Flushed clean

Use these ideas to help you get a clean alley every time you flush manure from sand-bedded barns.

Sand - hailed as the premier bedding choice for udder health and cow comfort - often gets criticized for creating havoc with mechanical manure-handling systems.
Unfortunately, sand also presents a challenge for producers who use a flush system.

"Sand is the number one complaint we get with flush systems," says Joe Harner, agricultural engineer at Kansas State University. The fact that it doesn't leave easily when flushing alleys is a thorn in many producers' sides. Harner and colleague John Smith, extension dairy specialist at Kansas State University, share solutions for three of the most common problems associated with flushing sand-laden manure. Use their advice to help you avoid these problems and get a clean alley every time when flushing manure from sand-bedded barns.

Problem 1: My flush system leaves sand along the curb.

Cause: Shortly after moving into a new free-stall barn, Kirby and Dennis Hissong of Greencastle, Pa., noticed the flush water failed to wash sand away from the stall curb. This caused sand to accumulate along the curb, forcing them to push the sand away from the curb with a compact tractor and blade twice per week, says Dennis Hissong, a partner in the 500-cow dairy.

The Hissongs aren't alone in experiencing this problem. Sand along the curb is one of the top three problems producers experience when flushing sand-laden manure.

Sand gathers along the curb for one or more of the following reasons: insufficient flush water volume, inadequate flushing frequency or improper floor slope, says Harner.

Solution: In existing facilities, you can alleviate the problem like the Hissongs do - by manually scraping the sand toward the center of the alley with a tractor blade or skid steer. That, however, creates "another chore we have to do," says Dennis Hissong.

Another way to minimize sand along the curb is to increase the number of times you flush your free-stall alleys during the day. Flush alleys every two or three hours, suggests Harner. Use caution when doing this as recycled flush water that splashes onto cows' udders can decrease milk quality.

Grooming the stalls at every milking can help reduce the amount of sand kicked into the alley, adds Smith. This, in turn, reduces the amount of sand that the flush system must remove from the alley.

But perhaps the best way to stop sand from settling along the curb is to pay attention to water volume during the initial design. At that time, aim for a release, or discharge rate of 10,000 gallons per minute. This volume of water generates enough energy in the flush wave to move sand away from the curb. The release rate depends on the length and slope of the alleys. Use the table on page 23 to determine an appropriate release rate for your facility.

During the initial design, it's also a good idea to slope the concrete floor toward the curb instead of the center alley, adds Harner. This directs the energy of the flush water toward the curb and aids in removing sand from this area. Aim for a 0.5- to 1-inch slope from side to side.

Problem 2: Sand settles at a bend or 90-degree turn.

Cause: Whenever sand-laden flush water is forced to "bend" or turn 90 degrees into an alley or gutter, the flush wave loses velocity, causing sand to settle at the turn.

Think of it this way: As water flows around a bend in a creek or stream, it slows down and deposits sand along the outside of the bend. "Anytime we change velocity, we're going to settle sand," explains Harner.

Solution: Using a gentle curve, as opposed to a sharp 90-degree turn, "would help quite a bit," says Harner. However, facility design often impedes this option. For example, this wouldn't be possible to do with flush water from a holding pen that must turn 90 degrees into a center alley that is designed to collect flush water and direct it to the manure-handling area. Sand settling also can occur when you use cow travel lanes to transfer flush water back to the lagoon.

You can, however, help sand make a 90-degree turn by increasing your flush-water release rate. This increases the flush water's velocity and minimizes the amount of sand that settles out.

To find out if an inadequate release rate is your problem, first determine how much water your system is currently releasing. To do so, you will need to know the following: 1) the length of time the flush valve stays open during a flush session and 2) the amount of water actually used during a flush.

If you operate a pump flush system - one that uses a pump to move water from the lagoon to the release valve - the pump manufacturer should be able to tell you the amount of water you use during a flush.

In a tower or tank flush system - a system that stores flush water in a tank or tower - determine the amount of water used during a flush by noting the volume of water in the tank before and after you open the flush valve, says Harner.

Next, use the following equation to determine your flush system's re-lease rate:

Volume of water used
÷ length of time flush valve stays open
= release rate

For example, let's say your system uses 5,000 gallons of water, and the flush valve stays open 30 seconds or 0.5 minutes.

5,000 gallons of water used
÷ 0.5 minutes
= 10,000 gallons per minute release rate

Use the table on page 23 to find out if the release rate you calculated is sufficient to clean the alleys in your barn. Remember, the release rate needed in your barn depends on the length and slope of the alleys.
Problem 3: Sand settles at the lower end of the alley or before it reaches the separation system.

Cause: Flush water collects at the lower end of an alley before it exits the barn. From there, a transfer system - troughs, lanes or pipes - moves it to a mechanical or gravity manure-separation system. However, when the transfer system can't handle the volume of water that is released during a flush cycle, sand settles before it reaches the separation system. Sometimes, flush water backs up into the alley. The problem is due to mismatched flush-system components. That is, the components at the "back end" of the flush system - the transfer troughs, lanes or pipes that carry the water to a separation system - can't keep up with the volume of water released from the "front end" of the flush system.

Solution: "If the total system is not designed to handle the water release rate - 500 or 5,000 gallons per minute, for example - then additional energy will be needed to move the sand to the separator or away from the alleys," says Harner. That means you'll probably need to move the sand to the separation area with a skid-steer or augers.

During the initial design of a barn, make a conscious effort to maintain a constant velocity from all the way through the system. Look for areas in the initial blueprint that could slow the flush velocity and cause sand to settle. Take steps to correct the problem before your facility is up and running.

Don't forget about slope

Barn slope is vital to the success of a flush system.

"Slope is very important," says Don Bennink, who operates North Florida Holsteins in Bell, Fla. Bennink's advice to producers who are thinking about installing a flush system in a new barn: Make sure the building has enough slope.

"If you're going to flush sand, you're going to have to have more slope or you'll have to supplement with some scraping to keep (the sand) from building up," he says.

When designing a new facility, slope the alleys 1.5 percent to 2 percent, recommends Joe Harner, extension agricultural engineer at Kansas State University. Proper slope can prevent bottlenecks down the road.



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