1 Pressure Distribution Design 2 Let s Start with Nonpressurized systems Historically the norm 3 Distribution Systems 4 Distribution Systems Non-pressurized Distribution Non-pressurized Distribution (cont.) 5 Progressive Failure 6 Why use Pressure Distribution 1
7 The Benefits 8 Distribution Systems Creates Unsaturated Flow Minimizes movement through pore spaces Slows the flow through the soil Better distribution of effluent Lower hydraulic loading rate Lower organic loading rate Resting periods improves oxygenation Air is pulled in behind the effluent Allows flow monitoring Basically better treatment and longer system life Pressure Dosed mounds and beds 9 Distribution Systems 10 Distribution Systems Pressure Dosed - trenches Pressure Dosed sand filters 11 Example Configurations 12 Non-Level Pressure Distribution End Feed System Center Feed System Mulit-zone Feed System 2
13 Design Options for Balancing 14 Valves to Balance Head Adjust distribution network design Perforation size, spacing Pipe diameter Split system into zones which are at the same elevation Distributing valves (pressure actuated or solenoid) Duplex pump system Use valves to balance head pressure Need to pressurize lines (fill with water) Adjust valves so squirt heights are even 15 Flow regulating valves Adding one increases friction Should NOT be a ball valve Gate valve is better Globe valve is best but most expensive 16 System Design 17 Rules of Thumb 18 Rules of Thumb (cont) Transport Line Size (from pump to PDS) Consider Head Losses smaller pipe = higher head loss (larger pump) Consider Drainback Larger pipe = more drainback Consider Cost Larger pipe costs more 1.5 to 2 is typical Manifold Line Size Typically match the transport line or larger Lateral Line Size Maintain less than 10% flow differential from 1 st to last orifice Laterals are typically smaller than Manifolds (each lateral transports a smaller flow rate than the manifold) 1 to 1.5 is typical Orifice Spacing Try to maintain a grid (i.e. 2 by 2 or 3 by 3 etc.) More orifices provides better distribution More orifices causes high flow rates 3
19 Rules of Thumb (cont) 20 Rules of Thumb (cont) Residual Head at Last Orifice (squirt height) 1/8 orifice = minimum 3 5 squirt 3/16 orifice = minimum 3 5 squirt 1/4 orifice = minimum 2 squirt Orifice Size 1/4 orifice Often not used due to high flow rates from each orifice 3/16 orifice Requires larger pumps Larger dose volume may not maintain unsaturated flow Can be used with most applications Minimum size recommended with low-head pumps 1/8 orifice Can be used with screened or pretreated effluent, and highhead pumps 21 Squirt Height vs. Flow per Orifice 22 Pump Curve Comparison 23 Rules of Thumb (cont) 24 Rules of Thumb (cont) Dose Volume Distribution is poor during filling and draining the network (before and after pressurized) Especially important with larger orifices Dose at least 4 times the volume of the distribution network; plus 1 times the volume of the transport pipe Minimize the diameter of long transport lines that drain back When to Use an Automatic Distributing Valve For large systems, a valve keeps zones small, which allows smaller, more reasonably-sized pumps. For multiple zones at different elevations. For multiple zones in different areas. To alternately dose different zones. 4
25 Hydraulic Switching Valves 26 Hydraulic Switching Valves Pressure actuated (no power needed) Have clear PVC pipes where flow can be verified Have ball valve for testing the zone cycling Can be removed, disassembled, and cleaned Need occasional servicing DO NOT Install Upside Down! 27 Sequencing Valve Concerns 28 Other Recommendations for Pressure Distribution Systems Should be used with screened effluent High head pumps tend to make them more reliable More reliable with pre-treated effluent Must have access Maintenance - taking them apart, cleaning the internal components and reassembling Must have periodic servicing Must have freeze protection Liquid in the legs of the valve Screen septic tank effluent Use higher-head pumps to scour pipes and clear orifices Use orifice shields to prevent gravel from masking the orifices Face orifices downward in cold climates Use flushing valves to clear debris 29 Flushing Valves 30 Lateral Cleanouts 5
31 Valve boxes 32 Choosing a Pump Size a Pump to meet the Goal Obtain a design Gallon per Minute (GPM) and a Total Dynamic Head (TDH), which is needed to choose a pump. 33 Total Dynamic Head 34 Design References US EPA Onsite Wastewater Treatment System Manuals, 1980 and 2002. Otis, R.J. 1981. Design of Pressure Distribution Networks for Septic Tank Soil Absorption Systems. Small Scale Waste Management Project. Converse, James C. 2000. Pressure Distribution Network Design. Basically extracted and modified version of the Otis paper. WA State Dept. of Health. July 2009. Pressure Distribution Systems. This is a design guidance document. Several Health Departments have similar documents. Utah On-Site Wastewater Treatment Training Program 35 Design Tables and Charts 36 Design Software Streamline - by Miller Environmental Corp PumpSelect - by Orenco Systems, Inc. 6
37 Squirt Test 38 Management of Pressure Distribution 39 Determining Distal Head 40 Impacts on Management Attach the clear stand pipe to lateral end [Pressure gauge] Turn on pump Measure and record pressure head in feet Compare this to initial design and code requirements Smaller holes = Higher Frequency ¼ ~ 3 years 1/8 ¼ ~ 2 years 1/16 ~ 1 year Switching valves ~ 1 year Pressure Control Valves ~ 1 year 41 Questions? 7