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Vacuum when pump shut off

Vacuum when pump shut off

Vacuum when pump shut off

(OP)
My father has an interesting problem I thought someone here might have some insight into. He has a home heating system that pumps non-potable groundwater through a heat pump for heat. The problem is that it ices over sometimes due to a slight leak in the drain cutoff valve. I have an idea to prevent it but need a little help on the math.

The drain after the exchanger and cutoff valve is a horizontal run of about 20', a rise of 6", a slight down slope for the 10" as it goes through the wall, and a vertical drop of about 3' before it empties into a larger drain out to the drain field. At a cycle end, a soft-closing valve (so no water hammer) shuts, and the exterior portion of the pipe drains and all is well. However, the valve tends to leak, and if the water dribbles out of the exterior portion, the section through the wall freezes up in cold weather.

He's looking for a way to drop the level behind the high point by a couple of inches on cycle end so that a small leak in the valve won't dribble water into the external run. It's about a 50% duty cycle during the coldest weather, so it doesn't have to drop it much.

My thought was to put a check valve at the bottom of the 6" vertical section just inside of the wall. That check valve would draw air into that section just as the valve closes and the exterior vertical section empties creating a temporary suction. That check valve would have to draw air from outside, since if the drain does still freeze over or gets blocked for some reason, and the check valve fails under pressure, we don't want it spraying water inside. Plus he would want a long enough run that the air approaches room temp before it hits the check valve so that it doesn't freeze inside too.

My questions: Will it work? And will that 3' of vertical pipe produce enough vacuum to pull in sufficient air? My research tells me it will start at about .1mil, decreasing as it drains, but this isn't exactly my field. Thoughts?

RE: Vacuum when pump shut off

Sorry, I realize this is in front of you and you have described it well, but really a simple sketch with dimensions and heights and what you intend to do would be much much easier to understand. Also why don't you just fix the leaking valve?

Look forward to seeing the drawing so I can follow the piping layout .

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Vacuum when pump shut off

It is not going to work. Check valves will not function with such a low pressure differential.

Why don't you just fix the leaky valve. Another alternative is heat tape.

RE: Vacuum when pump shut off

Ok, had a spare mnute so drew it out. what you need is a vacuum valve with a float. Something like this http://www.valmatic.com/airvacuumWW.html

located on your 20 foot bit of pipe.

It won't drain too much out before it sucks air through the syphon so place it as close to the valve end as you can.

You can normally get them to attach a pipe to the inlet vent so that if it does fail then you can pipe the open end somewhere else.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Vacuum when pump shut off

LittleInch, one thinks the objective here is to save a nickel.

RE: Vacuum when pump shut off

Ummmmm, maybe. Replace/repair the valve seems a better idea alright.....

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Vacuum when pump shut off

(OP)
Thanks for your response, guys. Sorry it's taken me a few days to get back to you.

@bimr, he's tried that. New valves work for a while, but inevitably start leaking again. During the winter months, the electrically operated valve has to open and close every few minutes so it may be duty-cycle related...

@LittleInch, that's interesting and looks like just what I had in mind. I'll suggest that to him. Any tips as to what height the top of the float would need to be in relation to the output line's crest? Just below?

He's leaning towards an alternate solution that just opens another valve close to the source for a couple seconds after the cycle ends to drain some of the standing water backwards and into a floor drain. In thinking about that, he would have to wait a couple of seconds while the external vertical section stops gurgling or else he may just draw in air at the new valve. He's from the motor and relay generation, whereas my thought was a micro-controller would be just the ticket. Of course, then you have yet another valve that may leak, but at least that would just drip into the floor drain...

Thanks again!

RE: Vacuum when pump shut off

A few more thoughts:

Don't know the volume of water, but it may be possible to use a condensate pump or sump pump:

http://www.amazon.com/s?ie=UTF8&page=1&rh=...

Another alternative is to drain to either the sewer or to the foundation drain sump. If you have a foundation drain, it will pump the water out to the yard.

RE: Vacuum when pump shut off

Petie,

Yes you need to be at a level where the water will activate the float.

If you have the ability to add another valve then you could immediately open a valve close to the main one on the drain line as soon as the drain valve shuts, for say 10 or 15 seconds then closes again. This way you can seal in the drain line.

It all depends on the velocity of the water in the drain line IMO. You could easily trial this by installing a manual valve and then open the valve as soon as the drain valve closes to see if it sweeps enough water out?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

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