"Reviewed December 1993" -- Extension website.Several types of flush tanks are commonly used for flushing dairies in Missouri. This publication will discuss siphon tanks and their application to flushing in a dairy operation

Fulhage, Charles Duane

Pfost, Donald L.

University of Missouri: MOspace

Focus Area Nutrients & Water Bacterial WasteQuality Published by University Extension, University of Missouri-System Siphon Tanks for Dairy Flushing Charles Fulhage and Donald Pfost, Department of Agricultural Engineering Several types of flush tanks are commonly used for flushing dairies in Missouri. This publication will discuss siphon tanks and their application to flushing in a dairy operation. Siphon characteristics Siphon tanks offer unique design and operational characteristics. Here are several advantages to using the tanks. A siphon tank can be designed and built to con­tain any volume of flush water. They are applicable to any width and/or length gutter or flush alley. Flush water rates can be tailored to each opera­ Siphon tanks can be placed adjacent to the gutter being tid-il, provided it is properly designed to deliver that flushed, so there are no traffic obstructions. rate of water. Siphon tanks can be constructed of materials that will not deteriorate in the harsh environment. In dairy operations, tank construction materials may include concrete, PVC, stainless steel or fiberglass. These materials can be expected to last as long as the facility is used. Siphon tanks are highly reliable. If properly designed and installed, the tanks operate with little or no maintenance. Because there are no moving parts to wear out, siphon tanks can provide trouble-free oper­ation over a long period of time. A siphon is used to flush this 20-foot wide dairy holding pen. A tank can be placed adjacent to the gutter to be flushed, so it does not block the upper end of the gut­ter. When the siphon tank is not actually flushing, there is no protrusion above the alley floor to interfere with traffic. Water pressure from the siphon tank raises a steel lid to allow water to flow down the flush alley. WQ316 Printed with soy ink on recycled paper Siphon tanks also have some disadvantages, rela­tive to other types of flushing devices commonly used in dairy operations. Design and construction are critical for proper operation. Siphons must be precisely designed and accurately installed. Although siphons are relatively simple hydraulic devices, it may not be immediately apparent to the builder or operator how they work. Siphons may be difficult to install in existing facilities. Tanks in dairy operations generally involve some excavation and pouring of concrete and are best installed in the construction phase of the facility. Installation of siphons may be more expensive and time-consuming than with other flush devices, such as rollover tanks. Practical construction limits the water-pressure head available in siphons, compared to water tower / pipeline-valve systems. This may impose a limit on the discharge rate and the maximum width gutter that can be flushed with a siphon. Siphons are limited to flushing a single gutter. In some cases it may be possible to flush two gutters at the same time, but design requirements usually limit such applications. In contrast, with a tower/ pipeline­valve system, several gutters can be flushed with one or two water towers. t;l0w does a siphon work? In order to understand how a siphon works, it is necessary to identify the basic components in a siphon tank (see Figure 1). BELL AIR RELEASE TANK VENT HOLE GUTrER DISCHARGE PIPE TRAP Figure 1. Components in a siphon tank. Tank. The tank is sized to discharge the required volume of water for the gutter being flushed. In dairy applications, the tank is usually concrete. Discharge pipe. The discharge pipe is sized to provide an adequate flow rate of water from the flush tank. The size of~the pipe depends primarily on the width of the gutter being flushed and the depth of water, or pressure head, in a full tank. Discharge pipes are usually PVC, stainless steel or fiberglass. Bell. The bell, similar to an inverted barrel, covers the discharge pipe so that air is trapped in the system. Usually, the bell is made of stainless steel, fiberglass or plastic. Vent hole. The vent hole in the bell allows the inside and outside air pressure to equalize after each flush. This is necessary to ensure reliable operation of the siphon. Air release. Air is released from under the bell to activate the siphon and complete a flush. Air-release devices include manually operated valves, flexible hoses or automatic trigger tubes. Trap. The trap is a reservoir under the tank that holds air in the