(TTV) FLUSH SYSTEM FOR DAIRY FACILITIES

J.P. Harner, J.P. Murphy and J.F. Smith

summary

Flushing characteristics of a tower tank valve flushing system with 12 in diameter manual valve were determined. Data were obtained using the outside cow alleys in a four row freestall barn. The alleys were 12 ft wide and 420 ft long with a 2 percent slope. The average flow rate exceeded 8,000 gpm when the average head was above 30 ft and the manual valve opened 80 degrees. Opening the valve to 90 degrees increased the flow rate to over 9,700 gpm. The velocity of the flushing wave was 8.5 fpm with a flow depth of 3.5 in. The estimated wave duration or alley contact time was 14.6 sec with a 25-40 sec release time from the flush tank. The flow rate ranged from 5,300 gpm to 7,200 gpm when the average head was between 16 and 28 ft.

(Key Words: Flushing, Manure, Water, Freestall.)

Introduction

Flushing systems which collect and transport manure are utilized in dairy operations.

It offers the advantage of labor reduction with automated systems, limited scraping requirements, lower operating cost, drier floors, potential reduction in odor and cleaner facilities. An optional method of handling the manure may be necessary during colder weather which is a disadvantage. Other disadvantages include the water requirements per cow and the initial fixed cost.

Designed flush systems utilize a flush device to release the correct volume of water at the appropriate discharge rate and length of time. This achieves the designed flow velocity, contact time, and depth of water in the gutter to obtain adequate cleaning.

Daily water requirements for flushing vary depending on the width, length and slope of the flushed area. Buildings with alleys sloping 2 to 4 percent will use less water for flushing when compared to alleys with a 1 percent slope. At an optimal slope of 3 percent, a minimum flush volume is 100 gal per ft of gutter width for flushing lengths of less than 150 ft. Longer lengths require more water with a suggested maximum release of 175 gal per ft. One study found 40 to 50 gal per cow per flush were required for effective flushing. A study of six dairies found flush water requirements ranging from 240 to 620 gal per cow per day. Another design procedure suggests selecting the larger of two volumes - either 52 gal per cow per flush or 1.35 gal per sq ft of alley per flush.

Most flushing systems utilize purchased components which include pipe line systems using pop-up valves or plates and underground piping. The objective of this study was to develop a tower tank valve (TTV) flushing system which could be incorporated into an existing or new dairy using sand bedded freestalls. Desired flushing characteristics included a release rate of 9,000 to 10,000 gpm, water usage of 4,200 gal per flush, 30 sec flushing interval and the ability to move sand laden manure. Procedures A TTV system was installed at a dairy in North Central Kansas. The freestall building was 420 ft long with a 2 % slope. The alleys had a one in slope towards the freestall curb from the outside wall. The four row barn had 84 freestalls per row. The feed alley was 14 ft wide and the cow alley was 12 ft wide.

The TTV flush system consisted of open-top flush tanks which are 10.4 ft. in diameter and 38.5 ft. tall. The flushing system uses a 6 to 7 ft section of 16 in pipe exiting the tank at a right angle. The 16 in pipe has a 45 degree slope inside the tank. Another 6 to 7 ft section of 12 in pipe, which includes a 12 in manual gate value, is then used to carry the water to the flush alleys. The pipe outlet directs the water along the freestall curb.

Data and measurements were taken using the upper 200 ft of the 12 ft alleys while the cows were milking. Except for the first flush, the alleys were free of manure and sand. During the study, the gate value was opened 80 degrees for the first study and then 90 degrees during the sec.

Tests were conducted at the site on two separate days. Measurements taken during the study used the 12 ft outside alleys and the data averaged together based on initial head. The flush water velocity was measured at a distance of 50 ft and 100 ft from a reference point. The reference point was located 90 ft from the outlet of the flush tank. The water front reached uniform flow prior to the reference point. Stop watches were started as the wave front passed the reference point and then stopped as it traveled past the known distance. The flush velocity was determined by averaging the velocities of the wave traveling 50 and 100 ft.

The flush tanks were equipped with pressure gages to measure the water pressure before and after each flush. The difference in pressure was used to determine the drop in water elevation and the water volume released. The average discharge rate was determined by the water volume release during a given time. The time interval was based on the time the valve was opened. The actual flush was normally 2 to 3 sec longer which was the time interval required to fully open the valve. The flush value was closed after the front had traveled 200 ft. or approximately 30 sec. The steady state release volume was not measured. However, based on Bernoulli equation and using the friction losses of the different components, the estimate steady state rate was 10,500 gpm.

