air bubble in 6" pipe

[redroot]

I have installed a stream engine, manufactured be Energy Systems, And Design.

It is a pond based siphon system, ie: the intake (a pvc 6" pipe) is submerged underwater, and the pipe goes out of the pond over the berm, then travels 160' (run),

to the turbine, Max head of 15'.  

I am moving a max of 150 gpm at 6.5 psi.

The problem: an air bubble is developing at the top of the berm.

The solution?

1. is there a cheap (hand) automotive vacuum pump out there to suck the air bubble out?
   
2. other pumps which could suck that air bubble out?
   
   

I am fairly convident that my plumbing is tight, but there is a possibility that I will have to always deal with air bubble, so I looking for a long term effective solution.

thoughts appreciated,

darryl

[willib]

How can you see the air bubble?

is the tubing clear?

a possible solution is to ,every once in a while , let the water go full blast and suck the air bubble down the pipe..

[vawtman]

When you say over the berm does the pipe stay at least level or uphill from there?If it slopes down.You will have air problems.

[jimovonz]

Why not dig the pipe into the 'berm' so that there is fall all the way? The suction height reduces the effective head anyway. Its not an easy thing to setup a siphon in a 6" diameter line as the water in the pipe requires momentum to get over the hump - otherwise it just falls back...

[nothing to lose]

I think you need to figure out why the air bubble is there and how to stop it from comming back again. A correct siphon should not have an airbubble in the line, so something is not right, but I am sure you realize that. If all your joints are sealed, then perhaps the water is not keeping the pipe full enough, flowing fast enough, from the end and letting air seep back in? Maybe you just did not get all the air out to begin with and it slowly craweled up hill to the highest point, fighting the water flow of the other direction. Sometimes that happens, many smaller bubbles in a line gather at the highest point. I never did a big siphon like yours but in moving liquids I use normal siphons and hoses alot. 15' drop for 160' of pipe does not seem like alot, depending how it lays, if the end is level or has the drop etc.. I would think perhaps the air is entering from the outlet. If that is the case then maybe making the end just a bit smaller would stop the problem, maybe cap the 6" pipe to only 5.5" opening. How did you measure and where, the PSI as 6.5?

 Any air compressor can basically be used as a vacum pump also, just connect to the air inlet and you have suction. How to do this varies with compressor design. I think you could mod one of those little 12V car tire compressors that plug into a cigerrette lighter easy enough. Your not wanting to draw a large vacum, just remove standing air so it should work good for that. The thing about compressors used this way is the piston is made to work hard compressing air, not sucking air, so if you were trying to draw a heavy vacume you could shatter the piston, even in large heavy duty compressors same thing. Just to remove air though it should work fine.

If you have a junk fridge or freezer handy and power available many people use the compressors from those for vacum pump also.

Got a shop VAC? Preferrably a wet dry type

As for a hand pump? Whats that

 I have not used one of those for years for anything but ballons when making twisty animals. If you have one or can find a cheap one to buy, find where it sucks in the air, you should be able to install a fitting in the hole and attach a hose. I remember one I had years ago that had a small hole in the top cap where it sucked in the air, close to the shaft.

Also I have no idea how much air you need to remove or how you will connect the vacum pump etc.., but perhaps one of those small airpumps for the ballons would also work?

 Wall-mart (and other places) were selling about a dozen twisty balloons and a small air pump for $2. Get rid of the air bubble and get a new hobby at the same time

 For $2 the ballons are ok, the pump was decent, and it comes with a small book how to twist several animals like a poodle. I don't have one handy to look at, but I think the pump could easily  been modded to suck a small vacum, just plastic so it's easy to put a hole anywhere and connect a hose. All my Clown and Magic stuff is put away or I would take a lok at one. I know I used my professional ballon pump for a vacum a couple times, the $2 ones are just a much smaller cheaper version really so should also work.

 I was giving away those $2 sets, I think they were in the toy section of the store, not the party section. I used to buy them by the dozens. Probably the only thing I could never find a wholesaler for

[redroot]

yA THANKS,

i would like to see the price tag on that one!

I have been able to run the siphon with out the air bubble developing, so it seems to be a tempermental issue (or perhaps temperature).

I would be interested in the physics of losing the head by having to raise the water over the berm.

here are some numbers:

6. " pipe (pvc)
   
150. gpm
     
     

approx. 6 to 6.5 psi

from water level to top of berm 1.5 feet

how much head am I losing?

darryl

[redroot]

well if I understand you correctly,

the pipe exists the pond water level, needs to go about 2.5', and rise 1.5', then a 22 degree elbow to follow along the top of berm, the pipe at this point falls slightly downhill, not much 1/4 per foot, then elbow again another 22 degrees, and falls downhill towards the turbine.

is this the source of the problem?

darryl

[redroot]

no the pipe is not clear,

I can knock on the pipe and hear a distinctive "hollow sound air".

along with this I can hear some turbulence.

