Problem with my Venturi operated Drum Vac

[kdv1988]

Hey guys, I have built a Compressed air venturi operated Drum Pump for my garage. The system consists of a horizontal venturi tube with a pipe (shut-off tube) that is inserted into the Drum. Turning on the venturi creates vacuum in the drum and thus liquid is sucked from outside and is collected in the drum automatically. This pipe contains a float which moves up-down. Purpose of the float is to block the venturi when the liquid reaches up to the highest level in the drum to prevent overflow of the liquid from the drum. Since it is a purely compressed air operated system, there are no electricals and hence no switches. Attached are photos depicting my system, the float & a standard Exair Drum Vac.

https://ibb.co/fkd46kX

https://ibb.co/tCH67Qt

https://ibb.co/64fzFxV

Now, the problem I am facing here is that when I turn on the venturi, the vacuum sucks up the float and blocks the venturi immediately thereby stopping the vacuum generation process in the drum. Releasing the pressure causes the float to fall down in the pipe to its original position and ONLY then the system works (i.e liquid rises and the float rises along with the liquid and blocks the venturi when the drum is full).

The material used for the float is either Nylon/Teflon (don't know which as we have a bunch of either rods available with us) and the shut-off tube is SS304. What can I do to ensure the float ONLY rises up in the pipe along with the liquid? Im worried if I increase the weight of the float, it might not float on water and will remain seated at the bottom of the pipe.

I cannot invest a lot of money on an Exair system as we're a small shop and have most of these parts handy. I feel like I am missing something rudimentary here and some guidance will be really helpful. Thanks!

 

[kdv1988]

Okay.. not sure if it'll work, but I have thought of something. What if I give the float a tapered top, with the tapered end entering the 11mm ID of the Dip Tube.. And I make a groove on the float at the interface between the 11mm & 12mm ID sections and attach an O-Ring.

Attached sketch for reference.

EDIT : couple more ideas.. Attached.

,

 

[LittleInch]

The thing is as the water level gets to the float thing, it will be sloshing around and moving and some water will inevitably escape and get into the air holes.

Depends on how full you want this drum to get, but why not add a piece attached to the float going through the hole at the bottom and add a larger float say an inch or more below the float. Then as the water rises it starts to move the float up inside the tube before the water level get there.

Or just cut a bit of neoprene the same diameter of the float and stick it to the top of the float with super glue? Something elastomeric to help seal the float to the tube.

But I think you're over complicating it. Just tell the casual labourers "When water comes out of this hole turn off air - Drum is Full. Empty Drum. Then turn air back on again when drum is empty"

If they can't understand that then all hope is lost....



Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[3DDave]

Not sure the taper is so good an idea - the force will come from the vacuum - the sealing force is based on the area and the sealing pressure will be the force divided by the circumference*contact width. If the diameter doubles so does the sealing pressure. The float only needs to get close to the opening; the force supplied by buoyancy are likely negligible in comparison.

 

[moon161]

I think a heavier float would solve the problem. If you increase it's weight, it will be harder to suck up with the air, but don't increase it so much that it doesn't float in the pumped fluid and act as your stopper. Others have suggested this.