What would you call this PVC "loop" / "horseshoe" thing?

[Chiperific]

Hi, turning to the pros for help finding a good descriptive name for this 1/2-inch PVC horse-shoe-like fixture.

This is a 3-stage water filter that my organization developed for use in rural communities in the developing world. It's made from common PVC components, two 5 gallon buckets, and a 3-inch 0.1-micron hollow-fiber membrane filter cartridge.

In the top bucket, we use a few inches of sifted and washed sand as a pre-filter to remove sediment, turbidity, etc.

The "half-loop" of 1/2-inch SCH 40 PVC has a few purposes:

1. It has three 1/16" holes drilled in the end cap to allow water to enter the system. (and a 50-mesh metal disk inside to keep the sand from entering the system). This ensures the water has first filtered through the sand bed.
2. The height of the pipes sets a water level that keeps the sand underwater, which keeps the water channels open, and prevents mud and clay from drying and hardening on the top of the sand.
3. The male adapter passes through the bottom of the bucket and lid (a make-shift bulkhead fitting) to transfer water to the lower bucket.

We've been calling this the "sand pre-filter", but that's a terrible name. The *sand* is the pre-filter.
This PVC component is some sort of reverse-trap, or ant-siphon, or elongated bulkhead ...

We need a better, more aptly descriptive name for it. What would you call this thing?

More pics attached.

Thanks in advance.

- Chip

P.S., the organization is: https://20liters.org if you wanna see more about the filter itself.

 

[LLigetfa]

This PVC component is some sort of reverse-trap...

It is a trap weir.

 

[Sponsor]

 

[Chiperific]

It is a trap weir.

Ok, yeah, I can see that. Kudos for technical terms!
However, is this really a trap? It's not filled with water to block air. Only the right-side leg with the drilled end-cap would have any standing water once the water level drops below the horizontal pipe.

Is there anything that would better describe its purpose in holding the water level at a specific height?

 

[wwhitney]

Sorry, why doesn't the "u-thingie" cause the upper bucket to siphon? What happens when you let both buckets get completely full, and then open the bottom stopcock wide open?

Is it somehow always keeping air trapped in it, so it can never fill with water? Or perhaps there a rate effect, where the outlet leg of the U can let out water so much faster than the holes and the screen can let it in?

As for name, function #2 is the key feature that determines its shape. So how about outflow limiter or outflow level limiter or something like that?

Cheers, Wayne

 

[Chiperific]

Sorry, why doesn't the "u-thingie" cause the upper bucket to siphon? What happens when you let both buckets get completely full, and then open the bottom stopcock wide open?

Is it somehow always keeping air trapped in it, so it can never fill with water? Or perhaps there a rate effect, where the outlet leg of the U can let out water so much faster than the holes and the screen can let it in?

The flow rate through the sand is slow enough that it never fills the whole volume of the 1/2" pipe with water (no slug). The flow to the bottom bucket is a small stream at best. So the water just stops at the bottom of the ID of the horizontal pipe.

Yes, the outlet way out-paces the inlet, mostly because of the resistance caused by the sand (more than the 3x 1/16" holes).

What happens when you let both buckets get completely full, and then open the bottom stopcock wide open?

The 0.1-micron filter is incredibly dense. Having the maximum pressure of a full bottom bucket gives you a steady thread of water through the faucet. In fact, there's no flow at all until the bucket is at least 1/3 full.

We use un-gasketed lids so there's not an air seal in the bottom bucket. You can theoretically overflow the bottom bucket, but we train end-users on the capacity. Most users leave the faucet open and collect the filtered water into a jerrycan.

We've experimented with sealing the bottom bucket, but it ultimately stops the water flow when the pressures equalize. It is handy for preventing over-filling, and adding a bit of pressure, but it really reduces the overall thru-put of the system (just over 100 liters of water in about a 14-hour period).

As for name, function #2 is the key feature that determines its shape. So how about outflow limiter or outflow level limiter or something like that?

I like these! (I also kinda like "u-thingie", though)

Thanks!

 

[LLigetfa]

However, is this really a trap?

Yes it is. Compare it to a toilet.

 

[Chiperific]

Yes it is. Compare it to a toilet.

Ok, I see it now!

 

[wwhitney]

But trap weir would refer to a particular part/elevation of the u-thingie, not the overall u-thingie.

I guess you could also call the u-thingie an air trap. It's designed to stay full of air, and not to let the air level in the upper bucket get too low. Just like a normal water trap is designed to stay full of water, and not to let the water level get too high (absent a blockage, water above the trap weir will drain.) Up and down being reversed in this analogy, as air is lighter than water.

Cheers, Wayne

 

[Chiperific]

But trap weir would refer to a particular part/elevation of the u-thingie, not the overall u-thingie.

Agreed, the whole thing could be described a "trap", but it feels reversed/upsidedown from a usual trap.

I get that there is a weir function and the trapway in the toilet is a great visual comparison (to @LLigetfa 's credit).

I guess you could also call the u-thingie an air trap. It's designed to stay full of air, and not to let the air level in the upper bucket get too low. Just like a normal water trap is designed to stay full of water, and not to let the water level get too high (absent a blockage, water above the trap weir will drain.) Up and down being reversed in this analogy, as air is lighter than water.

Yeah, "air trap" does make more sense, I just have a hard time wrapping my brain around this as an air system instead of a water system.

Outside of its weir function, I'm thinking to focus more on its functionality as a transfer between stage 2 and stage 3.

"transfer trap", "outflow loop", "sand bed drain"...

 

[LLigetfa]

I get that there is a weir function and the trapway in the toilet is a great visual comparison (to @LLigetfa 's credit).

Borrow from the toilet example and call it a "trapway".