[redroot]

great suggestions, however I have an aversion to Wal-mart, although i like ballons.

I have been able to run the siphon for several days without the air bubble happening.

so it seems to be something that develops under certain conditions, and I would like to resolve what ecaxctly those are, but at this point i am interested in the vacuum pump idea, so thanks for all the suggestions, i will try one or many.

[cyplesma]

If you have access to a walmart or kmart or something similiar check the water sporting section (beach balls and such) they have a big red pump that has a air suck and an air blow tube.

it comes with a black plastic hose about 2 foot long.

now if this just started probably take some sealant and just glob the sealant around all the seams above water level.

or... for a really fancy long term solution.......  

find a water bed burper. find a way to mount it at top of the air bubble with top section mounted to the IN tube of above air pump.

when the air forms at top simple draw it out through the waterbed burper with the air pump. like drawing fluid into a needle.

the water bed burper is a one way valve to let air out of a water bed without letting air back in.

sorry if it's a little too gadgety, just happen to be watching modern marvels gadget episode.

[harrie]

Hi redroot. Maybe you have a muskrat going in the pipe and temporary blocking it allowing air to feed back up the pipe. Ha. Just a thought.

Great fun, Harrie

[wpowokal]

Redroot, high volume low head pumps sometimes have a hand operated diaphram pump for priming, simply a diaphram and two valves.

IMHO this would overcome your problem, as someone else said the air could well be entering at the discharge. Does it discharge underwater?

How deep is the suction submerged? Is there a possibility of a vortex developing thus that air enters. A suction strainer can eliminate this by spreading the water entry points out.

A crude solution is to fit an air relief valve at the highest point, and periodically shut the discharge.

allan down under

[Nando]

The pond itself can be the culprit, gases generate in the bottom, commonly occurrence.

Enough air there may break the siphon effect.

If I believe I am right, this is what I remember with one siphon that had air bubbles problems: Drill a hole on top of the highest point of the siphon, where the air may be collected, then take a small pipe (1/2 diameter or so) and make a siphon with a T at the apex, place the end of the siphon intake close to the 6 inch intake, the other side (the exit), the one going down hill at least 3 or 4 feet below the intake level, then connect the third part of the T to the hole you made to the 6 inch pipe, BUT install a valve to close or barely open it to allow sucking the air out of the 6 inch. Add another valve to close the 1/2 inch siphon.

A possible simpler way, is to make a manual sucker.

One way valve (out) on the apex of the 6 inch siphon,to a T and one side going to another one way valve (out) then the third end going to a larger pipe that has a piston in it, One pulls the piston to extract the air out of the pipe, push to expel the air out to the piston chamber -- so pull - push several times to remove all the air from the pipe.

There is another way and is to have a raiser at the beginning of the intake pipe to allow the air to accumulate there instead of the apex, then periodically the top of the raiser that has a valve is opened to allow the air to scape, since the siphon is working and the raiser is still under water no siphon effect is lost. it can be done automatically with a float inside the raiser that opens the hole to allow the air ot escape.

Nando

[whirlybird]

Well I feel  that I should add my 10 cents worth here.

It seems to me that you have one of the classic problems that all of us in the pumping industry have encountered many times in the past.

If the siphon outlet is the same size as the intake you will get cavitation and therefore separation in the water column. Best practice is to install a quick shutoff valve about 1 yard or a meter below the pond water level on the outlet pipe( don't put it at the discharge point as this will cause catastrophic water hammer) then add a small one way valve at the highest point in the pipe, Shut the valve and you should hear the air bleeding out you may need to do this several times. Or until water exits the valve.

If the inlet and outlet are constantly submerged the problem will not reoccur.

Good luck.

Whirlybird

PS reduce the outlet diameter to less than the inlet.

Have fun.

[wdyasq]

Darryl,

I built and maintained several large siphons years ago.  I used a hand bilge pump that had a connection to the pump so I could pull a partial vacuum at the peak of the siphon. I had a small 'ball valve' so I could use the same pump on several siphons. It was similar to some here:

http://tinyurl.com/8jryk

One of the daily chores was to restart or remove the 'air pocket' that seemed to always appear in the top of the siphon.  I always figured it was dissolved gasses the separated from the water.  The siphons that started deeper in the water would fail or slow first. On the particular project, we were pumping from a 'hole' below the dam and had a few hours if one of the siphons slowed or stopped.  

