read once setup is connected with the filter I should still have a stupid amount of negative pressure when using either of these fans

I’m out of ideas and I’m sick of buying tape now Could it be the filter is blocking so much airflow?have people seen this in the past? and are there any filters that you would recommend?
 
coreywebster

coreywebster

Well-Known Member
You don't need two fans in a 90x90 tent. You can use one fan to cool the hood and extract the air.


How do you know there is no negative pressure in the tent?
If you can feel air coming out of the duct end then its doing its job.

I can only imagine your using a 400w or 600w light in that size tent. A 6" fan should be fine.

Would like to see a drawing showing how its all set up, where the air is exhausted and where new air comes in the room ect.

Only other thing is to check there is no shrink wrap over the filter under the dust cover.

There are obvious issues with trying to use a fan far greater cfm than the filter, it cant take the airflow and it wont clean the air because contact time with the carbon wont be long enough. Having a huge step down with the reducers is going to strain the fans too.

I would consider sending back the filter and one fan and using the money to buy a proper size filter.
 
coreywebster

coreywebster

Well-Known Member
Just to point out, if you don't have an intake then its impossible to not have negative pressure, just because you cant see the walls pulling in doesn't mean you don't.
I would see what the temps are when the lights are on.

I used to use an 8" fan rigged up to 8" filter and pushing air through 3 cooltubes in an 2.4mx1.2m tent and that worked perfectly fine.
Unless your living in a really hot climate I don't see how a 6" fan with 800m3/h wouldn't do the job properly in a small tent.
 
coreywebster

coreywebster

Well-Known Member
As well as a diagram of your set up showing everything I would like to know exactly what fans you have. When folks say duct fan it worries me.
Duct boosters are not extraction fans. Hopefully you mean inline fan.
 
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onewheeld

Member
Sorry for the late reply Christmas holidays,

Yup I meant inline fans sorry for the confusion one is a system air (10”) the other a vortex pro (6”

I can feel air coming out of the extract when the filter isn’t connected

When filter is connected I can’t

I tried smoking to see which way the smoke would go,filter off smoke is sucked through lower vent then up to fan and to extract with the filter attached the smoke doesn’t travel anywhere

Hadn’t thought of shrink wrap to be honest,the pre filter is off and nothing there but I’ll have a closer look just in case there is anything else where

I hadn’t thought of the speed of the fans effecting the cleaning system as iv been mainly trying to get my temps right but yeh that makes sense also

Yup I agree the 10” is losing a lot of efficiency but it came up cheap and I was running out of ideas

I more than likely will sell it,I just want to get these temps sorted 100% before I make any further decisions

I have tried all except for the filter connected to hood configurations I can’t remember the temps now although all were too hot,I’ll try the filtered hood method shortly using the 6” and let you know.currently set up as below as all guides say to keeps hood and filter separate to keep temps down OTT I know

Cool intake (same room) —>10-inline fan—> hps hood—> ducting hot air to a t-piece —> vent through window

Filter—> 6”inline fan —>ducting out of tent to the t-piece—> vented hot air through window

Passive intake is again room temp

Room is generally 21 degrees(70.3f) most of the day then drops slightly at night as I have the window open when lights are on

I’ll try swapping things about now and let you know how I get on

Cheers for the replies :)
 
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onewheeld

Member
Would you run filter at the base of the tent to bring in cool air to the hood or leave the filter at the top then through the hood iv seen it done both ways but wouldn’t the second make the hps run hotter?

Also pulling air from the tip of the bulb to the socket or from the socket toward the tip iv read it makes a difference personally I can’t see it doing
 
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onewheeld

Member
Ok so iv changed things around it’s now setup as advised

Room temp 21.5 Celsius or 70.7 Fahrenheit @lights off
time now 18:55

All Vents closed
Hps @400w
Slight negative pressure,
Filter at base of tent->ducting->hood->ducting—>6” fan (inside top of tent)—> ducted straight out of tent—>out of open window

Door to room that tent is in is closed

Lights came on at 19:00

I’ll update room temp and tent temp in an hour or so
 
coreywebster

coreywebster

Well-Known Member
No I would still have the filter high up, when cooling a light its not the air temp of the air going over the light that matters, its just the fact air is moving over the light, collecting some of the conducted heat from the bulb with it so it doesn't matter if the air is cold, warm or hot really, it still gets raised by how ever many degrees as it passes over the bulb. Air cooling is about removing the heat from the room rather than cooling a bulb. It still takes approx. a third of the heat out of the grow space.
It is important though to have the filter high up, although some people are forced to have it low, removing the warm air in the grow space from where warm air ends up, high up.

