Presentation on theme: "DRIP DISPERSAL SYSTEMS Problems and Solutions Presented by Keith Surface."— Presentation transcript:
DRIP DISPERSAL SYSTEMS Problems and Solutions Presented by Keith Surface
Flow Equalization Surges in the ATU during peak loading events are a major contributor to filter clogging in a drip dispersal system. One good solution to this problem is utilization of a flow-equalization system. WARNING: If a flow-equalization system or lift station is not set up properly, it can greatly disrupt the operation of the ATU. IT CAN DO MORE HARM THAN GOOD!
Flow Equalization Rate-of-Flow NSF Standard 40 Testing – 5 gallons of residential strength wastewater are introduced into 500GPD ATU through a dump station and piping mechanism 100 times a day. Morning: 35 dumps - 1 dump approx. every 5.1 minutes for 3 hrs (average = 0.98gpm) Afternoon: 25 dumps - 1 dump approx. every 7.2 minutes for 3 hrs(average = 0.69gpm) Evening: 40 dumps - 1 dump approx. every 4.5 minutes for 3 hrs (average = 1.1gpm) Recommended dosing flow for a 500GPD ATU is 1- 5 GPM. Effluent Pump Flow Rates 1/3hp effluent pump - 44-55gpm @ 5ft/head 1/2hp effluent pump - 90-120gpm @ 5ft/head Lift Station: A lift Station that has 12inches between the on and off switch can discharge 200gallons in 4 minutes. (Based on 16.5 gallons per inch)
Rate-of-Flow Rate-of-flow is the most important consideration when utilizing flow equalization. Major Concern: Is a mechanism in place to adjust and measure rate-of- flow? Mechanisms to adjust and monitor rate-of-flow. 1. Ball valve followed by union in pump tank. 2. Ball valve followed by union in ATU riser 3. Water-meter with gate valve in valve box. (standard meter tends to clog) FACT: If installer or maintenance provider cannot demonstrate how they measure the rate-of-flow, they do not know what the actual rate-of-flow is!
Flow-equalization for multiple ATU’s Adjustment and measurement
Flushing the Drip Tubing Will the Drip System Function As Designed 2 Years From Now? If a mechanism to adequately flush the drip tubing is not built into the drip dispersal system, we cannot protect the ability of the dispersal system to function long term. The wastewater drip tubing manufacturers do not warranty their products against clogging of the tubing or emitters. Flushing Methods Intermittent Flush - Drip tubing is flushed intermittently back to pretreatment tank. Continuous Flush - Drip tubing is flushed continuously back to pump tank during field dosing cycle.
Intermittent Flush Drip tubing is flushed intermittently back to pretreatment tank. Pros: Full velocity flush - Allows metering of flow – Less demand on filter than continuous flush – Does not stir pump tank effluent Intermittent Flush Methods 1. Automated Controls and solenoid valve. Pros: Automation and precise control. – Electronic Monitoring Cons: Initial Cost – Trouble shooting – Repair 2. Non-electric flow-activated field flush controller Pros: Automated - Lower initial cost - Flushes beginning of each dosing cycle Cons: Increases time from pump start up to full field pressurization. 3. Manually operated valve. Pros: Inexpensive Cons: Relies on technician to insure that tubing is adequately flushed. Flushing is only done during scheduled maintenance visits.
Continuous Flush Drip tubing is flushed continuously back to pump tank during field dosing cycle. Pros: Low initial cost Drip tubing is continuously and automatically flushed. Does not depend on technician or controllers to insure that tubing is properly flushed. Cons: Effluent is continuously filtered (3 to 4 times more that intermittent flush) which makes filter clogging more likely to occur. Pump tank is continuously stirred which makes filter clogging more likely to occur on systems that do not use self-cleaning filter. Cannot meter flow accurately Note: Under most conditions, setting the continuous flush valve to retain 10psi will cause a 10% to 20% flow reduction as compared to open flow.
Field Pressurization with Continuous Flush For pressure compensating emitters, pressure at the emitter needs to be between 10psi – 50psi. 1. Ball valve Pros: Inexpensive Cons: Increases field pressurization time Field pressure changes as filter clogs. Field pressure is usually guess-work Increases time from pump start up to full field pressurization. 2. Self-adjusting valve Pros: Does not increase field pressurization time. Valve closes when pressure drops below 10psi Keeps field pressure constant Adjust to pressure loss due to partially clogged filter
Scouring Velocity What is required to adequately flush the drip tubing? Netafim “suggests” 2ft/sec - Geoflow recommends 0.5ft/sec to 1ft/sec The wastewater drip tubing manufacturers do not warranty their products against clogging of the tubing or emitters. Many regulations across the country now require that 2ft/sec be utilized as design scouring velocity for wastewater drip installations. 2ft/sec = 1.6gpm 1.6gpm required through each lateral during flushing cycle. 10 laterals will require 16gpm to flush at 2ft/sec. (This does not include the flow “lost” though the emitters.)
