Tent Negative Pressure -- How Much is Too Much?

[jawnroot]

I'm putting the final touches on my new grow space. The flowering chamber is a GL60 tent. When I kick the fan on, the walls of the tent suck in a bit. I have two intakes 3"x12" and one 5" round intake, all covered with high-flow carbon filters.

I started with the 5", then added one 3"x12" then another. It seems no matter how many intakes I add, there's still that "suck in" effect. I know negative pressure is desirable to a certain extent; for those of you with tents, is this normal?

Here's a pic to illustrate what I'm taking about:

 

[etinarcadiaego]

Hmm, I'm not sure you can have too much neg pressure, can you? What would be the down side?

I'm in an airsealed cab, sealed except for a 6" intake. It's 36 cubic feet and I pull about 400CFM through it.

 

[Seismic]

My secret jardin dr100 (3.3x3.3) with an 8" elicent does that big time, and with no problem that I have found. Take care

 

[jawnroot]

I guess with a tent that has fabric walls, if there's any amount of negative pressure, even a small amount, the walls will suck in. It's not a major deal or anything -- the walls only suck in about an inch or so -- just wanted to verify I wasn't doing something wrong.

 

[dongle69]

Too much for too long will rip your fabric at the seams and/or screw up your zippers.
It is too much if the tent material is tight when sucked in.

 

[GOOROO]

you also don't want quite that much because if your tent is bowing in then your fan is working unnecessarily hard, which will def decrease the lifespan, effectiveness etc

 

[etinarcadiaego]

you also don't want quite that much because if your tent is bowing in then your fan is working unnecessarily hard, which will def decrease the lifespan, effectiveness etc

Hmm, interesting point.

Most inline fans, like Vortex, or CAPs Valuline stuff can handle high levels of static pressure, they're actually designed too.

Determining static pressure is kind of a bitch. There are explanations all over the web, but you'd really need to put some time in to it as the formula is complex, and to be honest I just don't care that much, lol.

Still, I wish there was some simpler way of knowing the pressure created . .

I would agree with what others have said in that since there is no reason to have an excess amount, and that it may damage a fabric tent, try to keep the tent loosely "sucked in".

My cab is made from oriented strand board, and is totally solid and seam sealed, so i can't speak from experience as far as tents.

 

[GOOROO]

what kind of fan are you using jawn root and how many cfm

 

[etinarcadiaego]

Yah, and what's the CFM rating on those high flow filters, do they say?

 

[Hemphrey Bogart]

Too much for too long will rip your fabric...

 

[jawnroot]

what kind of fan are you using jawn root and how many cfm

Elicent 150 CFM. When the walls go in, they're not bass drum tight or anything, and there's little if any tightness at the zippers. I can't imagine this amount of pressure causing any damage to the tent.

 

[etinarcadiaego]

well, your tent is 24" x 24" x 63", which is 21 cubic feet.

So if your fan had zero resistance it would exhaust your tent once every 8.4 seconds or so. It's safe to assume your filters are slowing the fan, but without knowing the make/model of the filters it's hard to know how much.

I'd say you're alright. You can use a speed limiter/controller on the fan if you're really worried

 

[Chem&M]

This never caused a huge issue in mine, but it evened out when I upped the intake a bit.

 

[Puff Daddy]

I personally use a small inline fan for intake, then use a speed controller on my exhaust fan to dial down the power until the appropriate amount of negative pressure is achieved.

Prolly your best bet if you're really concerned about it, but with just 150cfm on a filter in a tent that size, you're not gonna bust out the seams.

 

[humble1]

i was hoping that this thread would be about the effects of negative pressure on plant growth. something along the lines of increased transpiration or metabolic rate... hmmmhhh always wondered about that.

 

[HIGHGROOVE]

ya i used a speed controller also for my 8 inch max fan until it killed two fans the speedster

 

[geopolitical]

Tent Negative Pressure -- How Much is Too Much?

Crank it up till your tent collapses. Dial it back a bit, go buy a new tent. Now you know how much is too much.

 

[jawnroot]

Yah, and what's the CFM rating on those high flow filters, do they say?

I'm not sure. This is a link to the product:

WEB Absorber

I'm cutting it to fit the intakes on the tent. There's upwards of 90 cu/in of intake surface area.

 

[jawnroot]

Crank it up till your tent collapses. Dial it back a bit, go buy a new tent. Now you know how much is too much.

The fan is running full tilt right now...so I guess by your reckoning I'm okay?

 

[stoney917]

just keep aneye on humidity i noticed my humidty got really low when the fan went on bought a speed controller and its all good