Transcript Drip Systems - Eng.hctx.net

DRIP DISPERSAL SYSTEMS
Problems and Solutions
Flow Equalization
Surges in the ATU during peak loading are a major cause of filter clogging in a drip dispersal
system. One 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 WILL DO MORE HARM THAN GOOD!
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 every 5.1 minutes for 3 hrs
(average = 0.98gpm)
Afternoon: 25 dumps - 1 dump every 7.2 minutes for 3 hrs
(average = 0.69gpm)
Evening: 40 dumps - 1 dump every 4.5 minutes for 3 hrs
(average = 1.1gpm)
500GPD ATU should be dosed at 1-4 GPM.
Effluent Pump Flow Rates
1/3hp effluent pump - 44-55gpm @ 5ft/head
1/2hp effluent pump - 90-120gpm @ 5ft/head
List Station: A lift Station that has 12inches between the on and off switch can discharge
200gallons in 1 to 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 monitor 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. (meter screen 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 Methods
1. Rate of Flow X Duration of Dose X # of Doses
2. Rate of Flow (1-2 GPM)
3. Homeowner education
Flushing the Drip Tubing
Will the Drip System Work 5 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. Neither Netafim nor
GeoFlow warranty their products against tubing or emitter clogging.
Flushing Methods
Continuous Flush - Drip tubing is flushed continuously back to pump tank during field dosing
cycle. For pressure compensating emitters, pressure at the emitter needs to be between 7psi –
60psi. Ball-valve or automatic flush controller such as the “SmartFlush” valve is utilized to ensure
that proper operating pressure is maintained.
Pros: Drip tubing is continuously and automatically flushed.
Does not depend on maintenance provider to insure that tubing is properly
flushed.
Cons: Effluent is continuously filtered which makes filter clogging more likely to occur
on systems that do not use self-cleaning filter.
Intermittent Flush - Drip tubing is flushed intermittently back to pretreatment tank. This is
accomplished by maintenance technician opening a valve during maintenance visits or though
automated means.
Pros: Less demand on filter than continuous flush. Field flush is not restricted as it is
when utilizing continuous flush.
Cons: If automatic flush controllers are not utilized, this method relies on technician to
adequately flush system during service visits.
Scouring Velocity
What is required to adequately flush the drip tubing?
Netafim recommends 2ft/sec - Geoflow recommends 1ft/sec
Many states are now requiring that 2ft/sec be utilized as design scouring velocity for all drip
installations that utilize intermittent flushing.
Note: A system designed at 2ft/sec that utilizes continuous flush with backpressure set at 10psi will have an approximate 1ft/sec scouring velocity.
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 0.6ghp 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 0.6ghp 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 0.6ghp 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.
Solutions:
A. Install by-pass in pump tank on supply or return.
B. Utilize continuous flushing.
Example 1:
600ft of 0.6GPH Drip Tube using intermittent flushing.
Flow through emitters = 3GPM
The pump for this system will likely overheat!
Pump 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.
System Drain Down
What Happens When the Pump Turns Off?
1. Emitters become “Open Holes” In or Out!
A. Laterals 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 manifolds slightly above the 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 so that they drain back to pump tank.
(Only use this method if you can insure that laterals do
not drain back into manifolds.)
B. Do not oversize manifolds.
C. Use top or bottom feed manifolds when necessary.
4. 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 2ft/sec?
Answer: 200 seconds or over 1/3 duration of average dosing cycle
Native soil is always the best choice for tubing installation if other factors
do not prohibit!