55 Gallon Drum for lift bag

[PvilleStang]

Does anyone know of a good site for DIY directions? I need to put in an air bleeder at the bottom (top) of the barrel so I can bleed air out while lifting. I could do this if it was an open top barrel, but since it's a closed plastic barrel, I can't really figure out a way to get the valve fastened tightly without taking off the top somehow. Thanks ahead of time.

PvilleStang

 

[Thalassamania]

Personally, I would not use anything that is significantly negative to construct a lift bag, so I 'm glad you are planning to use a plastic drum. There are a fair number of PVC plumbing fittings that will serve your needs.

 

[fire_diver]

Why not cut the top off, and cut strap mounting holes along the rim? Turn it upside down and you now have an open bottom liffting device. You can even install you bleeder valve if you still need it.

 

[HowardE]

Umm... Why would you do this rather than just buy a properly functioning lift bag? this seems kind of dangerous. Having done some large lifts and worked with lifting 55 gallon drums as well... they aren't that stable.

 

[Thalassamania]

Agreed, they tend to be ungainly and are easy, as they surface, to tip and spill air out of.

 

[Codiak]

get a replacement drain plug for a cooler

 

[PvilleStang]

The reasoning behind not cutting open the bottom is for the tip over factor and stability. And the bleeder valve allows for adjustments when the barrel gains buoyancy with depth change. I believe with using the original bung holes the attachment point will be stable enough, but if you cut open the top, you take away from the structural stability, especially if using holes made in the sides rather than on the top. Now, here's the interesting part with my devious plan. When not in use, these barrels will likely double as rain barrels, so I'm trying to find a bleeder valve that will attach to a standard garden hose.

 

[Delta_P]

How heavy and how deep is the item you're planning on lifting?

Am I understanding correctly that you're planning to ride a 55 gallon drum to the surface during a lift, feathering the drum's buoyancy on the way up?

 

[Lobzilla]

My first thought was "crazy idea" but the rigid drum actually opens the door to a nice feature.

What is the big nuisance with a soft lift bag? Expanding gas volume and the resulting increase in buoyancy. Not a big problem if we want to send something to the surface. But if we want to relocate a heavy object underwater, that expansion is going to make our life really miserable. It creates an unstable equilibrium that we have to fight with venting and addition of gas.

Now, picture a water-filled drum, underwater, with the two holes facing down. One hole is closed or has a one way valve for injecting gas. The other hole is sealed with a pipe that goes up into the drum to, let's say, half of the height. The end of this 'standpipe' outside of the drum is open.

If we would fill this drum with gas until the gas comes out of the standpipe the buoyancy (approx. 220 lbs in this example) would remain constant on the way up. Any increase in gas volume due to expansion would just vent out of the standpipe. Bingo - constant buoyancy lift 'bag'. (At least on the way up. When going back down, we would have to add gas to compensate for the compression.)

If we make the standpipe sliding in a bung fitting we can adjust the buoyancy to any amount we wish.

 

[HowardE]

If you're dead set on using a 55 gallon drum I would suggest you use a plastic one first off... then

2) don't make it open bottom. Use it like a salvage tube, and not like an open bottom bag. Put a blow off valve on the side bung hole, and keep it pointing down (this will let the water dump out when you fill it with air).
3) have an air inlet valve on one end, and another opv on the other.
4) fill it with water so that its neutral until you fill it with air.

Don't ride it to the surface.