Siphon Break Question

[sshep]

Friends,

We have periodic and cyclic episodes of overflow from a condensate drum with a funny looking siphon break. For some reason we did not tie-into the top of the lute, but instead on the side below the the drum liquid level. Lowering the level within the small allowable range does not seem to stop the overflow. The pressure in the drum appears to be fine, although a better pressure survey is the other cause I am checking in the event of excess back pressure on the drum.

I have been assured that the siphon break should work as designed, but I have my doubts. Check my sketch and let me know if this can really work.

best wishes,
sshep

 

[sshep]

I am still learning, so try this file:

 

[StoneCold]

sshep
My guess would be no, it will not work because water backs up into the line before it goes over the top.
Have you tried just taking off the blind flange at the top of the drain or drilling a 1/2" hole in the top of the elbow of the drain?
I would guess that very little pressure in the top of the drum, caused by condensed liquid in the air cooler would force liquid out the drain continuously as well.
In real life is the 180 elbow in the drain significantly higher than the liquid level control?

Regards
StoneCold

 

[CJKruger]

sshep, I think the vent line can only break the siphon once the level drops below the vent line tie point.

1) So, overflow will start when the drum water level is above the 180 bend, and stop when the level drop below the vent tie point.

2) This assumes the overflow pipe is fairly small. If the overflow pipe is large (self venting flow) and not sealed in water at the bottom, then there should be no siphoning.

 

[katmar]

I would expect this arrangement to prevent the drum from ever being siphoned completely empty, but I would expect cyclical behavior.

If the level in the drum rose to the point where the head in the drum (i.e. level plus vapor space pressure) was greater than the height of the apex of the lute then condensate would flow out through the lute. If this flow rate was sufficient to fill the downleg of the lute then a siphon would be established. The siphon would continue to flow until the head in the drum was less than the height of the side entry to the lute. At this point air would be drawn in by the siphon, and the siphon would break. The tank level (or head) would have to increase all the way up to the apex of the lute before the siphon could be re-established.

In this way I would expect the tank level to cycle up and down between the height of the side entry and the apex of the lute, but never to go all the way down to zero.

Katmar Software
Engineering & Risk Analysis Software

http://katmarsoftware.com

 

[bimr]

One would think that the tank is under 5 psig of pressure. That would require a loop seal of 11.5 feet.

The connection to the loop seal should not be on the pump suction line. The pump may be draining the loop seal and pullimg air into the pump.

I don't see how this arrangement will function.

 

[athomas236]

sshep,

I agree with what katmar says about about establishing the siphon and flow with increasing drum level but consider that the siphon and flow will cease to function under falling level conditions when the level reaches the top of the inverted "U". Not convinced that the level of the side entry pipe has any impact.

Regards,

athomas236

 

[katmar]

athomas236, if the siphon does get established (i.e. downflow pipe is not sized for self venting flow - see CJKruger's post above) it can only be "killed" when it is easier for the siphon to suck in air than it is to suck water from the drum. This point occurs when the level (or rather the head) in the drum reaches the head equivalent to the height of the side entry pipe.

Katmar Software
Engineering & Risk Analysis Software

http://katmarsoftware.com

 

[athomas236]

katmar,

I understand now, thanks.

Regards,

athomas236

 

[ajs1972]

Hello Katmar:

You are right, in fact this is the base of design in vacuum condenser systems. The height of the leg is designed to 10 meters, in order to achieve the maximum vacuum in the condenser and to avoid the flooding.