Pressure Distribution. Western Canada Onsite Wastewater Management Association

Transcription

1 Pressure Distribution

2 EFFLUENT DISTRIBUTION Get even distribution Space the doses Layout the distribution system Make choices for: piping, orifices, volumes Use worksheets for calculations

3 Dose or flush is needed for distribution Requires designed GPM and designed head pressure. What are the benefits of a dosed volume over a trickle? What effect does cold weather have on a system? Do you have any control over trickle distribution?

4 What is the main objective when distributing effluent, whether by gravity or pressure? Even distribution of effluent throughout the field or mound.

5 Why is a well designed pressure distribution system better than a gravity one, for the soil component? Pressure distribution provides more uniform distribution. Soil organisms are fed evenly in unsaturated flow condition. Gravity is more simple, but more affected by construction tolerances (ie. Water always flows to the low spot). Gravity can overload the beginning of the trench, which causes saturated flow through the basal area.

6 Types of Distribution

7 Total Gravity Distribution Siphon / pump provides dosed amount to field bed. Flows by gravity through distribution boxes, gravity pipe header, or drop boxes. Can be used in Type 1 effluent fields only.

8 Total Pressure Distribution Pressurized header & laterals. Can be used in any soil base treatment. Must be used for mounds, sand filters & the new at-grade system Distribution on sand filter

9 DOSING Demand or Timed?

10 ON-DEMAND DOSING Discharges as wastewater is generated. Potential for re-dosing before field can absorb last dose of effluent, especially during high peak flow periods.

11 TIMED DOSING Timer controlled pump. Peak or high flow surges are controlled with a High Water Alarm and Timer over-ride. Better for field operation allows for dosing during off-peak times (night). When does peak flow occur? Requires larger dosing chamber.

12 SITE ELEVATION Elevation changes between laterals, and orifices can change discharge rates from orifices. Topography Matters: The higher the head, the higher the flows therefore, lower laterals in the field deliver more effluent than high laterals.

13 SQUIRT HEIGHT 3/16 or larger orifice size requires a 3 foot squirt height. 1/8 and 5/32 orifices require a squirt height of 5 feet. Residual pressure (squirt height) at orifices must be measured. A variation of 20% in squirt height = an approximate discharge rage of 10%

14 SQUIRT HEIGHT Considerations: There should not be large differences throughout the field. When checking pressure, watch the time that it takes for liquid to get from the first orifice to the last orifice when discharging. Implications: Small, short laterals. Small diameter pipe with evenly spaced orifices. Cleanouts should be installed at the end of each lateral.

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16 ORIFICES Should orifices point up or down? What should you consider? What kind of pipe can be used? ABS DWV NO! PVC Pipe, Sched. 40 or Series 160 or 200? Pipe must be smooth, rigid, plastic piping. Should pipe be laying on sand layer of mound or on the trench bottom or held up? How do you support pipe, and what spacing should you use for supports? 4 feet max. - CSA Standard

17 ORIFICES Are orifice shields necessary? What do orifice shields do? What kind are available? Where do you get orifice shields.

18 DOSING VOLUME Overview: Smaller is better, to a point if doses are too small, the effluent won t reach the far end of laterals. Dose volume should be a maximum of 20% of the expected average volume/day for fields and mounds. Use approximately 5X volume of distribution lateral network piping. In large fields, an option is to divide laterals into separate zones to minimize dose volume (and pump size).

19 FITTINGS & FRICTION LOSS

20 DISTRIBUTION HEADER LAYOUT What will improve performance? What things create uneven distribution? Did dose volumes work effectively on each lateral layout?

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22 Distribution Lateral Sizes: p. 17 to 21 of 24, PD Worksheet, SPM Appendices Orifice Discharge Rates: p. 13 of 24, PD Worksheet, SPM Appendices Pressure Loss through Piping: p. 14 of 24, PD Worksheet, SPM Appendices Volume in Pipe: p. 16 of 24, PD Worksheet, SPM Appendices

23 DIAMETER OF LATERALS P. 22 & 23 of 24. What diameter of lateral is needed for A 60 long lateral, with 16 x 1/8 orifices. A 48 long lateral, with 20 x 5/32 orifices. We pick the number of orifices.

24 # OF ORIFICES & SIZE OF LATERAL How many orifices can be in a ¾ pipe, 60 feet long? How many orifices can be in an 1 ¼ pipe, 60 feet long? What typically happens with end-fed laterals? What happens when changed to centre-fed? Table A.1.A

25 SQUIRT HEIGHT Discharge rate changes with squirt height. What discharge difference is there between a 1/8 orifice at 3 and 6? What differences would you see on the laterals at different elevations? What can you do to achieve even squirt height on laterals with varying elevations?