The flow depth was determined at the reference point and the 50 and 100 ft intervals. The depth was determined by measuring the distance from the top of the curb to the top of the flush water and then subtracting this value from the total curb height. After the flush tanks were filled, the fill value was closed. Multiple tests were conducted until the tank depth was below 10 ft.

Results and Discussions

Table 1 present the results of the data collected when the valve was 80 degrees open. The discharge rate was a function of initial head and varied from 8,700 gpm to 5,000 gpm. The initial head varied from 34 ft to 16 ft. The wave velocity ranged from 7 to 10 fpm with an overall average of 8.5 fpm. The average water depth was 4 in.

Table 2 presents the results of the sec. study with the valve opened 90 degrees. Discharge rates increased a minimum of 500 gpm as compared to opening the valve only 80 degrees with a similar initial head. There was a reduction in velocity from 11.5 fps to 6.7 fps as the head reduced from over 30 ft to less than 10 ft. The depth of wave also reduced about 50 percent as the initial head reduced.

The water usage based on a 8,500 gpm discharge rate and a 30 sec flush is equal to 0.84 gal per square ft, a flow rate of 700 gpm per ft width of gutter and a water usage of 350 gal per ft of gutter. Based on number of freestalls and flushing three times per day, the water usage was 48 gal per stall per flush or 140 gal per day per stall. Based on a 30 sec flush three times per day in the milk parlor, the water usage in the milk parlor was 39 gal per stall per day. The flush system removed the sand and manure from the alleys based on visual inspections.

Summary

Procedures were developed for determining on-site the performance flushing systems. The flushing parameters of tower tank valve flush system exceeded current design recommendations. The modifications simplified the construction process and ease of maintenance. If repairs are necessary, the whole system does not have to be drained unless the pump has to be replaced. The manual values can be replaced by electric driven actuators with flush intervals based on time. The TTV flush system is also able to adapt to existing dairies providing there is room to handle the flush water at the lower end. One disadvantage to a TTV flush systems is more tanks are required. The initial cost appears to be similar to pipe line systems which use underground piping to equalize the pressure between two tanks.

It is important that the flush tank release rate be considered at the upper and lower end of the alleys. Sand traps and gravity solid settling basins need to be designed to handle higher velocities of flush water. Based on visual inspection of the alleys, it is suggested with sand bedded freestalls the minimum flush velocity be 7.5 fps with 10 fps being preferred. Current recommendations on release rates appear to be adequate based on this study and with 400 ft alleys. The water depth at the freestall curb should be a minimum of 3 in with 4 in preferred. The energy of the flush water needs to be directed along the freestall curb rather than in the center of the alley with sand bedded freestalls. This enables the flushing system to remove sand away from the curbs and avoids having to occasionally scrape the sand away from the curbs. Properly designed flush systems can be utilized for effective removal of sand laden manure in new or existing dairy facilities.

Table: 1 Characteristics of flushing system with valve 80 degrees open

Initial Head (ft)	No. of Rep	Velocity (fps)	Flow Rate1 (gpm)	Flow Depth(in)	Contact Time2 (sec)
? 30	2	10.6	8,420	4.9	11.5
26 - 30	2	9.8	8,150	3.9	13.9
21-25	3	8.5	6,360	4.2	12.2
16-20	3	7.8	5,670	3.7	13.0
11-15	No measurements taken
6-10	No measurements taken

1 Average flow rate based on from opening to closing of valve.

2 Estimated based on released rate, flow depth, velocity.

Table: 2 Characteristics of flushing system with valve 90 degrees open

Initial Head (ft)	No. of Rep	Velocity (fps)	Flow Rate 1 (gpm)	Flow Depth(in)	Contact Time 2 (sec)
? 30	3	11.5	9,740	3.6	11.2
26 - 30	3	10.8	8,630	3.6	11.9
21-25	2	9.4	7,760	3.0	13.4
16-20	3	8.3	7,390	3.3	15.4
11-15	3	7.6	5,940	3.0	16.3
6-10	3	6.7	5,010	2.5	20.0

1 Average flow rate based on from opening to closing of valve.
2 Estimated based on released rate, flow depth, velocity.

Source: Kansas State University
Author: Murphy Smith