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Design Reference for Low Pressure Pipe Onsite Wastewater Treatment System

Design Reference for Low Pressure Pipe Onsite Wastewater Treatment System

Design Reference for Low Pressure Pipe Onsite Wastewater Treatment System

(OP)
I am looking for any reference material on design of a low pressure pipe onsite wastewater treatment system. There is plenty of information available on the minimum standards, but I am having no luck finding hydraulic design information in relation to appropriately sizing the pump. We have designed several drip irrigation systems, but those use pressure compensating lines, so a larger pump simply wastes energy rather than an LPP system where a too large pump will overload the system.

RE: Design Reference for Low Pressure Pipe Onsite Wastewater Treatment System

The LPS systems that I am familiar with incorporate a semi-positive displacement pump.

The semi-positive displacement pump in the grinder pump station has a nearly vertical H-Q curve. This is the best type of pump for successful parallel operation of many pumps into a system of common low pressure mains. Since each pump will be located at a different point along common low pressure mains and at various elevations, each pump should operate in an efficient and predictable manner, whether one pump or numerous pumps are operating at a given moment; the pumps in such a system do not have a single fixed “operating point,” but must operate consistently over a wide range of heads that are
continually, and often rapidly, changing.

The E/One grinder pump has the capability of operating above the LPS system design criteria of 80 psig, or 185 feet (Figure 1). Based on the maximum daily number of pumps operating simultaneously (Table 3; see PDF) versus the number of pumps connected to the system at the design pressure of 185 feet, the capability to operate significantly above the system’s design pressure is mandatory in order for the system to operate properly during the approximately bimonthly peaks when the “absolute maximum” numbers of pumps are operating. This feature also ensures that pumping will continue under those conditions when higher–than–normal pressure occurs in the pipeline.

System designs with calculated heads approaching the upper limits of recommended heads should be reviewed by E/One application specialists. Contact your local E/One Regional Sales Office or authorized distributor for a no-cost, computerized review of your design. Occasionally during “normal” operation, there will be short periods when higher-than-design pressures will be experienced. These can result from a variety of causes including solids buildup (obstructions) or air bubbles.

Deposits of solids or air accumulation will be purged from the line since the pump continues to produce an essentially constant flow, even though the cross section of the pipeline has temporarily been reduced. Higher velocities through the reduced cross section will provide the scouring action needed to correct such conditions as soon as they start to appear.

These higher-than-expected pressure conditions are transitory occurrences. The only requirement is that no damage be done to the pumping equipment, pipelines or appurtenances during these occasional short periods. E/One grinder pumps are driven by motors rated for continuous operation at 104 F/40 C above ambient temperature. They can operate at 50 percent above rated pressure for at least 5 minutes without excessive temperature rise. Based on the Albany, New York, demonstration project, for this type of overload to last even as long as one minute would be rare.

http://www.eone.com/sewer-systems/regions/us/produ...

RE: Design Reference for Low Pressure Pipe Onsite Wastewater Treatment System

(OP)
BIMR, thanks for the reply. I reviewed the information, but it does not contain what we sought. Here are the system characteristics:

1050 lf ~ 2" sch 40 PVC dosing tank to field

3000 sq. ft. field (450 GPD per local ordinance, 0.15 loading rate)

Field is 10 lines, 5' O.C., 70 lf w/ # of, size, and spacing of distribution holes to be determined

There is 3' elevation difference from the lowest lateral to highest, we are only allowed 10% variance in lateral distribution.

Dosing amount is 5 to 10X's field lateral volume, pump will be set to operate for 322 gal per dose

Elevation head loss to field from pump ~ 15'

Friction head loss in supply pipe (initial assumption 30 GPM) ~ 18'

Desired operating pressure of field 3 psi ~ 7'

Hole spacing and size is used to distribute the pump head above 40' min. Its the hole spacing and size that we're stuck on, they can't be uniform through the field due to the elevation change between laterals when limited to 10% variation.

I completely understand why the boss said he quit designing these years back. Owners want residential systems designed for pennies and this is a very complex process compared to the alternatives.

RE: Design Reference for Low Pressure Pipe Onsite Wastewater Treatment System

I have an "old" E-one system design manual they used to freely publish perhaps 20 yrs ago, but I do not see the same documents published online today. There may be copyright issues with posting it online. You might try searching thru the professional engineering continuing education outfits ( eg, redvector.com)and take one of the online course that are focused on the LP wastewater systems.

"Whom the gods would destroy, they first make mad "

RE: Design Reference for Low Pressure Pipe Onsite Wastewater Treatment System

(OP)
Davefitz, thank you for the information on Red Vector. I have not used that site before, and will look through it. In the meantime, could you give me the title of your Design Manual (ISBN)? E-one has sections for Technical reprints, maybe I will be able to track it down through their website to download, or order it from a publisher.

RE: Design Reference for Low Pressure Pipe Onsite Wastewater Treatment System

Madcowscarnival,
I wrote a program for calculating LPP systems. I will do exactly what you are trying to accomplish. There is an automatic pump selection feature that is very helpful. You can also add pumps to the pump file.
I have been letting engineers use it for free. Take a look at www.squirtonsite.com
Tom

RE: Design Reference for Low Pressure Pipe Onsite Wastewater Treatment System

(OP)
Folks, thank you for the references. Years ago a local County had a publication very similar to the Orenco download, but nobody there recalls it or has been able to find it. Tkall, during this process I've been considering how useful it would be to setup a spreadsheet program to design one of these systems, but alas, free time is usually the most expensive. I will get working on that program, it looks similar to a program Geoflow provides for calculating pump sizes for their various drip systems. Most OWTS in my County are lagoons or drip systems, this will make a good lower cost alternative for some.

RE: Design Reference for Low Pressure Pipe Onsite Wastewater Treatment System

Madcowscarnival:
By all means take a look at Squirt I think you will like it. Maybe I'm ringing my own bell a little but I think you will find it very powerful and flexible. Here are a few videos to help you out:

Watch this one first http://squirtonsite.com/videos/squirtoverview.htm

Squirt Pump Selection http://www.youtube.com/watch?v=u5wEmSFoYBY

Adding Pumps http://www.youtube.com/watch?v=iC5CNC33V7w

Central Manifold http://www.youtube.com/watch?v=6064XQ-3q5o

Pitchfork Manifold http://www.youtube.com/watch?v=tzpNFMaNXa0

End Manifold http://www.youtube.com/watch?v=byCUGnAMquY

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