The present invention refers to pipe fittings for pneumatic transport pipes, and in particular to an elbow for connecting two pipes at an angle of 90.degree., with the elbow including a first pipe socket connected to a pipe section with expanding cross-sectional area which is followed by a second pipe socket.
An elbow of this type is known and includes a quadrantal pipe bend with a bag-like cross-sectional expansion at the outer elbow side. The provision of such a bag-like expansion results in a deceleration of the velocity of the entering flow of bulk material. As part of the bulk material collects in the space as defined by the cross-sectional expansion, a direct impacting of bulk material particles, which enter the elbow, upon the outer elbow wall surface is prevented. Even though this outer wall section is subjected to reduced wear, and thus such an elbow has a considerably increased life, the bag-like cross-sectional expansion causes an undesired pressure drop. Further, since bulk material accumulates in the formed pocket of the cross-sectional expansion, a removal of accumulating bulk material is difficult even when blow cleaning over an extended period. Thus, a complete cleaning, as required during a product change, necessitates a dismantling of the elbow.
It is also known to provide a 90.degree. elbow in form of a pipe bend which includes at the outer elbow side a cross-sectional expansion in form of a substantially spherical chamber. At operation, this chamber is filled with bulk material particles to create a vortex or ball which rotates counterclockwise to the direction of deflection so as to impart the entering flow with the desired deflection without having bulk material particles impact the outer elbow wall surface. This design desires to lessen not only wear of the pipe bend but also the change in the particle structure as well as also formation of product abrasion and formation of so-called angel hair. However, practice has shown that the parting edge, by which the bulk material flow entering the elbow is split in a partial flow which is deflected and a partial flow which enters the chamber and rotates there, as well as the rotational motion of the bulk material particles in the spherical chamber promote the formation especially of superfine abrasion. Moreover, with certain types of bulk material, the aspired suspension of bulk material particles within the flow medium cannot be attained in the spherical chamber which thus becomes increasingly filled with stationary bulk material. Therefore, an elbow of this type displays the same drawbacks as those pipe fittings previously set forth, especially with regard to a cleaning prior to a product change.
Conventional 90.degree. elbows are certainly also known which have the advantage of a low pressure drop and which are self cleaning. Still, the use of such conventional 90.degree. elbows is disadvantageous as the outer elbow side is rapidly worn off and formation of angel hair is promoted which especially is encountered during dragging of granulated particles of polyolefine along the pipe wall, in particular when operating at high conveying speeds. These drawback could be eliminated by using T-pieces with a dummy third connection which is filled with bulk material up to the area of deflection between the first and second pipe connections, with the bulk material forming an interface in form of a baffle plate for the entering flow of bulk material; however, the use of such T-pieces is disadvantageous as they are not self-cleaning and result in a high pressure drop.