system. The trap also provides a flow avenue for the flush water from the discharge pipe to the gutter. In dairy operations, traps are usually made of cast-in-place concrete. At the beginning of fill, after a flush, water lowers (see Figure 2). As the tank fills, water covers the vent hole in the bell and a specific volume of air is trapped under the bell and in the discharge pipe. After the vent hole is covered, the water level under the bell rises at a slower rate than the water level in the tank. The water level in the discharge pipe is pushed downward by air pressure as water rises inside the bell. See Figure 3 for the water level at the end of the fill cycle. Figure 2. Water levels in a siphon tank at the beginning of a fill cycle following a flush. Figure 3. Water levels in a siphon at the end of the fill cycle. Page 2 WQ316 or equiv. L dowel. T 74~"._6j4" 1.~L_B~E_N_D_S_T2 11 PVC STANDPIPE DRAIN/OVERFLOW, cut off 2" top of tank wall. - #4 BARS, Horiz. in top 12" of tank wall, lap 30 bar dia. around or equiv. L dowel. TANK VERT. STEEL #4 BARS, 12" o.c. outside face 1.5" cover typo HORIZ. STEEL #4 BARS, 10" o.c. lap 30 bar dia. around corners 9=6j:=IIj1••• __ bar dia. in walls or equiv. L dowel. E-=E~L-=U..:P~t~O-:--la_PJ31~'OE]#4 BARS 1211 o.c.b.w. in tank floor middle, bend continuous around 20" discharge pipe. _ HORIZ. STEEL #4 BARS, 1011 o.c. in middle,t GUTTER LIP lap 30 bar dia. around corners or equiv. L dowel. 3:1 EARTH SLOPE 3811 away 'from tank floor VERT. STEEL #4 BARS, 16" o.c. typo1 20" 11 COMPACTED EARTH 10 #4 BARS 12" o.c.b.w. OR GRAVEL FILL under tank as required After the tank fills, a flush is started by the opera­tor releasing the pressurized air under the bell through the air-release device. The air-release device remains open until air is purged from the system. As water replaces air in the system, flow begins (see Figure 4). Figure 4. Siphon conditions after the air release device is opened. Air under the bell is displaced with water and the flush flow begins. After flow is established, the water level in the tank co,ntinues to drop until air enters the system underneath the bottom edge of the bell and the siphon breaks. Since the vent hole is exposed at this point, air is admitted into the bell until pressure exists inside the bell and conditions are correct for the next fill cycle (see Figure 2). Siphon design There are several precise dimensions and installa­tion techniques necessary to insure proper siphon operation (see Figure 5): ·Tank depth •Bell area and bell height • Discharge pipe diameter •Vent hole diameter and position •Height of discharge pipe in tank •Distance pipe extends into trap under tank •Depth of trap under tank Siphons must be designed to flush the required volume of water at the proper rate. Additionally, dimensions must be correct to obtain the proper water levels and air volume in the system when the tank is full (see Figure 3). Although siphons can be designed by hand calculations, the large number of input variables is best handled by a computerized design program. Siphons should be designed by indi­viduals familiar with the operation and requirements. Figure 5. The cross-section of a siphon constructed on-site with a concrete tank. WQ316 Page 3 Siphon construction Siphons used in dairy operations generally use reinforced concrete for the tank and trap underneath. Tanks are usually 4 to 8 feet deep. Discharge pipes may be stainless steel, PVC or fiberglass. Figure S is a tank designed to flush an 8.S-feet wide alley in a dairy freestall barn and should not be used for other siphon designs. Although most siphons are constructed on-site, there are a few commercially available siphons for flushing dairies, (see Figure 6). CONCRETE TANK POURED IN PLACE ON SITE _-- GUTIER SLOPE Figure 6. A commercially available siphon tank. (Courtesy of the Farm Co., Uniontown, Kan.) IGI IThis guide was published with funds provided to the - Missouri Department of Natural Resources from the ~ ~ Environmental Protection Agency, Region VII. To learn more about water quality and other natural resources, contact the Missouri Department of Natural Resources, P. O. Box 176, Jefferson City, MO 65102. Toll free 1-800-334-6946. • Issued in furtherance of Cooperative Extension Work Acts of May 8 and June 30, 1914, in coopera­~\l University tion with the United States Department of Agriculture. Ronald J. Turner, Interim Director,~Extension Cooperative Extension, University of Missouri and Lincoln University, Columbia, Missouri 65211. UNIVERSITY OF MISSOURI • An equal opportunity institution. COLUMBIA Page 4 WQ316 New 10/93/3.5M 

Siphon Tanks for Dairy Flushing (1993)

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