Ron

[Vtbsr]

If you could get a 4 hp honda water pump tapped into the botton end of the pentstock with a valve. Shut off the bottom main valve and pump water up the penstock over the hump. Try to restrict the flow at the top end so the water does not run right out. When you don't see any bubbles, remove the top obstruction and open the bottom valve and let her rip. I would try to keep the inlet 3 feet below the surface to stop any vortecs  from forming and letting in air. I would try to dig the pipe down level so you don't have to have to keep playing around with the problem. good luck

[vawtman]

I work on installing and maintaining pumps.For horizontle runs the pipe should be level or slightly uphill.Any up then down piping will create air at the high point.Im talking on the suction side.

[redroot]

this sounds great, just check it out and it might work.

the question is does it have enough "suck" to overcome the weight/velocity of water?

Im o.k with the daily task, as the pond is easy access.  I am still trying to understand the physics involved.  Any thoughts?

love simple solutions:

[redroot]

sounds interesting, will it work while the siphon is operating and the water is under suction?

I have never seen or used on, so let me know if you have used it under the above conditions.

thanks

[redroot]

"manual sucker"

I could go with this idea, but here's my hesitation:

I am dealing with 6" pipe, and the cost just keeps going up, but than so is gas!

I have been having problems finding some 6" pvc fittings, (like a swing type check valve) so do you know if finding a 6" one way valve is going to hard, or where the swing type valve can be bought.

the piston should be easy to manufacture, but will it be strong enough?  I have asked elsewhere; what is the physics envolved?  and how powerful does the suction need to be?

I am sucker till I get this hydro system working!

[wpowokal]

Er perhaps I miss understand but if you refer to an air purge point, by manual pump or what ever.

You do not need a 6" fitting, this pipe is under vacume, a 1/2" hole drilled in the highest point areldite/selastic a 1/2" fitting to that and connect a diaphram pump, OR!

I believe one reply touched on the most simple solution, but for the little its worth, I will continue.

Glue a 1/2" fitting to the highest point, about 30' down the line glue another. Glue a 1/4" tube into both fittings making sure the down one extends some inches into the pipe.

The air from the highest point will be entrained into the downstreem flow.

allan down under

[wdyasq]

Darryl,

The way a siphon works is the pressure of water on the downhill side is greater than the lift on the uphill side.  The highest point and lowest pressure point is your air-bubble.

There is no 'weight' or 'velocity' of your 'air-bubble', it is a partial vacuum. You need to remove what air is in there.  If it were me - but it isn't, I would get a section of bell, coupler or part of a discarded 'joint', cut a section to make a doubler', glue it to the area the bubble is, let the glue set then drill and tap for a fitting (put a check valve here).  Remove the offending bubble. This same tap would be necessary for Allan's excellent advice of making a vacuum venturi and let it be self servicing. You may have an existing fitting in the proper place you can drill and tap.

A near perfect vacuum is over 30' of water. It is fairly simple to pull 15' of water. If one realy wanted to get fancy they could put a small wind-mill on the berm and power a little piston or diaphram pump with it.

Ron

[Nando]

THIS IDEA IA OK AS WELL.

My cousin used it several times, when the water source had air that accumulated in the apex of the siphon.

The hole was drilled and tapped to insert a brass coupling 1/4 inch in a 8 inch pipe siphon, then using a half inch pipe connected to the coupling and the pipe was brought down to about 2 meters head and another hole was drilled, in this case a 1/2 inch to terminate the pipe, this way the air is brought down by the pulling generated by the height differential of the 1/2 pipe length.

A small valve was installed next to the upper brass coupling to regulate the system, the adjustment was minimal opening, all depending on the air volume that was accumulating in the apex, also he installed a small section of transparent pipe to see the bubbles passing by to know what to do.

Nando

[redroot]

Hey Ron, Nando, and Allan down  under,

thanks for the replies.

this is new to me, so I am having problems following what people are actually saying.

I drill a hole into the 6" pipe at highest point, than stick a new pipe say 1/2" (call it a riser) into 6" and just glue the "sucker" in there?  No 6" fittings like a  6" to 1/2 tee?

Next I do this somewhere down the line, same deal with glueing, but this riser goes a little deeper into the 6" pipe?

How high should the risers be?

and the valves.  Where excactly do they, (or is it just one) go?  And is it a check valve?  

a little more help for me, seems as though I cant quite grasp the concept, therefore cant visulize how to do it.

slow learner, but going with the flow,

thanks

[wpowokal]

Darryl, Height is not the objective just glue the sucker in, the downstreem one is a few inches into the pipe to  create a venturie effect.

http://www.ce.utexas.edu/prof/kinnas/319LAB/Applets/Venturi/venturi.html

http://www.efunda.com/formulae/fluids/venturi_flowmeter.cfm

You are not exactly replicating one just creating the effect.

The valves are for isolating if necessary and as suggested throttling the upstreem one may/will enhance the effect.

allan down under