26 ORIFICE DISCHARGE P. 13 of 24, PD Worksheet, SPM Appendices. What is discharged from a ¼ orifice at 5 squirt? If you have 40 orifices, what is the total discharge? How will your choices of orifice size affect the system requirements?

27 How will your choice of orifice size and delivery pipe size affect system pumping requirements? Orifice size and spacing affects the volume required for a total system. What size of pump is required by the system? Should you design for a particular pump or just design and then buy the pump? Or both? Desired spacing on a mound is one orifice per each 4sq. ft. of sand. If 24 or less wide, chamber is used. In pipe and rock bed, 1 orifice per 6 sq.ft. of sand mound area. Stagger orifices for better coverage.

28 DELIVERY PIPE FRICTION LOSS Measure from pump to far end of distribution header. Volume used is amount discharged through orifices in system. Do not include length of lateral 1 foot head loss is allowed in worksheet for lateral.

29 Header Effluent Delivery Pipe

30 FRICTION LOSS p. 14 of 24, PD Worksheet, SPM Appendices. How much friction loss in 1 ¼ pipe, 65 long with 4-90 elbows, where 25 gallons/minute is discharged from all orifices? See step 6 in pressure distribution worksheets for minimum flow rates in pipe sizes for delivery pipe need to maintain velocities. How do you know what size to choose? Somewhere in 5 to 10 head loss for the volume needed.

31 FRICTION LOSS P. 16 of 24, PD Worksheet, SPM Appendices.

32 CHOOSING & EVALUATING DOSE VOLUMES Number of doses per day. How many should you have? How large should each dose be? Volume needs to fill piping and deliver dose. How much needs to be pumped to fill piping and deliver dose. How much has to be pumped to put the desired dose on the soil? Consider the 5X lateral pipe volume rule of thumb to put the desired dose on the soil when designing the system.

33 EXAMPLE A mound is 100 long, and 4.5 feet wide, with 6 laterals. It is centre fed. Designer chose 1 ½ pipe for the laterals. Peak flow design is 450 gallons for the 4-bedroom home. 4 people live in the home, at an average of 50 gallons/person. Total average flow is 200 gallons. Dosing should be 1/5 of average flow so that it equals 40 gallons per dose. Can each dose be 5X the volume of the piping? If not, what design change can be made?

34 WHAT ARE THE PROBLEMS ENCOUNTERED OR CREATED IN THE DESIGN OF A PRESSURE DISTRIBUTION SYSTEM? Could more harm than good be done if designed incorrectly?

35 WHAT HAS TO BE CHECKED ONCE THE SYSTEM IS IN? Is a squirt test really needed? Why? What do you need to observe in the test? Should you record the squirt height? Why? What benefits do clean-outs provide at end of lateral?

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37 CHOICES & DECISIONS YOU MAKE Choose squirt height Choose orifice size Choose orifice spacing Consider splitting laterals into separate zones Choose header location (end vs. centre) Determine lateral length Determine lateral diameter Choose delivery pipe size Determine pressure head loss in delivery pipe based on GPM through all orifices

38 INSTALLERS CHOOSE A SYSTEM & MAKE THE CHOICES DURING SYSTEM DESIGN Start with determining information needed and drawing out your lateral layout. Use appropriate tables and Pressure Distribution Worksheet to design pressure system.

39 EXAMPLE 1 A mound is 165 long, and 4.5 feet wide. It is centre fed. Choose 1 1/4 pipe for the laterals. Peak flow design is 550 gallons for the 6-bedroom home. 6 people live in the home, at an average of 50 gallons/person. Total average flow is 300 gallons. EXAMPLE 2 A mound is 90 long, and 5 feet wide. It is centre fed. Choose 1 1/2 pipe for the laterals. Peak flow design is 300 gallons for the 3-bedroom home. 5 people live in the home, at an average of 50 gallons/person. Total average flow is 250 gallons.

40 EXAMPLE 3 A mound is 180 long, and 4 feet wide. It is centre fed. Choose 3/4 pipe for the laterals. Peak flow design is 450 gallons for the 5-bedroom home. 7 people live in the home, at an average of 350 gallons/person. Total average flow is 350 gallons.

41 QUICK REVIEW Get even distribution Demand vs. timed dosing Lay out the distribution system Make choices regarding: piping, orifices, and volumes Use worksheets for calculations