It does sound like the filter could be bunged up, if its cheap it could be blocked with smaller particals of carbon.
The obvious answer is to buy a better filter of a bigger size. But if funds are tight then the next bet thing would be to empty the carbon out and refill it with some new stuff. The issue with that is its a messy job which will involve drilling out the rivets and then been careful to refill it 100%, if its not full then you get gaps and although that would give less resistance on the fans and allow better airflow it would stop the carbon cleaning the air.

I asked about how your set up was rigged because I thought it might be possible that having one large fan pulling air from a room and having a small fan (with reduced performance due to filter) pulling in the tent that both fans may be working against each other, as one cooling the light would draw from the room, the small fan with filter would be trying to pull from the tent, the tent then has passive intake relying on negative pressure but the bigger fan pulling from the room would be create more negative pressure on the outside of the tent. Effectively working against each other and the bigger fan would win the battle stopping negative pressure in the tent and putting strain on both fans.

Anyhow im rambling now, been smoking since 8am.
:bigjoint:

Let us know if you have any luck with the new set up.
 
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onewheeld

Member
Right ok I’ll move the filter up top I was under the impression cooler air for the hps would be better but that clears that up

Your point about the fans working against each other also makes sense and highly possible that I could of had leaks in the tent from the reflector forcing more air in then the extract could handle

I think the filter is really affecting this setup room temp now hasn’t changed but temps inside the tent are mental

Time now 20:15
Room temp is 21.2c/70.16

Slightly lower room temp now as window is open

Temps inside tent are:

Bottom:30.5/86.9
Mid:29.5/85.1
Top:30.7/87.2
 
GreenHighlander

GreenHighlander

Well-Known Member
onewheeld said:
Filter at base of tent->ducting->hood->ducting—>6” fan (inside top of tent)—> ducted straight out of tent—>out of open window
Click to expand...
I would leave the filter at the top as corey had said above. But I would put the fan right after the filter. I tape the two flanges together. I do that because that way you are pushing the hot air out instead of pulling it through your fan. It certainly helps the fan in the long run. It also makes sure that you aren't sucking stink through any leaks in the ducting.

Cheers and goodluck :)
 
coreywebster

coreywebster

Well-Known Member
Yeah with a working 6" fan and only a 400w you shouldn't get such temp rises.
You need to measure air temp in the shade though, not direct light, but even so pretty sure your right in thinking the filter is to blame.
I suspect its just full of carbon dust instead of quality carbon blocking all the air. It should only reduce fan performance by 25-40% when working properly.
You could run without a filter for a few weeks if your not flowering. Certainly wont hurt if your plants are either seedlings or tiny clones, when they get bigger they do smell even in veg. Might buy you some time to get a proper filter sorted.
Not sure where you are in the world but rhino pro, phresh or mountain air are top end. Its one of the things I would never go cheap on.
 
Failmore

Failmore

Well-Known Member
Inline fans are trash...you wasted your money. Buy a blower.

An inline fan is not designed to force air into a filter or pressure. Just to move some air.

IMO you will not solve your issue with those fans. Look at the blades inside. They are not tight, the air gives zero fucks about those fins when under pressure.
 
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onewheeld

Member
Yeh I’m currently in flower I did manage to get temps down quite a lot using the separate systems but still not enough for where I’m happy I’m just riding this out now I’m not expecting anything from this grow temps were fine when I’m veg but not really where I’d like them for flower I’ll just have to buy a filter and given the last post another fan/blower
I’ll see if I can attach pics of the fans in a sec
 
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onewheeld

Member
They are inline duct fans as far as I’m aware. From what iv read these are the style that are recommended. I know the ones you posted look like cheap Chinese shit and I never considered entertaining one. I doubt they would cool a computer tower let alone a tent

Let me know what you think.im a squid so willing to listen to any input from people with more experience
 
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