U-Shaped Distribution Tube

Overview

Flap valve filter technology originates from the Swiss company Sulzer and takes its name from the backwash drain valve plate, which swings through 0-90 degrees during operation. Flap valve filters offer a high dirt-holding capacity, good filtration performance, savings on backwash water and a high degree of media cleanliness after backwashing. The filter structure is also simple and the investment low, so the technology has been progressively adopted in China in recent years.

The distribution system of a flap valve filter is of the low-resistance type. A water and air distribution system made up of lateral distribution pipes, vertical distribution water pipes and vertical distribution air pipes forms a double-layer air and water distribution arrangement in the main distribution channel and in each of the lateral distribution pipes. Because the distribution pipes inside the filter are independent of one another, this arrangement gives the flap valve filter theoretically good distribution uniformity, and the construction tolerances required are lower than for conventional low-resistance distribution systems.

The backwashing method of a flap valve filter differs from other air-water backwash filters: it uses closed-valve backwashing, in which the washing and drainage stages are separated. No water is drained during either the water wash or the air scour; the flow is left to stand for several tens of seconds after each washing stage before draining. As a result, a correctly commissioned flap valve filter shows virtually no loss of media.

Performance

The water and air distribution system of a flap valve filter consists of the central channel of the filter, the vertical distribution water and air pipes embedded in the roof slab of the central channel, and the lateral distribution pipes laid on the filter floor and connected to the vertical distribution pipes.

The lateral distribution pipes are made of HDPE (high-density polyethylene) and have a cross-section that is round on top and square below. The upper semicircular part forms the air distribution space and the lower square part the water distribution space. Water distribution orifices are drilled in the bottom of the pipes to the open area ratio required by the design, air distribution orifices are provided on both sides, and air release holes are set at the top of the pipes.

The vertical distribution water and air pipes are made of stainless steel or plastic, and the air pipes have vent holes. The vertical water and air distribution pipes are embedded when the roof slab of the filter central channel is cast, ensuring that the top and bottom elevations of all water and air distribution pipes within a single cell are identical.

Technical Parameters

Flap Valve

Valve Construction

The flap valve consists mainly of four parts - the cylinder, the drive crank arm, the valve plate frame and the valve plate. All four are fabricated from high-strength stainless steel.

Operating Principle

Compressed air is used as the driving force: the cylinder piston rod drives the crank arm and the valve connecting rod, swinging the valve stem through 0-90 degrees to open and close.

Installation

The valve body is installed directly into a prepared opening in the tank wall, about 10-20 cm from the media surface. The drive crank arm is mounted on the wall of the drainage channel, and the cylinder on the cover plate of the drainage channel.