Flushing Example 1: Flow Requirement with 12 – 100ft laterals = 1200 lineal ft 1200ft of 0.6gph drip tubing Emitter discharge = 6GPM Inlet pressure required for 100’ laterals = 15psi 12 laterals X 1.6gpm = 19.2GPM Total Flow Required 6gpm(emitters) + 19.2gpm(flushing) = 25.2gpm at 15psi tubing inlet
Flushing Example 2: Flow Requirement with 6 – 200ft laterals = 1200 lineal ft 1200ft of 0.6gph drip tubing Emitter discharge = 6GPM Inlet pressure required for 200’ laterals = 17psi 6 laterals X 1.6gpm = 9.6GPM Total Flow Required 6gpm(emitters) + 9.6gpm(flushing) = 15.6gpm at 17psi tubing inlet
Flushing Example 3: Flow Requirement with 4 – 300ft laterals = 1200 lineal ft 1200ft of 0.6gph drip tubing Emitter discharge = 6GPM Inlet pressure required for 300’ = 25psi 4 laterals X 1.6gpm = 6.4GPM Total Flow Required 6gpm(emitters) + 6.4gpm(flushing) = 12.4gpm at 25psi tubing inlet
PUMP SIZING Required Flow 25.2gpm at 15psi Pressure loss through filter at 25.2gpm = 19psi Pressure loss through 100’ of 1-1/4” pipe at 25.2gpm = 3.5psi Pressure loss through fittings (estimate) at 25.2gpm = 1.5psi Pressure loss at 7.5’ elevation from pump to field = 3.2psi Total Pressure loss = 27.2psi Required Inlet Pressure 15psi + 27.2psi = 42.2psi Pump must produce 25.2gpm at 42.2psi Required Flow 15.6gpm at 17psi Pressure loss through filter at 15.6gpm = 7.5psi Pressure loss through 100’ of 1” pipe at 15.6gpm = 5.4psi Pressure loss through fittings (estimate) at 15.6gpm = 1.5psi Pressure loss at 7.5’ elevation from pump to field = 3.2psi Total Pressure loss = 17.6psi Required Inlet Pressure 17psi + 17.6psi = 34.6psi Pump must produce 15.6gpm at 34.6psi Required Flow 12.4gpm at 25psi Pressure loss through filter at 12.4gpm = 5psi Pressure loss through 100’ of 1” pipe at 12.4gpm = 3.6psi Pressure loss through fittings (estimate) at 12.4gpm = 1.5psi Pressure loss at 7.5’ elevation from pump to field = 3.2psi Total Pressure loss = 13.3psi Required Inlet Pressure 25psi + 13.3psi = 38.3psi Pump must produce 12.4gpm at 38.3psi Friction loss factors: Rate of flow through piping(size and length), fittings, filters, zone valves, control valves, and changes in elevation
Pump Heat Overheating is a major cause of pump failure. Pump needs a minimum 5GPM flow to insure that it will not overheat. Submersible pumps are designed for use in a well casing that forces water movement around pump motor. Extremely low flow can cause pump to overheat. Example 1: 600ft of 0.6GPH Drip Tube using intermittent flushing. Flow through emitters = 3GPM The pump for this system will likely overheat! Solutions: A. Install by-pass in pump tank on supply or return. B. Utilize continuous flushing. C. Install pump in a sleeve.
Pump Heat …continued Cavitations A continuous flush that discharges in the direction of the pump intake likely will cause pump to overheat due to cavitations through the formation of air bubbles. An “off” float switch that is set too low will cause pump to overheat due to air being drawn into pump intake. A timer override float switch can cause pump failure if the effluent filter has clogged.
System Drain Down What Happens When the Pump Turns Off? 1. Emitters become “Open Holes”! A. Laterals generally should not drain back to the pump tank. 2. Effluent flows to low point of emitter laterals. A. Laterals should be installed as level as possible. (Slope as low as 1% can cause problems.) B. Steps should be taken to isolate individual laterals from each other. 1. Elevate or lower manifolds in relation to laterals. 2. Elevate loops on laterals that are looped. 3. Effluent flows to low point of manifolds. A.Install manifolds level when possible. B. Install manifolds lower that laterals C. Install manifolds so that they drain back to pump tank. D. Do not oversize manifolds. E. Use top or bottom feed manifolds when necessary.
Micro-Dosing System Drain Down is repeated at the end of every dosing and/or flushing cycle. Example: System is dosed for 40 minutes a day (10 minutes every 6 hours), but is experiencing 2 gallons per dose drain down to lowest lateral. To compensate, dosing is set at 4 minutes for 10 doses. Instead of having 8 gallons of drain down each day (4 doses X 2 gallons drain down), system now has 20 gallons of drain down each day (10 doses X 2 gallons of drain down). DO NOT MICRO-DOSE! Dosing should be between 6 – 12 minutes. Length of Laterals: At the beginning of each dosing cycle, how long does it take the effluent to reach the end of a 400’ lateral at a velocity of 4ft/sec?
Native soil is always the best choice for tubing installation if other factors do not prohibit!