Valves
creating the potential for material cross- contamination. However, installing the valve vertically, so that the material fl ows upward, eliminates this problem because gravity eventually pulls any material from the segment.
A naturally occurring high- pressure airfoil, as shown in Figure 3, prevents most of the material from entering the closed-line segment, defl ecting it back into the material stream. However, the airfoil can’t completely prevent cross-contamination because a small amount of material can still fi nd its way into the segment if the valve isn’t installed vertically.
FLEXIBLE-TUBE DIVERTER VALVE
The fl exible-tube diverter valve, as shown in Figure 4, operates similarly to the sliding-blade diverter valve to divert fl ow in a conveying line. A tube stub is welded directly above a sliding blade’s hole, which is installed just like a sliding-blade diverter valve, and a fl exible hose is attached to the tube stub. The fl exible hose is then attached to the upstream conveying line. To switch the fl ow from one downstream conveying line to the other, an actuator shifts the sliding blade and fl exible hose together. The fl exible-tube diverter valve can convey powders and pellets from one source to two destinations (diverter) or from two sources to a single destination (converger) in pressure or vacuum dilute-phase and pressure dense phase conveying systems. However, the valve isn’t suited to handle severely abrasive materials because they will wear the hose. The fl exible hose is typically constructed of abrasion-resistant rubber, polymer, or fl exible steel and is often housed in an open hose support frame. Some manufacturers offer an enclosed hose support frame to prevent material from spilling onto the plant fl oor if the hose fails. The fl exible-tube diverter valve can use one of two seal arrangements. One is a wear-compensating seal, which ensures that a positive air-and-material-seal
42 March 2014 Solids and Bulk Handling Figure 4. Flexible Tube Diverter Illustration
is maintained when shifting. This seal allows the valve to shift “on the fl y” and function in both pressure and vacuum dilute-phase systems. The other is a pneumatic seal, which uses an infl atable seal to handle the high pressures in dense-phase systems. With this seal, the valve can’t shift on the fl y because the seal must be defl ated before shifting and reinfl ated after shifting before the material fl ow can be restarted. One advantage of the fl exible-tube diverter valve is that very little pressure drop is created across the valve because the sliding-blade design provides smooth valve actuation and a positive air and material shutoff to the closed line. The
valve virtually eliminates material cross-
contamination because the upstream conveying line can be completely purged before the valve is shifted. However, to work
effectively, the valve’s hose must be long enough to endure the torsional stress caused by constant shifting. If the hose is too short, the constant shifting will fatigue the hose and cause it to break. Hose length depends on both the conveying line’s diameter and
MULTIPLE-SOURCE, MULTIPLE-DESTINATION DIVERTER VALVE CONFIGURATIONS
In many applications, material must be conveyed from multiple sources to multiple destinations. Traditionally, this has been done with a manually operated hose-and-manifold station, which requires a worker to uncouple an upstream line from one source and recouple it to a downstream line that carries the material to the required destination. But this manual method is less than ideal. Toxic or hazardous materials can spill when the lines are uncoupled.
Figure 5. Multi-Port Diverter Illustration
the shifting distance — the larger the line diameter or the greater the shifting distance, the longer the hose.
www.solidsandbulk.co.uk
Material can be contaminated if the upstream line is coupled with the wrong downstream line. Workers can injure themselves when uncoupling and coupling lines. Downtime for uncoupling and coupling the lines can decrease production rates. One way to successfully automate this process is to combine and stack various two-, three-, and four-way diverter valves, as shown in Figure 5. Because the operating principles of standard rotary-plug, rotary-blade, and fl apper diverter valves don’t typically allow themselves to work in these confi gurations, sliding-blade or fl exible-tube diverter valves, or a combination of them, are typically used to convey materials from multiple sources to multiple destinations. Typically, a three- or four- way diverter valve assembly is custom-manufactured for the application. The assembly tends to be compact, making it easier to install than a hose and manifold station. The assembly is independently mounted on a stand alone frame so it can be transported and installed as a single unit. The assembly can include connections for compressed air, electrical power, and operator controls. Be aware, however, that the multiport diverter valve assembly has a high onsite installation cost. ■
For more information please contact Vortex Valves on tel: 0870 770 9861 or visit:
www.vortexvalves.co.uk
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