Dual and low pressure pumping for open systems
Last Post 30 Jun 2012 08:26 AM by Blake Clark. 4 Replies.
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Blake ClarkUser is Offline
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28 Jun 2012 07:48 PM
I've posted quite a few details about my system recently. Are there any regulars or lookie-loos who want details about low-pressure pumping and/or dual pressure pumping for open systems? I've got the data, the design and 2.5 years of trouble-free operation on a geo system that pumps at 20"hg vacuum. The same well pump supplies domestic use at 45 psi. One valve, one pump, simple controls. I'm happy to share. If no takers or everyone's reached their fill, I'll hang it up for awhile and let some other people have a turn.
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28 Jun 2012 11:50 PM
I'm interested

Does the 20" Hg derive from water falling back down the recharge well vertical discharge pipe? I've been wondering how the vacuum is maintained...what keeps air bubbles from migrating upward and breaking the vacuum? Is the line diameter reduced to ensure velocity of falling water exceeds bubbles' upward velocity. Is the vacuum broken during each off cycle?
Curt Kinder

The truth is incontrovertible. Malice may attack it, ignorance may deride it, but in the end, there it is - Winston Churchill

www.greenersolutionsair.com
Blake ClarkUser is Offline
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29 Jun 2012 09:08 AM
1 Vacuum is always created when water falls freely in a drop pipe. When operating, the full "pull" of my well-return line is about 26" Hg. When the flow stops, the pressure drops even further, down to the saturation pressure of water at discharge temperature.

2. The tail end of the drop pipe is usually submerged in my application. This is standing column, so I've had occasions where the water table dropped below then end of the pipe, exposing it to atmosphere. No significant change in system performance was noted other than losing siphon at the end of the cycle.

3. The tail-end of the discharge pipe is, by definition, at ambient pressure. Ambient pressure means nothing is going to get actively "sucked" up the pipe. However, since air is lighter than water, "bubbles" can "float" up the pipe. Flow velocity keeps most of them at bay, faster flow, fewer bubbles. **** There are two simple design solutions to eliminate bubbles altogether. For a below-surface discharge well, keep the drop pipe submerged below the water table. For a non-submerged surface discharge, rotate the end of the pipe so that it discharges straight up (like a fountain). ****

4.Coincidently, my discharge pipe does step down from 1 1/4" to 1" at the pitless adapter. But that was to get everything to fit down in the casing, not to keep the siphon. I doubt this is a crucial part of the design.

5. Since the tail-end of my pipe is submerged most of the time, vacuum is not lost at the end of the cycle. If my well level drops below the end of the pipe, the siphon is lost when the flow stops. I notice when this occurs it's easy enough to reestablish the siphon, but it takes quite awhile to completely flush all that air back out. Since losing siphon was rare in my case, this has not been an ongoing problem.

** If designing for a surface discharge, add at least a foot of vertical stand-pipe to the end of the run. Since air can't "float" in a downward direction, the standpipe should be enough to maintain siphon. **

You don't need much of an elevation change in the discharge pipe to get some big benefits. If tail end of your discharge line is only slightly below the unit, a matter of feet, it's possible to pump at 0 psi and still have all the flow you want.
jokinUser is Offline
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29 Jun 2012 01:08 PM
Very interested.  I just sent you a private message.

I am looking to learn more about this setup, to see if I could implement this.
Blake ClarkUser is Offline
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30 Jun 2012 08:26 AM
A couple people have PM'd me about their specific system. If anyone would like to post their system specifics (or plans), I'm happy to discuss conceptually how to adapt it to low or dual pressure pumping. "Low pressure" can be anything from "less than you're pumping now" to nearly full vacuum. The tradeoffs and costs within that range are significantly variable.

Compared to a typical pump and dump, the design and engineering for low pressure pumping is highly site-specific. There are too many variables to prescribe a one-size-fits all solution. One-size-fits all is why everyone is pumping at 40 PSI!. After the number crunching is done, though, the end result is much higher system efficiency with little added complexity to the pumping system.
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