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Siphoning out pools


Well-known member
Came across this short video by pure chance today:


I wonder if such a thing could be scaled up to produce usable flow rates for us potholers trying to start siphons to lower sumps etc? (Looks like some sort of vertical lip would need to be created first though.)

Just musing . . .


Well-known member
Not sure up to what diameter it will work as the water is compressing the air in the tube & that suction is then dragging the water through.



Well-known member
This may be more practical (or then again it may not):

Another look at the self starter, can't find any examples larger than the straw:



Well-known member
Incidentally, ages ago I bought myself one of those tiny hosepipe pumps which you put in a drill chuck, in case it's ever useful with a cordless drill underground. Never got round to trying it for starting a siphon; must have a go some time. (Suspect it'll need to have water in the actual pump before it'll initiate a siphon.)

While I'm on, the disadvantage of using small bore pipes (such as hosepipes) is that it takes a long time, so your siphon may break before the follow up trip, allowing the pool or sump to refill. The trick to maintain the siphon is to have the outlet in a bucket, the rim of which is at a level just above where you want to siphon down to. The pool being siphoned will then come down to this level but the siphon is maintained, thus keeping the water at this level. (I was given this tip many years ago by ace digger Keith Bentham in Derbyshire and have used it very effectively many times since.)


Well-known member
The other end of the pipe also needs to stay in the water, & not be siphoning silt, as that will block the bucket end.

Another way to make it work would be to fix the pipe below the rim of the pool, so once pool filled the water would spill through the pipe rather than over the top, restarting the siphon. This only works where you don't have to lift the water any higher than the lip though. I guess if the pool hadn't refilled sufficiently to restart then lying in the water might raise the level enough!

Bob Mehew

Active member
There has been a siphon which has worked for much of the past 30 years in ANUS (Alt nan Uamh Stream) cave requiring only the occasional fettling.  It is based on a wide bore (over 1 inch from memory) pipe from pool to waste point being some 6 foot below the pool.  The waste point is in a bucket fed by a stream so the end of the syphon is always sealed.  The cunning bit is it uses a water aspirator (see https://en.wikipedia.org/wiki/Aspirator_(pump) ) to remake the siphon after it breaks.  The water aspirator is fed by a near by stream (which also feeds the waste bucket) and the air suction inlet is connected to the high point on the siphon pipe.  When the siphon breaks at the pool and then remakes, with both ends sealed, the aspirator sucks the air out sufficient to restart the siphon.  The aspirator was home made from pipe and rubber bungs and located so it had a reasonable head of water to drive it.  Keeping the water feed to the aspirator has been the least reliable bit.  It was made by a GSG member.

But I guess not all siphons are so conveniently close to a stream however.
Here is a reprint of the Earby Pump write up in Descent magazine which may be of interest
Stuart Whitmey. Earby P.C. Sec


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    EPC pump.jpg
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All of this seems a bit complicated.  If you have some kind of solid lip and nearby access to a point lower than the level you wish to drain to, it is easy to set up a siphon with a length of stiff wire and rag. Make a bundle of rag to fit the pipe fairly tightly, fixed to the end of the wire, the wire is pushed through the pipe to the lower end. Then submerge the other end in the pool to be drained and pull the rag through by the wire, this draws water over the lip and starts the siphon.

If you want to move the water longer distances, use a short length of pipe to start the siphon and once the siphon is started connect a longer length of pipe to the lower end. If you connect using a valve, then you can turn the siphon on and off. I used this decades ago on Snowdon with 2 inch alkathene pipe to supply a drilling rig with water from a flooded stope several hundred metres away. The siphon held overnight so in the morning we just had to turn the valve on. It really is quick and easy.



Well-known member
Couple of other ideas for getting it started:



Active member
loving this thread......we plan to make use of the water in and outside the caves in Nidderdale for helping us dig.....all useful stuff thanks folk

Duncan Price

Active member
Bob Smith said:
i'm a big fan of the self starting bell siphon,

Yup - me too.  we've got a big version in our waste water treatment plant at work which is used to measure how much water we put down the drains.  Every time the tank gets full the syphon kicks in and drains it.  There's a flow meter on the outlet which counts drain cycles.  Its more complicated that the one shown in the video (http://www.americanonsite.com/american/catalog/am-autosiph.html - we made ours out of pits of PVC pipe solvent welded together).

There were (still are) several hosepipes in Elm hole which were used to drain the two ducks into Sump 1 and 2 to make getting to Sump 2 (the one which goes into the main drain to Daren Cilau).  When we were digging open the choke to Pwll-y-Cwm I would take diving cylinders into the cave on a Friday evening and to the syphons going for a trip later in the weekend.