Of the various methods Openchannelflow has developed for conditioning flow for flumes, Tranquilizing Racks are the most common.  Tranquilizing Racks are vertical "fingers" that extend down into the flow to break up poor velocity profiles and develop uniform, straight line flow parallel to the longitudinal axis of the flume.  Tranquilizing Racks are most commonly used when there is an insufficient straight run of pipe upstream of the flume (usually 15-25 pipe diameters are required, depending upon the type of flume) or where there are abrupt channel bends upstream of the flume. 

Openchannelflow Tranquilizing racks are available for all flume styles and sizes, although they are most often used in Parshall and Palmer- Bowlus flumes.

How Tranquilizing Racks Work

Tranquilizing racks are most commonly used used in sets of two or more - with the first set breaking up the approaching flow and the second (or third) set to straighten the flow before it enters the point of measurement.  Depending upon the size of the flume, the racks can be either bolts to the top flanges of the flume or they can slide down into recesses molded in the sidewalks of the flume - allowing them to fitted only when needed. 

Used With Energy Absorbers

For applications where particularly energetic piped flows, Tranquilizer Racks are used in conjunction with Energy Absorbers.  In these applications the Energy Absorber breaks up the piped flow and then the Tranquilizer Racks (usually a set of two) straighten out the flow as it enters the flume. 

Alternatives to Tranquilizing Racks

In more mild flow conditioning applications - or where the flume is small - Perforated Plates can be used in lieu of Tranquilizing Racks.

In other applications, Tranquilizing Racks can be omitted by having the flow rise up into the flume, either through a change in piping or a Riser Box assembly upstream of the flume.  H-flume approach sections lend themselves well to the rise up method, as do do Openchannelflow's custom weir boxes. 

Clean Flows Only

Tranquilizing Racks are only for use on clean flows or those flows with only fine suspended solids.  The "fingers" of a Tranquilizer Rack will act as a bar screen on flows containing sanitary or other larger solids.

Bar Screen Variation

A variation of the Tranquilizer Rack inclines the top of the Rack back towards the flume.  Here the Rack is actually designed to act as a back up bar screen should there be any breakthrough of solids upstream of the flume.  In these applications care must be taken so that the Tranquilizer Rack does not become blinded (clogged) by debris - potentially backing up flow until it overspills the upstream channel banks.