Anyone know anything about vacuums & pressure relief?

[paperfist]

I built my own shop vac type of vacuum with a 25' hose to clean around the shop.

I used a pretty heavy duty container for the vacuum, but I'm worried if the hose gets plugged that the vacuum motor will exert too much pressure on it that the container will implode killing me and I'll live on in infamy with the newspaper article describing my death.

I tried looking around for some kind of pressure relief valve, but I'm not sure if that's what I need or something else to open up and let air in. Most of what I found is industrial in nature.

Thanks!

 

[Paperdoc]

What you fear is HIGHLY UNLIKELY.

The factor involved is the pressure DIFFERENCE between the inside and the outside of the vacuum container. The pressure outside it is normal atmospheric pressure, which is about 15.7 lb/square inch. The LOWEST possible pressure inside is zero - a perfect vacuum - and that is really impossible to achieve with a blower fan system. So the max pressure DIFFERENCE you are facing is about 15 psi. Can't possible be more.

Now, what kind of dirt container have you used? If it's a steel drum with moderately thick walls and headers, you are not going to cause it to implode with a 15 psi pressure difference.

"High Vacuum" is not at all like "High Pressure". With a compressor you can create air pressures many times normal atmospheric pressure. You would not be surprised to read a compressor tank output pressure of 150 psi, which is TEN times atmospheric. And I bet if you had compressed air being supplied to you at 15 psi, you'd think "no big deal". Your car tires are over twice that pressure! That's the kind of pressure difference you are dealing with.

Actually, when people worry about plugged vacuum hoses it is for a different reason entirely. Most vacuum systems use the flow of air through the dirt container and the motor and out to the room again to cool the motor. That's why the exhaust air is warm. If the system runs for long with a plugged hose, the motor is not being cooled properly and can be damaged.

 

[IronWing]

^^ This is simply incorrect. A 15 psi pressure difference is sufficient to destroy containers and the larger the container, the greater the energy release when it fails. In grad school, the student in the next lab over managed to catastrophically implode a vacuum chamber made from a 12" PVC diameter water main pipe, and yes, it did blow shrapnel all over the room, destroying other equipment.

OP, what is the container made from and how big? Maybe install a relief valve from a water heater backwards?

 

[Micrornd]

Most good central vacuum systems deal with this.
It's as simple as this - http://www.centralvacuumstores.com/...ve-srv-white?gclid=CMGo9IKInNECFVc7gQodX34DCw

 

[paperfist]

^^ This is simply incorrect. A 15 psi pressure difference is sufficient to destroy containers and the larger the container, the greater the energy release when it fails. In grad school, the student in the next lab over managed to catastrophically implode a vacuum chamber made from a 12" diameter water main pipe, and yes, it did blow shrapnel all over the room, destroying other equipment.

OP, what is the container made from and how big? Maybe install a relief valve from a water heater backwards?

That's exactly what makes me nervous. I've seen videos of ribbed steel drums develops a small dent and the vacuum just folds the drum onto itself.

The first barrel I used was a Rubbermaid Brute container which I thought was pretty beefy. Not so, it lasted a minute before it collapsed.

After a little research I found some people using these: http://www.homedepot.com/p/Everbilt-18-in-x-22-in-Sump-Pump-Basin-SF20/204733081

I made the top with 2 - 3/4" plywood sheets glued together with construction adhesive and 3/4" bolts. It seems to be holding up, but I would be more reassured with a safety device.

I have thought about a water heater relief valve, but I think those are set to a certain amount of pressure and I'm not sure how to translate that into vacuum pressure.

 

[paperfist]

Most good central vacuum systems deal with this.
It's as simple as this - http://www.centralvacuumstores.com/...ve-srv-white?gclid=CMGo9IKInNECFVc7gQodX34DCw

Wow awesome thanks so much! I've looked at a bunch of central vac parts diagrams but I guess that not being part of the actual vacuum it's not shown. I was wondering how they dealt with excessive pressure.

 

[IronWing]

If your container can flex and collapse it isn't likely to cause injury or damage. Brittle containers that fracture are more of a concern.

 

[paperfist]

If your container can flex and collapse it isn't likely to cause injury or damage. Brittle containers that fracture are more of a concern.

This container is plastic. I want to prevent it from collapsing entirely.